Shadows of Forgotten Ancestors

Biology is much more like language and history than it is like physics and chemistry. Why we have five fingers on each hand, why the cross-section of the tail of a human sperm cell looks so much like that of a one-celled Euglena, why our brains are layered like an onion, involve strong components of historical accident. Now you might say that where the subject is simple, as in physics, we can figure out the underlying laws and apply them everywhere in the Universe; but where the subject is difficult, as in language, history, and biology, governing laws of Nature may well exist, but our intelligence may be too feeble to recognize their presence—especially if what is being studied is complex and chaotic, exquisitely sensitive to remote and inaccessible initial conditions. And so we invent formulations about “contingent reality” to disguise our ignorance. There may well be some truth to this point of view, but it is nothing like the whole truth, because history and biology remember in a way that physics does not. Humans share a culture, recall and act on what they’ve been taught. Life reproduces the adaptations of previous generations, and retains functioning DNA sequences that reach billions of years back into the past. We understand enough about biology and history to recognize a powerful stochastic component, the accidents preserved by high-fidelity reproduction.

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DNA polymerase is an enzyme. Its job is to assist a DNA strand in copying itself. It itself is a protein, configured out of amino acids and manufactured on the instructions of the DNA. So here’s DNA controlling its own replication. DNA polymerase is now on sale at your local biochemical supply house. There’s a laboratory technique, polymerase chain reaction, which unzips a DNA molecule by changing its temperature; the polymerase then helps each strand to reproduce. Each of the copies is in turn unzipped and replicates itself.¹⁶ At every step in this repetitive process, the number of DNA molecules doubles. In forty steps there are a trillion copies of the original molecule. Of course, any mutation happening along the way is also reproduced. So polymerase chain reactions can be used to simulate evolution in the test tube.* Something similar can be done for other nucleic acids:

In the test tube before you is another kind of nucleic acid—this one single-stranded. It’s called RNA (ribonucleic acid). It’s not a double helix and does not have to be unzipped to make a copy of itself. The strand of nucleotides may loop around to join itself, tail in mouth, a molecular circle. Or it may have hairpin or other shapes. In this experiment it’s sitting mixed with its fellow RNA molecules in water. There are other molecules added to help it along, including nucleotide building blocks for making more RNA. The RNA is coddled, jollied, handled with kid gloves. It’s extremely finicky and will do its magic only under very specific conditions. But magic it does. In the test tube not only does it make identical copies of itself, but it also moonlights as a marriage broker for other molecules. Indeed, it performs even more intimate services, providing a kind of platform or marital bed for oddly shaped molecules to join together, to fit into one another. It’s a jig for molecular engineering. The process is called catalysis.

This RNA molecule is a self-replicating catalyst. To control the chemistry of the cell, DNA has to oversee the construction of factotums—a different class of molecules, proteins, which are the catalytic machine tools we’ve been discussing above. DNA makes proteins because it can’t catalyze on its own. Certain kinds of RNA, though, can themselves serve as catalytic machine tools.¹⁷ Making a catalyst or being a catalyst gives you the biggest return for the smallest investment: Catalysts can control the production of millions of other molecules. If you make a catalyst, or if you are a catalyst—the right kind of catalyst—you have a long lever arm on your destiny.

Now in these laboratory experiments, which are being carried out in our time, imagine many generations of RNA molecules more or less identically replicating in the test tube. Mutations inevitably occur, and much more often than in DNA. Most of the mutated RNA sequences will leave no, or fewer, copies, again because random changes in the instructions are rarely helpful. But occasionally a molecule comes into existence that aids its own replication. Such a newly mutated RNA might replicate faster than its fellows or with greater fidelity. If we were uncaring about the fates of individual RNA molecules—and while they may arouse feelings of wonder, they seldom elicit sympathy—and wished only for the advancement of the RNA clan, this is just the kind of experiment we would perform. Most lines would perish. A few would be better adapted and leave many copies. These molecules will slowly evolve. A self-replicating, catalytic RNA molecule may have been the first living thing in the ancient oceans about 4 billion years ago, its close relative DNA being a later evolutionary refinement.

In an experiment with synthetic organic molecules that are not nucleic acids, two closely related species of molecules are found to make copies of themselves out of molecular building blocks provided by the experimenter. These two kinds of molecules both cooperate and compete: They may aid each other’s replication, but they are also after the same limited pool of building blocks. When ordinary visible light is made to shine on this submicroscopic drama, one of the molecules is observed to mutate: It changes into a somewhat different molecule that breeds true—it makes identical copies of itself, and not its pre-mutation ancestor. This new variety, it turns out, is much more adept at replicating itself than the other two hereditary lines. The mutant line rapidly out-competes the others, whose numbers precipitously fall.¹⁸ We have here, in the test tube, replication, mutation, replication of mutations, adaptation, and—we do not think it is too much to say—evolution. These are not the molecules that make us up. They are probably not the molecules involved in the origin of life. There may well be many other molecules which reproduce and mutate better. But what prevents us from calling this molecular system alive?

Nature has been performing similar experiments, and building on its successes, for 4 billion years.

Once even crude replication becomes possible, an engine of enormous powers has been let loose into the world. For example, consider that primitive organic-rich ocean of the Earth. Suppose we were to drop a single organism (or a single self-replicating molecule) into it, considerably smaller than a contemporary bacterium. This tiny being divides in two, as do its offspring. In the absence of any predators and with inexhaustible food supplies, their numbers would increase exponentially. The being and its descendants would take only about one hundred generations to eat up all the organic molecules on Earth. A contemporary bacterium under ideal conditions can reproduce once every fifteen minutes. Suppose that on the early Earth the first organism could reproduce only once a year. Then in only a century or so, all the free organic matter in the whole ocean would have been used up.

Of course, long before that, natural selection would be brought to bear. The genre of selection might be competition with others of your kind—for example, for foodstuffs in an ocean with dwindling stocks of preformed molecular building blocks. Or it might be predation—if you don’t look out, some other being will mug you, strip you down, pull you to pieces, and use your molecular parts for its own ghastly purpose

Major evolutionary advance might take considerably more than one hundred generations. But the devastating power of exponential replication becomes clear: When the numbers are small, organisms may only infrequently come into competition; but after exponential replication, enormous populations are produced, stringent competition occurs, and a ruthless selection comes into play. A high population density generates circumstances and elicits responses different from the more friendly and cheerful lifestyles that pertain when the world is sparsely populated.

The external environment is continuously changing—in part because of the enormous population growth when conditions are favorable, in part because of the evolution of other organisms, and in part because of the ticking geological and astronomical clockwork. So there’s never such a thing as a permanent or final or optimum adaptation of a lifeform to “the” environment. Except in the most protected and static surrounds, there must be an endless chain of adaptations. However it feels on the inside, it might very well be described from the outside as a struggle for existence and a competition between adults to ensure the success of their offspring.

You can see that the process tends to be adventitious, opportunistic—not foresighted, not with any future end in view. The evolving molecules do not plan ahead. They simply produce a steady stream of varieties, and sometimes one of the varieties turns out to be a slightly improved model. No one—not the organism, not the environment, not the planet, not “Nature”—is mulling the matter over.

This evolutionary shortsightedness can lead to difficulties. It might, for example, cast aside an adaptation that is perfectly suited for the next environmental crisis a thousand years from now (about which, of course, no one has a glimmering). But you have to get from here to there. One crisis at a time is life’s motto.

ON IMPERMANENCE

If we lived forever, if the dews of Adashino never vanished, if the crematory smoke on Toribeyama never faded, men would hardly feel the pity of things. The beauty of life is in its impermanence. Man lives the longest of all living things … and even one year lived peacefully seems very long. Yet for such as love the world, a thousand years would fade like the dream of one night.

KENKO YOSHIDA, Essays in Idleness (1330–1332)¹⁹

* The silent “gh” in such English words as thought and height, or the silent “k” in knife or knight, were likewise once sounded out, but today are little more than a vestige of the evolution of language Something similar is true for the circumflex and cedilla which are in the course of being phased out in French, and for recent simplifications of Chinese and Japanese The nonfunctional genetic sequences, however, are not just a few letters here and there, but reams of obsolete and/or garbled information—something like a confused account in ancient Assyrian on how to manufacture chariot axles, set in more recently generated nonsense information* Before the method of radioactive dating was invented, the physicists simply had no way to get the timescales right Darwin’s son George became a leading expert on tides and gravity—in part to refute the claim that the history of the Moon proved the Earth to be too young for much biological evolution Several different radioactive clocks found within samples from the Earth, the Moon, and the asteroids; the abundance of impact craters on nearby worlds; and our understanding of the evolution of the Sun all independently and definitively point to an Earth about 4.5 billion years old.The technique is also being used to take tiny quantities of DNA from the remains of ancient organisms—bacteria from the gut of a preserved mastodon, for example—and make enough copies so they can be studied It has even been proposed that preserved somewhere in amber may be the remains of a bloodsucking insect that bit a dinosaur, from which we may one day learn about dinosaur biochemistry or even—this point is keenly debated—reconstruct, and in a way resuscitate, dinosaurs extinct for 100 million years In the best of circumstances, this does not seem to be a prospect for the near future

Chapter 6

US AND THEM

Let there be no strife, I pray thee, between me and thee … for we be brethren.

Genesis 13:8

There are no compacts between lions and men.

HOMER, The Iliad¹

Whether there were many instances of the origin of life on Earth or only one is a deep and perhaps impenetrable mystery. For all we know, there may have been millions of dead ends and false starts, unmourned ancient genealogies snuffed out as new ones arose. But it seems very clear that there’s only one hereditary line leading to all life now on Earth. Every organism is a relative, a distant cousin, of every other. This is manifest when we compare how all the organisms on Earth do business, how they’re built, what they’re made of, what genetic language they speak, and especially how similar their blueprints and molecular job orders are. All life is kin.

In our imagination, let’s cast our eyes back to the earliest organisms. They could not have been so purebred and pampered a line of self-replicating molecules as contemporary DNA or RNA—superbly efficient in the replication and proofreading of their messages, but reproducing only under the meticulously controlled conditions upon which modern organisms insist. The first living things must have been rough-and-ready, slow, careless, inefficient—just barely good enough to make crude copies of themselves. Good enough to get started.

At some point, probably extremely early on, organisms had to be more than a single molecule, no matter how talented that molecule might be. For very precise instructions to be followed to the letter, for reproduction to occur with high fidelity, other molecules were needed—to scour building blocks from the adjacent waters and bend them to your purpose; or, like DNA polymerase, to be midwife in the replication process; or to proofread a newly minted set of genetic instructions. But it did you no good if such accessory molecules kept drifting out to sea. What you needed was a kind of trap to keep useful molecules captive. If only you could surround yourself with a membrane that, like a one-way valve, lets in the molecules you need and doesn’t let them out … There are molecules that do that—that, for example, are attracted to water on one side of them, but are repelled, absolutely revolted by water on the other. They’re common in Nature. They tend to make little spheres. And they’re the basis of cell membranes today.

The earliest cells, although able simultaneously to multiply and divide, could not possibly have been conscious in anything like the sense that humans are. Still, they had certain behavioral repertoires. They knew how to copy themselves, of course; how to convert molecules from the outside, different from them, into molecules on the inside that were them. They were preoccupied with improvements in the precision of replication and the efficiency of metabolism. Some could even distinguish sunlight from darkness.

Breaking down molecules taken in from the outside, that is, digesting food, can be done safely only in a step-by-step fashion, each step controlled by a given enzyme, and each enzyme controlled by its own ACGT sequence, or gene. The genes then must work together in exquisite harmony; otherwise none of them will propagate into the future. In digesting a molecule of sugar, for example, the meticulously choreographed action of dozens of enzymes is required, each picking up where the last one left off, each enzyme manufactured by a particular gene. The defection of a single gene from the common enterprise can be fatal to all of them. An enzyme chain is only as strong as its weakest link. On this level, genes are single-mindedly dedicated to the general welfare of their tribe.

Early enzymes had to be discriminating; they had to take care not to decompose the very similar molecules that constituted the lifeform they were part of. If you digest yourself—the sugars that are part of your DNA, say—you don’t leave many descendants. If you don’t digest others—convenient repositories of organic raw materials and finished molecular goods—you may not leave many descendants either. Cells of 3.5 billion years ago must have possessed some knowledge of the difference between “me” and “you.” And “you” was more expendable than “me.” A dog-eat-dog or, at least, a microbe-eat-microbe world. But wait …

A time came—perhaps 2 or 3 billion years ago—when one being could incorporate another whole. One would nuzzle up to the other, the cell walls or membranes would pucker, and the littler fellow would find itself inside the bigger. Attempts at digestion, with varying success, doubtless ensued. Suppose you are a largish one-celled organism in the primitive oceans who in this way gobbles up some photosynthetic bacteria, tiny specialists who know how to use sunlight, carbon dioxide, and water to manufacture sugars and other carbohydrates. You’ll leave more descendants if you’re better than your competitors in acquiring sugar (a key building block needed to replicate your genetic instructions and to power all you do).

But suppose also that these ingested bacteria—the latest, sturdy, rustproof models—do not succumb to your digestive enzymes. For all they know, they’ve found their way into a molecular Garden of Eden. You protect them from many of their enemies; because you’re transparent, sunlight shines into you for them; and there’s plenty of water and carbon dioxide around. So inside you, the bacteria continue to do their photosynthetic magic. Some sugars leak out of them, for which you are grateful. Some of them die and their interior molecules spill out, available for your use. Others of them flourish and multiply. When the time comes for you to reproduce, some of them wind up inside your offspring. Not yet de jure (because nothing of this arrangement is yet encoded in the nucleic acids), but certainly de facto, an accommodation has been reached between your descendants and theirs.²

It’s a good deal for both parties. They open up a little fast-food concession stand inside your body, at hardly any cost to you. You provide a stable and protected environment for them (so long as you take care not to digest your guests). After many generations have passed, you’ve evolved into quite a different kind of being, with little green photosynthetic power plants inside of you reproducing when you do, clearly part of you, but also clearly different. You’ve become a partnership. This seems to have happened a half dozen times or more in the history of life, each instance leading to a different major group of plants.³

Today every green plant contains such inclusions, called chloroplasts. They are still rather like their free-living one-celled bacterial ancestors. Nearly every bit of green in the natural world is due to chloroplasts. They are the photosynthetic engines of life. We humans pride ourselves on being the dominant lifeform on this planet, but these tiny beings—unobtrusive, the perfect guests—are in a sense running the show. Without them, almost all life on Earth would die.

They’ve made many concessions to their hosts. They’ve achieved a working mutual assistance pact of long duration, called symbiosis. Each partner relies on the other. Still, the chloroplasts are recognizably a latecomer to the cell. The clearest sign of their separate origin is the difference between their nucleic acids and the plant cell’s own nucleic acids, although long ago they had a common ancestor. The signature of their separate, early evolution before joining forces is plain. The original chloroplast seems to have come from a photosynthetic bacterium very much like those living in stromatolite communities today.⁴

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You look at these little one-celled beings under the microscope and you’re struck by their apparent self-assurance. They seem to know with such certainty what they’re about. They swim toward the light or attack prey or struggle to escape from predators. Because they’re transparent, you can see their internal parts, the DNA-driven protoplasmic clockwork, making them go. Their ability to transmute the food they come across into the molecules they need—for energy, for parts, for reproduction—is downright alchemical. The plants among them convert air and water and sunlight into themselves not haphazardly, but according to specific recipes, the mere writing out of which would fill many volumes on organic chemistry and molecular biology. Each of them is only one cell; no organs, no brains, no snappy conversation, no poetry, no higher spiritual values—and yet they can do, without any apparent conscious awareness, far more along these chemical lines than can our vaunted technology.

And there’s something else they can do that we can’t. They can live forever. Or nearly so. These asexual, one-celled organisms reproduce by fission—not nuclear, but biological fission. A little furrow, an indentation, appears and ripples down the middle of the organism. The internal parts are divided more or less evenhandedly, and suddenly we have before us not one organism but two. It has split in half. We now see two smaller beings, each nearly identical to its single parent and genetically the same, identical twins. Quickly, each grows to adult size. Later, the process continues. Except for the odd mutation, remote descendants are perfect facsimiles of their ancestors. In a real sense, the ancestors never died. At no point along the way are there corpses of aged parents. If there are no accidents, no drop of poison released by other microbes, no extremes of temperature, no running out of food, no encounters with a big, bad amoeba, then they continue to live on, the natural slow falling to pieces of their organic body parts mitigated or reversed by their frequent reproduction.

These ubiquitous, invisible, and most humble organisms are immortal—at least by human standards. There are enough natural vicissitudes that they cannot go for too long without encountering one disaster or another. But at least some of them live for more lifetimes than the most extravagant and credulous disciple of reincarnation or “multiple life regression” ever imagined. The current official record is held by a laboratory stock of the one-celled organism called Paramecium, familiar to high-school biology students. Eleven thousand successive generations of paramecia have been carefully nurtured in the test tube, with no senescence or aging apparent.⁵ (In humans, eleven thousand generations would take us all the way back to the dawn of our species.) Except for the slow buildup of mutations, the paramecia at the end of this train of generations were genetically identical to those at the beginning. In a way, the longing for immortality, so characteristic of Western civilization, is a longing for the ultimate regression into the past—to our single-celled ancestors in the seething primeval ocean.

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We have, so far in this saga, not come within a billion years of our epoch. But even in so remote a time, many of the major themes and variations of present life on Earth had been clearly articulated. Some of the fossils of that time are indistinguishable in form from some contemporary organisms, the stromatolites being the most famous example. Others are wildly different. There has surely been a growing biochemical sophistication over the aeons, in enzyme chemistry, fidelity of DNA replication, and many other matters that must be indetectable in mere fossils; still, it seems astonishing that any organism should be unchanged—even if just in its gross anatomy—over 3.5 billion years. We can recognize again a stolid conservatism in living things. And yet quick and fundamental change sometimes happens. The picture that emerges is of a rich menu of candidate adaptations offered up by mutation for consideration by natural selection. But only under sentence of death (or what in the evolutionary perspective is the same thing, the threat of no descendants) are these mutational propositions seriously taken up and tried out. Except for cosmetic touches, new kinds of life are ordinarily discouraged. Change is grudging.

You can see the same classes of molecules used over and over again for completely different purposes. Today, for example, the same complex organic molecule is used, with minor variations, as the green pigment that sips sunlight in plants; as the red pigment that carries oxygen through the bloodstreams of animals; as the agent that makes shrimps and flamingos pink; and in a widely used enzyme that helps wheedle energy safely out of sugar. The energy is banked, against future need, in molecules nearly identical to the nucleotides A, C, G, and T of the genetic code. While these are molecules of breathtaking versatility, their repeated use and recycling reveals parsimony as a way of life.

It’s as if, for every million dyed-in-the-wool conservative organisms, there’s one radical who’s out to change things (although usually very small things); and for every one of the radicals, only one in a million actually knows what it’s talking about—providing a significantly better survival plan than the one currently fashionable. And yet the evolution of life is determined by these revolutionaries.

Given enough food, microorganisms reproduce so quickly that they can evolve in the time between putting them on a shelf for storage and retrieving them for further examination. The speed with which bacteria “acquire” resistance to antibiotics cautions restraint about prescribing them too frequently. The antibiotic does not usually induce adaptive mutations; instead, it acts as a fierce agent of selection, killing off all bacteria except a favored few that, by chance, are immune to the medicine—a strain that earlier, for other reasons, might not have competed successfully with its fellows. The fact that bacteria quickly evolve resistance to antibiotics (or insects to DDT) reflects the enormous diversity of forms and biochemistries always churning subsurface in the microbial world. There is a continuing war of measure and countermeasure, raging between host and parasite—in this case, between the pharmaceutical companies, generating new antibiotics, and the microbes, generating new resistant strains to replace their more vulnerable ancestors.

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Well-developed even by 3.5 billion years ago, we’ve argued, was the distinction between the inside and the outside, me and you, us and them, a rudimentary consciousness of self. If you’re in the habit of eating organic molecules dissolved in the primeval oceans, you’re also used to eating the molecules that make up other beings; after all, they’re the same molecules. But then you’d better take care you don’t eat yourself. You may not have pity or compassion for other organisms. That’s probably not how a microbe views the world. But you must make some fine distinctions. You may lack sentimental feelings for your chloroplasts, but if you digest them, you’re in trouble. If the distinction is too difficult for you to make—if you can’t figure out the difference between “me” and “you,” if you can’t control your digestive enzymes—then you’ll leave fewer offspring, or none. There’s not yet any thinking through. There may be no feelings of any sort. Nevertheless, organisms are beginning to behave as if they had wants, needs, preferences, emotions, drives, instincts.

If you’re living in a group, it will help neither them nor you if you set about eating your fellows. You may be a ruthless, implacable predator, but you must also be a pushover for your relatives and neighbors. So all of you may suffuse your outer membranes with a chemical that serves for species recognition. When you taste this molecule emanating from another microbe, you become very affable. “Friend,” the chemical says. “Sister.” Other chemicals carry different information. Some bacteria routinely produce their own chemical warfare agents, antibiotics that are harmless to themselves and others of their own strain, but deadly to bacteria of different strains, foreigners. A delicate balance has evolved between hostility to the outside group and cooperation with the inside group. Them and us. The first intimations of xenophobia and ethnocentrism evolved early.

Big carnivores enjoy their work. (One-celled carnivores may also.) They don’t hunt because they have an academic knowledge of nutrition: They hunt, it seems, because hunting is a delight; because stalking, chasing, maiming, killing, dismembering, and eating are the pleasures of life; because the urge to do so is irresistible. Fat cats and lazy dogs, stuffed with hors d’oeuvres, their gustatory needs provided for, nevertheless sometimes heed an ancient call, and the urban pet owner finds a dead mouse or pigeon proudly laid at her feet. The machinery is hardwired; the computer is preprogrammed. An appropriate stimulus can set it off. Its hunting proclivities finding no other outlet, the dog fetches a stick or a Frisbee, and the cat swats at a cobweb or pounces on a ball of wool.

Even so formidable and elegant an example of hardwiring as a cat hunting a rat, though, depends a great deal on past experience. In a set of classic experiments, the psychologist Z. Y. Kuo⁶ showed that almost all kittens who witness their mother killing and eating a rodent eventually do so themselves. However, when kittens are raised in the same cage with a rat, never seeing any other rat, and never seeing a cat kill a rat, then they almost never kill rats themselves. When kittens have a rat for a littermate and also witness their mothers killing rats outside the cage, about half of them learn to kill—but they tend to kill only the kinds of rat they had seen their mothers kill, and not the kinds that they grew up with. Finally, when kittens are given an electric shock each time they see a rat, they soon learn not to kill rats—indeed, to run in terror from them.

So even such basic hardwiring as the predation program in cats is malleable. Of course humans are not cats. But we might be tempted nevertheless to guess that childhood experience, education and culture can do much to mitigate even deep inborn proclivities.

Starting with the early microbes, the behavioral machinery for hunting and escaping, and for altering these inclinations according to experience, were developing. Predators slowly evolved into larger, faster, and smarter models, with new options (for example, feinting). Potential prey likewise evolved larger, faster, and smarter models with other options (for example, “playing dead”)—because those who didn’t were more often eaten. Many strategies were devised; the successful ones were retained: protective camouflage, body armor, ink or sprayed noxious liquids to cover an escape, poisonous stings, and exploiting niches where there were as yet no predators—a shallow hole in the ocean floor, perhaps, or a sanctuary in a seashell, or a homestead on an untenanted island or continent. Another strategy was simply to produce so many progeny that at least some survive. Again, no potential prey plans such adaptations; it’s just that after a while the only prey left are the ones who act as if they had planned it all out. No matter how fine your intentions, how benign and contemplative your inclinations, if you’re potential prey you’re forced by natural selection into adopting countermeasures.

By around 600 million years ago, many multicellular animals started walling themselves in, surrounding their soft bodies with shells and carapaces, learning to do small-scale civil engineering, building defenses out of silicate and carbonate rock. Lifestyles of clams, oysters, crabs, lobsters, and many other armored animals, some now extinct, developed then. Since, with rare exceptions, soft parts of dead animals decompose quickly and hard parts or their imprints survive longer—sometimes even long enough to be noticed by paleontologists hundreds of millions of years in the future—the evolution of body armor made these distant creatures knowable to their remote collateral relatives.

The warfare between predator and prey extends to the plant kingdom as well. Plants load themselves with poisons to discourage animals from eating them. The animals evolve detoxification chemistry and special organs—the liver, most prominently—to keep pace with the plants. What we like about coffee, for example, are the toxins that have evolved to deter insects and small mammals from consuming coffee beans.⁷ But we have sophisticated livers.

Of course, predators need not be bigger than their prey. Disease microbes can be formidable predators—not only attacking and eventually killing the organisms that bear them, but also taking over their hosts, changing their behavior to spread the disease microorganisms to other hosts. One of the most striking examples is the rabies virus. On being injected into the bloodstream of a placid, people-loving dog, they head straight for the limbic system of the dog’s brain, where the control buttons for rage reside. There, they set about converting the poor animal into a marauding, snarling, vicious predator that now bites the hand that feeds it. Rabid animals are afraid of no one. At the same time, other rabies viruses are dispatched to inactivate the nerves for swallowing, to put the saliva-manufacturing machinery into overdrive, and to invade the saliva in huge numbers. The dog is furious, although it has no idea why. A pawn of the viruses within it, it’s helpless to resist the impulse to attack. If the attack is successful, the viruses in the dog’s saliva enter the bloodstream of the victim through the lesion or laceration, and then set about taking over this new host. The process continues.

The rabies virus is a brilliant scenarist. It knows its victims, and how to pull their strings. It circumvents their defenses—infiltrating, outflanking, accomplishing a coup d’état within beings so much larger, you might have thought them invulnerable.*

In influenza or the common cold, it’s not an incidental adjunct of the infection that we cough and sneeze, but rather central to the proliferation of the virus responsible, and under its control. Some other examples of microbes pulling the strings:A toxin produced by the cholera bacterium interferes with reabsorption of liquid from the bowel, thus resulting in profuse diarrhea that spreads the infection … Tobacco mosaic virus causes its host to enlarge cell membrane pores so that the virus can pass through to uninfected cells … A lancet fluke is effectively transmitted from ants to sheep because it induces an infected ant to climb to the top of a blade of grass and grab on, never to let go. A fluke causes snail hosts to crawl to exposed sections of beach where they are easy prey for the gulls that are the next host in the life cycle.⁸

Over many generations of life-and-death interaction between predator and prey, a kind of permanent arms race is established. For every offensive advance there is a defensive counter, and vice versa. Measure and countermeasure. Rarely does anyone become safer.

Some prey grow up together, swarm together, school together, herd together, flock together. There’s safety in numbers. The strongest can be brought in to intimidate or defend against a large predator. The attacker can be mobbed by the entire group of prey. Lookouts can be posted. Danger calls can be agreed upon and coordinated, escape strategies chosen. If the prey are quick, they can dart before the predator, outrace and confuse it, or draw it away from especially vulnerable members of the group. But there is also a selective advantage for cooperation among the predators—for example, one group flushing prey toward another that lies in ambush. For prey and predator alike, community life may be more rewarding than solitude.

To play the escalating evolutionary game of predator and prey, complex behavioral repertoires are eventually needed. Each must detect the other at a distance, and a high premium is established on supplanting local senses such as touch and taste by more long-range senses such as smell, sight, hearing and echo-location. A talent for remembering the past develops in the heads of small animals. Some simple cases of contingency planning, imagining what your response might be to a variety of circumstances (“I’ll do Z if it does A; I’ll do Y if it does B”) may already have been in the genes; but expanding that talent into more complex branched contingency trees, new logic for future needs, greatly aids survival. Indeed, to find and eat anyone—even organisms that take no evasive action—requires, especially when the supply is sparse, a predator to know a great deal.

Basing all your behavior on a pre-programmed set of instructions written in the ACGT language places no undue demands—as long as the environment is the one you were evolved for. But no pre-programmed set of instructions, no matter how elaborate, no matter how successful in the past, can guarantee continuing survival in the face of rapid environmental change. Evolution through natural selection involves only the most remote, generalized, almost metaphorical kind of learning from experience. Something else is needed. When you hunt food; when mobility is high and organisms can roam among very different environments; when social relations with your own kind as well as predator/prey interactions become intricate; when you’re required to process enormous amounts of information about the external world—at such times, especially, it pays to have a brain. With a brain you can remember past experiences and relate them to your present predicament. You can recognize the bully who picks on you and the weakling you can pick on, the warm burrow or protected rock crevice to which you have safely fled before. Opportunistic scenarios for gathering food, or hunting, or escaping may occur to you at a critical moment. Neural circuitry develops for data processing, pattern recognition, and contingency planning. There are premonitions of forethought.

The style of evolution of brains—and much else—is not usually a matter of steady progression. Instead, the fossil record speaks of short periods of rapid and radical evolution, punctuating immense periods of time in which the sizes of brains hardly change at all. This seems true from the evolution of the earliest mammals to the evolution of our own species.⁹ It’s as if there’s a rare concatenation of events—perhaps changes in the DNA sequence and the external environment together—that provides an adaptive opportunity. The new environmental niches are quickly filled, and for a long time subsequent evolution is devoted to consolidating the gains. Major advances in neural architecture—in the brain’s ability to process data, to combine information from different senses, to improve its model of the nature of the outside world, and to think things through—may be very expensive. For many animals these are such broad-gauge talents, requiring so many separate evolutionary steps, that the major benefits may come only in the far future, while evolution is transfixed by the here-and-now. Nevertheless, even tiny advances in thinking are adaptive. Spurts in brain size have happened sufficiently often in the history of life for us to conclude, from this fact alone, that brains are useful to have around.

Feeling, in mammals at least, is mainly controlled by lower, more ancient parts of the brain, and thinking by the higher, more recently evolved outer layers.¹⁰ A rudimentary ability to think was superimposed on the pre-existing, genetically programmed behavioral repertoires—each of which probably corresponded to some interior state, perceived as an emotion. So when unexpectedly it is confronted with a predator, before anything like a thought wells up, the potential prey experiences an internal state that alerts it to its danger. That anxious, even panicky state comprises a familiar complex of sensations, including, for humans, sweaty palms, increased heartbeat and muscle tension, shortened breath, hairs standing on end, a queasiness in the belly, an urgent need to urinate and defecate, and a strong impulse either for combat or retreat.* Since in many mammals fear is produced by the same adrenaline-like molecule, it may feel pretty much the same in all of them. That’s at least a reasonable first guess. The more adrenaline in the bloodstream, up to a certain limit, the more fear the animal feels. It’s a telling fact that you can artificially be made to feel this precise set of sensations just by being injected with some adrenaline—as sometimes happens at the dentist’s (to shorten the clotting time of your blood, another useful adaptation when you’re confronting a predator. Of course you may also be generating some of your own adrenaline at the dentist’s.) Fear has to have an emotion tone about it. It has to be unpleasant.

If the predator’s eye/retina/brain combination is geared especially to detect motion, the prey often have, in their repertoire of defenses, the tactic of standing frozen, stock-still, for long periods of time. It’s not that squirrels, say, or deer understand the physiology of their enemies’ visual systems; but a beautiful resonance between the strategies of predator and prey has been established by natural selection. The prey animal may run; play dead; exaggerate its size; erect its hairs and shout; produce foul-smelling or acrid excretions; threaten to counterattack; or try a variety of other, useful survival strategies—all without conscious thought. Only then may it notice an escape route or otherwise bring into play whatever mental agility it possesses. There are two nearly simultaneous responses: one, the ancient, all-purpose, tried-and-true, but limited and unsubtle hereditary repertoire; and the other, the brand-new, generally untried intellectual apparatus—which can, however, devise wholly unprecedented solutions to urgent current problems. But large brains are new. When “the heart” counsels one action and “the head” another, most organisms opt for heart. The ones with the biggest brains more often opt for head. In either case, there are no guarantees.

——

Obliged to accommodate to every twist and turn in the environment they depend upon, living things evolve to keep up. By painstaking, small steps, through the passage of immense vistas of geological time, via the deaths of innumerable slightly maladapted organisms, uncomplaining and unlamented, life—in its interior chemistry, external form, and menu of available behavior—became increasingly complex and capable. These changes, of course, are reflected in (indeed, caused by) a corresponding elaboration and sophistication of the messages written in the ACGT code, down there at the level of the gene. When some splendid new invention comes along—bony cartilage as body armor, say, or the ability to breathe oxygen—the genetic messages responsible proliferate across the biological landscape as the generations pass. At first no one has these particular sequences of genetic instructions. Later, large numbers of beings all over the Earth live by them.

It’s not hard to imagine that what’s really going on is an evolution of genetic instructions, battles between the genetic instructions of competing organisms, genetic instructions calling the shots—with the plants and animals little more, or maybe nothing more, than automata. The genes arrange for their own continuance. As always, the “arranging” is done with no forethought; it’s merely that those beautifully coordinated genetic instructions that, by chance, give superior orders to the living thing they inhabit make more living things motivated by the same instructions.

Think again of the changes in our behavior caused by the incursion of a rabies or an influenza virus (made of nucleic acids wearing a coat of protein). Surely much more profound control over us is exercised by our own nucleic acids. When you strip away the fur and feathers, the physiological and behavioral particularities, life is revealed to be the preferential replication of some ACGT messages rather than other, competing messages; a conflict of genetic recipes; a war of words.

In this perspective,¹¹ it’s the genetic instructions that are being selected and that are evolving. Or you might with nearly equal justice say it’s the individual organisms, under the tight control of the genetic instructions, that are being selected and that are evolving. There is no room here for group selection—the natural and attractive idea that species are in competition with one another, and that individual organisms work together to preserve their species as citizens work together to preserve their nation. Acts of apparent altruism are instead attributed chiefly to kin selection. The mother bird slowly flutters from the fox, one wing bent as if broken, in order to lead the predator away from her brood. She may lose her life, but multiple copies of very similar genetic instructions will survive in the DNA of her chicks. A cost-benefit analysis has been made. The genes dictate to the outer world of flesh and blood with wholly selfish motives, and real altruism—self-sacrifice for a non-relative—is deemed a sentimental illusion.¹²

This, or something quite like it, has become the prevailing wisdom in the field of animal (and plant) behavior. It has considerable explanatory power. At the human level it helps to explain such varied matters as nepotism and the fact that foster children are much more likely (in America, for example, about a hundred times more likely¹³) to be fatally abused than children living with their natural parents.

The cooperation of the cells in stromatolites and other colonial organisms can be understood as selfish at the level of the gene, since they’re all close relatives. Cooperation of the chloroplast and the cell with which it forms a symbiotic attachment—is this selfish? The cell that eats its chloroplasts is at a competitive disadvantage. It refrains from eating them not because it has even a glimmer of altruistic feeling for the chloroplasts, but because it’s dead without them. It forgoes the pleasures of a chloroplast meal for a substantial future benefit. It exercises restraint on short-term, selfish behavior. It practices impulse control. Selfishness still prevails, but we are made aware of the distinction between short- and long-term selfishness.

For most social animals, and for obvious reasons, the animals you grow up with tend to be close relatives. So if you cooperate, if you show what superficially might seem like altruism, it’s naturally directed toward close kin and can therefore be explained as kin selection. An organism might forego its own replication, for example, and devote its life to improving the chances of the survival and reproduction of close relatives—those with very similar DNA sequences. If all that counts is which sequences will be widely represented in the life of the future, those species with a flair for altruism might do well. They can help ensure that much of their genetic information is passed on, even if none of their atoms wind up in the bodies of the next generation.¹⁴

The geneticist R. A. Fisher described heroism as a predisposition inclining its bearer toward “an increased probability of entering an occupation not easily to be reconciled with family life.” Nevertheless, Fisher argued, heroism—in humans or in other animals—might carry a selective advantage by preserving the very similar genetic sequences of close relatives, enabling such sequences to be passed on to future generations. This is one of the first clear articulations of kin selection. Parents sacrificing themselves for a child can be understood on similar grounds. The hero or the devoted parent will be doing simply what feels “right,” without attempting any calculus of benefit versus risk to the gene pool. But the reason it feels “right,” Fisher proposed, is that extended families characterized by conscientious parenting and heroes aplenty will tend to do very well.*

Animals may be willing to make real sacrifices for close relatives, but not for more distant kin. Think of it this way: Imagine sleeping soundly at night, knowing that your children are starving, homeless, or gravely ill. For almost all of us, it would be unthinkable. But forty thousand children die each day of easily preventable hunger, neglect, or disease. Institutions such as the United Nations Children’s Fund are in place that could save these children—with innoculations against illness, with a few cents a day worth of salts and sugar. But the money is unavailable. Other needs are deemed more pressing. The children continue to die while we sleep well. They are far away. They are not ours. Now tell us you don’t believe in the reality of kin selection.

Still, if you find yourself among others of your own species who are not your near kin, surely it is to your advantage to cooperate against a common enemy. You can draw upon behavior evolved for kin selection in order that a group of animals not closely related can cohere and survive.* And if altruism is one of your talents, you might find yourself practicing it even on animals of another species. Dogs are known to risk their lives to save humans—surely no close relatives. Nor does the hope of future reward explain their behavior.

How are we to understand well-attested cases of dolphins saving drowning humans by repeatedly nuzzling them up to the surface and pushing them toward shore? Is the dolphin unable to distinguish the thrashing human from an infant dolphin in trouble? This is highly unlikely; dolphins are discerning observers. What about cases of abandoned or strayed human infants being raised by wolf mothers that have lost their pups, or birds of a different species brooding cuckoo eggs? Why do drivers swerve to avoid hitting a dog on the road, although they thereby put their own children in the back seat at increased risk? What about youngsters dashing back into the burning house to rescue the cat? Such cases of courage and care directed to other species may derive from a misdirected kin selection, but they do happen and they do save lives. Shouldn’t we then expect to find altruistic behavior much more frequently directed toward other members of the same species, even if they’re not close relatives?

Consider two groups, one composed of unrelentingly selfish individualists, the other of solid citizens who are occasionally willing to sacrifice themselves for (even distantly related) others. Against a common enemy, can we not imagine circumstances in which the latter group fares better than the former? Obvious disadvantages also accrue to a community of strict altruists constantly throwing their lives away in order to benefit total strangers. Such a group would not last long—if only because any tendency toward selfishness would quickly spread.

What if there’s a critical size for the group to work? When membership is below some rough threshold, certain functions of the group begin to fail. For example, the bigger the group, the better huddling together for warmth works,¹⁵ or mobbing a predator;¹⁶ and below a certain size, group benefits become increasingly unavailable. It’s not hard to imagine wholly selfish genes that cause defections from community service—a refusal to mob a predator, say, because it might be dangerous. If these genes proliferate, the point will be reached where almost nobody has the gumption to mob, and the danger posed to everyone by predators has increased. Thus, for longer-term reasons that are selfish at the level of the genetic instructions, short-term altruism may be adaptive, and might be selected for—even if the members of the group are not near relatives. In closely knit communities, individual selection and what looks very much like group selection are both elicited.

Many examples thought to demonstrate group selection have, with an almost maddening ingenuity, been explained at least equally well by a new school of biologists and game theorists. Some explanations seem quite plausible, but not all. For example, when a predator threatens a group of Thomson gazelles, one or two may leap in conspicuous high arcs near the predator. This is called stotting. The group selectionist view is straightforward: The individual calls attention to itself and risks being eaten in order to save the group. (But suppose stotting were never invented; could the predator eat more than one Thomson gazelle anyway? Compared to other species of gazelles ignorant of stotting, are fewer eaten thanks to stotting?) The prevailing individual selectionist view is that the stotter is advertising its own gymnastic abilities and reminding the predator that less athletic gazelles are easier to eat. It stots for crassly selfish reasons.¹⁷ (But then why don’t most Thomson gazelles stot when stalked? Why doesn’t such selfishness spread through the herd? Does the predator in fact turn its attention from the stotter to a less conspicuous gazelle?)

Like the classic optical illusions—is it a candelabra, or two faces in profile?—the same data can be understood from two quite different perspectives (although neither may be fully satisfying). Each may have its own validity and utility.¹⁸ Individual selection and group selection must ordinarily go together (or, in scientific speech, be highly correlated); otherwise evolution would never occur. We might argue that individual selection must have some primacy, because you can have individuals without a group, but not vice versa. However there are many animals, primates among them, where the individual cannot survive without the group.

Strict selfishness and strict altruism are, it seems to us, the maladaptive ends of a continuum; the optimum intermediate position varies with circumstance, and selection inhibits the extremes. And if it’s too difficult for the genes to figure out on their own what the optimum mix is for each novel circumstance, might it not be advantageous for them to delegate authority? For this again, brains are needed.

Consider kin selection once more. Never mind the nagging question about how well birds, say, can distinguish uncles from cousins; especially in small groups, it doesn’t much matter—everyone’s a pretty close relative, and kin selection works in a statistical sense, even if you occasionally put yourself on the line for some unrelated neighbor. It makes sense, in terms of the preservation of multiple copies of closely related genetic instructions, to accept a 40% chance of dying to save the life of a sibling (who has 50% of the same genes you have); or a 20% chance to save an uncle or a niece or a grandchild (who share 25% of your genes); or a 10% chance of dying to save the life of a first cousin (who has 12.5% of exactly the same genes that you do). Well, then, what about giving up the means of affording another child in order to preserve the families of many second cousins? What about donating ten percent of your income so a gaggle of third cousins have enough to eat? Might it pay to abstain from a few luxuries so fourth cousins can be educated? What about writing a letter of recommendation for an undistinguished fifth cousin?

Kin selection is also a continuum, and in its arcane calculus some sacrifice must be worthwhile to aid the most far-flung and distant members of your family. But since we are all related, some sacrifice must be justified to save anyone on Earth—and not only those of our own species. Even on its own terms, kin selection extends far beyond close relatives.

Typically, any two members of a small community of primates in the wild have 10 to 15% of their genes in common¹⁹ (and about 99.9% of their ACGT sequences in common, it requiring only a single nucleotide difference to make one gene, composed of thousands of nucleotides, different from another). So any random member of the group is pretty likely to be your parent or child or sibling, uncle, aunt, nephew, niece, or first or second cousin. Even if you can’t distinguish one from the other, it makes good evolutionary sense to make real sacrifices for them—and to accept something like a 10% chance of dying in order to save the life of any one of them.

In the annals of primate ethics, there are some accounts that have the ring of parable. Consider, for example, the macaques. Also known as rhesus monkeys, they live in tightly knit cousins’ clubs.²⁰ Since the macaque you save is statistically likely to share many of your genes (assuming you’re another macaque), you’re justified in taking risks to save it, and a fine discrimination of shades of consanguinity is unnecessary. In a laboratory setting,²¹ macaques were fed if they were willing to pull a chain and electrically shock an unrelated macaque whose agony was in plain view through a one-way mirror. Otherwise, they starved. After learning the ropes, the monkeys frequently refused to pull the chain; in one experiment only 13% would do so—87% preferred to go hungry. One macaque went without food for nearly two weeks rather than hurt its fellow. Macaques who had themselves been shocked in previous experiments were even less willing to pull the chain. The relative social status or gender of the macaques had little bearing on their reluctance to hurt others.

If asked to choose between the human experimenters offering the macaques this Faustian bargain and the macaques themselves—suffering from real hunger rather than causing pain to others—our own moral sympathies do not lie with the scientists. But their experiments permit us to glimpse in non-humans a saintly willingness to make sacrifices in order to save others—even those who are not close kin. By conventional human standards, these macaques—who have never gone to Sunday school, never heard of the Ten Commandments, never squirmed through a single junior high school civics lesson—seem exemplary in their moral grounding and their courageous resistance to evil. Among the macaques, at least in this case, heroism is the norm. If the circumstances were reversed, and captive humans were offered the same deal by macaque scientists, would we do as well?²² In human history there are a precious few whose memory we revere because they knowingly sacrificed themselves for others. For each of them, there are multitudes who did nothing.

——

T. H. Huxley remarked that the most important conclusion he had gleaned from his anatomical studies was the interrelatedness of all life on Earth. The discoveries made since his time—that all life on Earth uses nucleic acids and proteins, that the DNA messages are all written in the same language and all transcribed into the same language, that so many genetic sequences in very different beings are held in common—deepen and broaden the power of this insight. No matter where we think we are on that continuum between altruism and selfishness, with every layer of the mystery we strip away, our circle of kinship widens.

Not from some uncritical sentimentalism, but out of tough-minded scientific scrutiny, we find the deepest affinities between ourselves and the other forms of life on Earth. But compared to the differences between any of us and any other animal, all humans, no matter how ethnically diverse, are essentially identical. Kin selection is a fact of life, and is very strong in animals that live in small groups. Altruism is very close to love. Somewhere in these realities, an ethic may be lurking.

ON IMPERMANENCE

Insignificant

mortals, who are as leaves are, and now flourish and grow warm with life, and feed on what the ground gives, but then fade away and are dead.

HOMER, The Iliad²³

* Humans are newly evolved. Our availability on a global scale as hosts for parasites is very recent. In the absence of medical countermeasures, we might expect, sometime in the future, the evolution of new kinds of microorganisms that pull our strings more artfully than any rabies virus could ever do.* It’s not hard to see how the components of this “fight-or-flight” response are all adaptive—evolved to get you through the crisis. That feeling of cold and emptiness at the pit of your stomach, for example, results from a reallocation of blood from digestion to the muscles.* True, of course, only for sexual organisms. Asexual beings, reproducing by splitting in two, cannot enhance the fitness of their descendants through a spirit of self-sacrifice.* Humans do this routinely. Large multi-ethnic states are revealingly called “fatherland” or “motherland.” Leaders encourage patriotic fervor—the word “patriotic” comes from the Greek for father. Especially in monarchies, it was easy to pretend that the nation was a family. The distant and powerful king was like many fathers. Everyone understood the metaphor.

Chapter 7

WHEN FIRE WAS NEW

Not I, but the world says it:

All is one.

HERACLITUS¹

The oxygen in the air is generated by green plants. They vent it into the atmosphere and we animals greedily breathe it in. So do many microbes and the plants themselves. We, in turn, exhale carbon dioxide into the atmosphere, which the green plants eagerly inhale. In a profound but largely unremarked intimacy, the plants and animals live off each other’s bodily wastes. The atmosphere of the Earth connects these processes, and establishes the great symbiosis between plants and animals. There are many other cycles that bind organism to organism and that are mediated by the air—cycles in nitrogen, for example, or sulfur. The atmosphere brings beings all over the world into contact; it establishes another kind of biological unity to the planet.

The Earth started out with an atmosphere essentially free of the oxygen molecule. As bacteria and other one-celled organisms arose, 3.5 billion years ago or earlier, some harvested sunlight, breaking water molecules apart in the first stage of photosynthesis. The oxygen, a waste gas, was simply released into the air—like emptying a sewer into the ocean. Resolutely independent, liberated from reliance on nonbiological sources of organic matter, the photosynthetic organisms proliferated. By the time there got to be enormous numbers of them, the air was full of oxygen.

Now oxygen is a peculiar molecule. We breathe it, depend on it, die without it, and so naturally have a good opinion of it. In respiratory distress, we want more oxygen, purer oxygen. As modern words (“inspire,” literally, breathe in; “aspire,” breathe toward; “conspire,” breathe with; “perspire,” breathe through; “transpire,” breathe across; “respire,” breathe again; and “expire,” breathe out) and Latin proverbs (such as Dum Spiro, spero, while I breathe, I hope) remind us, we associate many aspects of our nature with breathing. The word “spirit” —in all its incarnations (“spiritual,” “spirited,” alcoholic “spirits,” “spirits” of ammonia, and so forth)—also derives from the same Latin word for breath. Our fixation with breathing comes ultimately from considerations of energy efficiency: The oxygen we respire makes us about ten times more efficient in extracting energy from food than, say, yeast are; they know only how to ferment—breaking sugar down to some intermediate product such as ethyl alcohol rather than all the way back to carbon dioxide and water.*

But as a blazing log or a burning coal reminds us, oxygen is dangerous. Given a little encouragement, it can vandalize the intricate, painstakingly evolved structure of organic matter, leaving little more than some ash and a puff of vapor. In an oxygen atmosphere, even if you don’t apply heat, oxidation, as it’s called, slowly corrodes and disintegrates organic matter. Even much sturdier materials such as copper or iron tarnish and rust away in oxygen. Oxygen is a poison for organic molecules and doubtless was poisonous to the beings of the ancient Earth. Its introduction into the atmosphere triggered a major crisis in the history of life, the oxygen holocaust. The idea of organisms that gasp and choke to death after being exposed to a whiff of oxygen seems counterintuitive and bizarre, like the Wicked Witch of the West in The Wizard of Oz melting away to nothing when a little water falls on her. It’s the ultimate version of the adage “One man’s meat is another man’s poison.”†

Either you adapted to the oxygen, or you hid from it, or you died. Many died. Some reconciled themselves to live underground, or in marine muds, or in other environments where the deadly oxygen could not reach. Today all of the most primitive organisms—that is, the ones least related by genetic sequence to the rest of us—are microscopic and anaerobic; they prefer to live, or are forced to live, where the oxygen isn’t. Most organisms on Earth these days deal well with oxygen. They have elaborate mechanisms to repair the chemical damage done by oxygen, as—gingerly, held at molecular arm’s length it is used to oxidize food, extract energy, and drive the organism at high efficiency.

Human cells, and many others, deal with oxygen through a special, largely self-contained molecular factory called a mitochondrion, which is in charge of dealing with this poison gas. The energy extracted by oxidizing food is stored in special molecules and safely shipped to workstations throughout the cell. Mitochondria have their own kind of DNA—circles, or daisy chains, of As, Cs, Gs, and Ts, rather than double helices, instructions different at a glance from those that run the cell proper. But they’re enough like the DNA of the chloroplasts to make it clear that mitochondria also were once free-living bacteria-like organisms. The central role of cooperation and symbiosis in the early evolution of life is again evident.

Luckily for us, biochemical solutions were found to the oxygen crisis. If not, perhaps the only life on Earth today other than photosynthetic plants would be slithering in ooze and sucking at thermal vents in the abyssal depths. We have risen to the challenge and surmounted it—but only at enormous cost in the deaths of our ancestors and collateral relatives. These events show that there is no inherent foresight or wisdom in life that prevents it from making, in the short term at least, catastrophic mistakes. They also demonstrate that, long before civilization, life was producing toxic wastes on a massive scale, and for that miscalculation paying stiff penalties.

Through some such biochemical oversight, had things gone a little differently, perhaps all life on Earth would have been extinguished. Or perhaps some devastating asteroidal or cometary impact would have killed off all those tentative, fumbling microbes. Then, as we’ve said, organic molecules—both those synthesized on Earth and those falling from the skies—might have led to a new origin of life and an alternative evolutionary future. But the day comes when the gases leaking out of volcanos and fumaroles are no longer hydrogen-rich, no longer easy to make organic molecules from. Part of the reason is the oxygen atmosphere itself, which oxidizes these gases. Also, there gets to be a time when extraterrestrial organic molecules arrive so infrequently that they are an insufficient source of the stuff of life. Both these conditions seem to have been satisfied by around 2 or 3 billion years ago. Thereafter, if every living thing were to be wiped out, no new life could arise. The Earth would remain a desolate wasteland of a world into the remote future—until the Sun dies.

——

Back then, around 2 billion years ago or a little before, the oxygen in the Earth’s atmosphere—steadily increasing, to be sure, over preceding ages of geological time—began quickly to approach its present abundance. (In today’s air, one in every five molecules is O₂)

The first eukaryotic cell evolved a little earlier. Our cells are eukaryotes, which in Greek means, roughly, “good nuclei,” or “true nuclei.” As usual, we chauvinistic humans admire it because we have it. But they’ve been very successful. Bacteria and viruses are not eukaryotes, but flowers, trees, worms, fish, ants, dogs, and people are; all the algae, fungi, and protozoa, all the animals, all the vertebrates, all the mammals, all the primates. One of the key distinctions of the eukaryotic cell is that the governing machinery, the DNA, is encapsulated and set apart in a cell nucleus. As in a medieval castle, two sets of walls protect it from the outside world. Special proteins bond and contort the DNA, enveloping and embracing it, so a double helix that uncoiled would be about a meter long is compressed into a submicroscopic chamber at the heart of the cell. Perhaps the nucleus evolved—in the oxygen-rich vicinities of photosynthetic organisms—in part to protect DNA from oxygen while the mitochondria were busily exploiting it.

Each long DNA double helix is called a chromosome. Humans have 23 pairs of chromosomes. The total number of As, Cs, Gs, and Ts is about 4 billion pairs of letters in our double-stranded hereditary instructions. The information content is roughly that of a thousand different books with the size and fineness of print of the one you’re reading at this moment. While the variation from species to species is large, similar numbers apply to many other “higher” organisms.

Those same proteins that surround the DNA (themselves manufactured, of course, on instructions from the DNA) are responsible for switching genes on and off, in part by uncovering and covering the DNA. At appointed times, the exposed ACGT information of the DNA makes copies of certain sequences and dispatches them as messages out of the nucleus into the rest of the cell; in response to the commands in these telegrams, new molecular machine tools, the enzymes, are manufactured. They in turn control all the metabolism of the cell and all its interactions with the outside world. As with the children’s game called “Telephone” in America and “Grandmother’s Whispers” in Britain—in which a message is whispered successively by each player into the ear of the next—the longer the sequence of relays, the more likely it is that the communication will be garbled.

It’s a little like a kingdom with the distant DNA, isolated and guarded in the nucleus, as the monarch. The chloroplasts and mitochondria play the role of proudly independent dukedoms whose continuing cooperation is essential to the well-being of the realm.* Everybody else, every other molecule or complex of molecules working for the cell, has as its sole obligation punctilious obedience to orders. Great care must be taken that no message is mislaid or misunderstood. Occasionally, decisions are delegated to other molecules by the DNA, but generally every machine in the cellular toolshop is on a short tether.

However, even to the rank-and-file molecular workers in the cell, the monarch often seems half-witted and his decrees garbled and meaningless. As we’ve mentioned, most DNA of humans and other eukaryotes is genetic nonsense which the START and STOP instructions—like prudent assistants to a mad president—duly ignore. Immense reams of nonsense are in effect thoughtfully preceded by the notice “DRIVEL AHEAD. PLEASE IGNORE,” and followed by the message “END OF DRIVEL.” Sometimes the DNA goes into a stuttering frenzy in which the same ravings are repeated over and over. In the kangaroo rat of the American Southwest, for example, the sequence AAG is repeated 2.4 billion times, one after the other; TTAGGG, 2.2 billion times; and ACACAGCGGG, 1.2 billion times. Fully half of all the genetic instructions in the kangaroo rat are these three stutters.⁴ Whether repetition plays another role—maybe some internecine struggle for control by different gene complexes inside the DNA—is unknown. But superposed on precision replication and repair, and the meticulous preservation of DNA sequences from ages past, there is an element in the life of the eukaryotic cell that seems a little like farce.⁵

Some 2 billion years ago, several different hereditary lines of bacteria seem to have begun stuttering—making full copies of parts of their hereditary instructions over and over again; this redundant information then gradually specialized, and, excruciatingly slowly, nonsense evolved into sense.⁶ Similar repetitions arose early in the eukaryotes. Over long periods of time, these redundant, repetitive sequences undergo their own mutations, and sooner or later there will be, by chance, rare short passages among them that begin to make sense, that are useful and adaptive. The process is much easier than the classic imaginary experiment of the monkeys poking at typewriter keys long enough that eventually the complete works of William Shakespeare emerge. Here, even the introduction of a very short new sequence—representing only a punctuation mark, say—may be able to increase the survival chances of the organism in a changing environment. And here, unlike the monkeys at their typewriters, the sieve of natural selection is working. Those sequences that are slightly more adaptive (to continue the metaphor, we might say those sequences that correspond even slightly to Shakespearean prose—“TO BE OR,” immersed in gibberish, would be a start) are preferentially replicated. Out of randomly changing nonsense, the accidental bits of sense are preserved and copied in large numbers. Eventually, a great deal of sense emerges. The secret is remembering what works. Just such a drawing forth of meaning from random sequences of nucleotides must have happened in the very earliest nucleic acids, around the time of the origin of life.

An illuminating computer experiment analogous to the evolution of a short DNA sequence was performed by the biologist Richard Dawkins. He starts with a random sequence of twenty-eight English-language letters (spaces are counted as letters):

WDLTMNLT DTJBKWIRZREZLMQCO P.

His computer then repeatedly copies this wholly nonsensical message. However, at each iteration there is a certain probability of a mutation, of a random change in one of the letters. Selection is also simulated, because the computer is programmed to retain any mutations that move the sequence of letters even slightly toward a pre-selected goal, a particular, quite different sequence of twenty-eight letters. (Of course natural selection does not have some final ACGT sequence in mind, but—in preferentially replicating sequences that improve, even by a little, the fitness of the organism—it comes down to the same thing.) Dawkins’s arbitrarily chosen twenty-eight-letter sequence, toward which his selection was aiming, was

METHINKS IT IS LIKE A WEASEL.

(Hamlet, feigning madness, is teasing Polonius.)

In the first generation, one mutation in the random sequence occurs, changing the “K” (in DTJBKW …) to an “S.” Not much help yet. By the tenth generation, it reads

MDLDMNLS ITJISWHRZREZ MECS P,

and by the twentieth,

MELDINLS IT ISWPRKE Z WECSEL.

After thirty generations, we are at

METHINGS IT ISWLIKE B WECSEL,

and by forty-one generations, we’re there.

“There is a big difference,” Dawkins concludes, “between cumulative selection (in which each improvement, however slight, is used as a basis for future building), and single-step selection (in which each new ‘try’ is a fresh one). If evolutionary progress had had to rely on single-step selection, it would never have got anywhere.”⁷

Randomly varying the letters is an inefficient way to write a book, you might be thinking. But not if there are an enormous number of copies, each changing slightly generation upon generation, the new instructions constantly tested against the demands of the outside world. If human beings were devising the volumes of instruction contained in the DNA of the given species, we would, we might offhand imagine, just sit down and write the thing out, front to back, and tell the species what to do. But in practice we are wholly unable to do this, as is DNA. We stress again, the DNA hasn’t the foggiest notion a priori about which sequences are adaptive and which are not. The evolutionary process is not omnicompetent, far-seeing, crisis-avoiding, top-down. It is instead trial-and-error, short-term, crisis-mitigating, bottom-up. No DNA molecule is wise enough to know what the consequences will be if one segment of a message is changed into another. The only way to be sure is to try it out, keep what works, and run with it.

The more you know how to do, the more advanced you are—and, you might think, the better your chances for survival. But the DNA instructions for making a human being comprise some 4 billion nucleotide pairs, while those for a common one-celled amoeba contain 300 billion nucleotide pairs. There is little evidence that amoebae are almost a hundred times more “advanced” than humans, although the proponents of only one side of this question have been heard from to date. Again, some, maybe even most, of the genetic instructions must be redundancies, stutters, untranscribable nonsense. Again we glimpse deep imperfections at the heart of life.

Sometimes another organism inconspicuously slips through the defenses of the eukaryotic cell and steals into the heavily guarded inner sanctum, the nucleus. It attaches itself to the monarch, perhaps to the end of a time-tested and highly reliable DNA sequence. Now messages of a very different sort are dispatched out of the nucleus, messages that order the manufacture of a different nucleic acid, that of the infiltrator. The cell has been subverted.

Besides mutation, there are other ways (including infection and sex, to which we turn shortly) whereby new hereditary sequences arise. The net result is that a huge number of natural experiments are performed in every generation to test the laws, doctrine, and dogma encoded in the DNA. Each eukaryotic cell is such an experiment. Competition among DNA sequences is fierce; those whose commands work even slightly better become fashionable, and everyone has to have one.

The earliest known eukaryotic plankton floating on the surface of the oceans date to about 1.8 billion years ago; the earliest eukaryotes with a sex life to 1.1 billion years ago; the great burst of eukaryote evolution (that would lead to algae, fungi, land plants and animals, among others) to about the same epoch; the earliest protozoa to about 850 million years ago; and the origin of the major animal groups and the colonization of the land to about 550 million years ago.⁸ Many of these epochal events may be tied to the increasing atmospheric oxygen. Since the oxygen is generated by plants, we see life forcing its own evolution on a massive scale. Of course, we can’t be sure of the dates; next week paleontologists may discover examples still more ancient. The sophistication of life has increased greatly over the last 2 billion years, and the eukaryotes have done extremely well—as we have only to look around us to verify.

But the eukaryotic kind of life, very different from the rough-and-ready first organisms, is exquisitely dependent on the near-perfect functioning of an elaborate molecular bureaucracy, whose responsibilities include covering up the fits of incompetence in the DNA. Some DNA sequences are too fundamental to the central processes of life to be able safely to change. Those key instructions simply stay fixed, precisely replicated, generation after generation, for aeons. Any significant alteration is simply too costly in the short term, whatever its ostensible virtues may be in the long, and the carriers of such change are wiped out by selection. The DNA of eukaryotic cells reveals segments that clearly and specifically come from the bacteria and archaebacteria of long ago. The DNA inside us is a chimera, long ACGT sequences having been adopted wholesale from quite different and extremely ancient beings, and faithfully copied for billions of years. Some of us—much of us—is old

——

Eventually, there got to be many beings whose cells had specialized functions, just as, for example, the chloroplasts or mitochondria within a given cell have specialized functions. Some cells were in charge of, say, disabling and removing poisons; others were the conduits of electrical impulses, part of a slowly evolving neural apparatus in charge of locomotion, breathing, feelings, and—much later—thoughts. Cells with quite diverse functions interacted harmoniously. Still larger beings evolved separate internal organ systems, and again survival depended on the cooperation of very different constituent parts. Your brain, heart, liver, kidneys, pituitary, and sexual organs generally work together well. They are not in competition. They make a whole that is much more than the sum of the parts.

Our ancestors and collateral relatives were restricted to the seas until about 500 million years ago, when the first amphibian crawled out onto the land. A significant ozone layer may not have developed until about then. These two facts are probably related. Earlier, deadly ultraviolet light from the Sun reached the surface of the land, frying any intrepid pioneer attempting to homestead there. Ozone, as we’ve mentioned, is produced from the oxygen in the upper air by the Sun’s radiation. So that reckless oxygen pollution of the ancient atmosphere, generated by the green plants, seems to have had another accidental and this time salutary consequence: It made the land habitable. Who would have figured?

Hundreds of millions of years later, a rich biology filled almost every nook and cranny of the land. The moving continental plates now carried with them cargoes of plants and animals and microbes. When new continental crust appeared, it was quickly colonized by life. When old continental crust was carried down into the Earth’s interior, we might be worried that its living cargo would be carried down with it. But the conveyor belt of plate tectonics moves only an inch a year. Life is quicker. Ancient fossils, though, can’t jump off the conveyer belt. They are destroyed by plate tectonics. The precious records and remains of our ancestors are swept down into the semi-fluid mantle and cremated. We are left with the odd remnants that by accident escaped.

Before there was enough oxygen, or anything combustible, fire was impossible, an unrealized potential, latent in matter (just as the release of nuclear energy was unrealized during the tenure of humans on Earth until 1942–1945). There must, therefore, have been an age of the first flame, a time when fire was new. Perhaps it was a dead fern, ignited by a flash of lightning. Since plants colonized the land long before animals, there was no one to notice: Smoke rises; suddenly, a tongue of red flickers upward. Perhaps a little thicket of vegetation has caught fire. The flame isn’t a gas, or a liquid, or a solid. It’s some other, some fourth state of matter that physicists call plasma. Never before had Earth been touched by fire.

Long before humans made use of fire, plants did. When the population density is high and plants of different species are closely packed together, they fight—for access to nutrients and underground water, but especially for sunlight. Some plants have invented hardy, fire-resistant seeds, along with stems and leaves that readily burst into flames. Lightning strikes, an intense fire burns out of control, the seeds of the favored plant survive, and the competition—seeds and all—has been burned to a crisp. Many species of pines are the beneficiaries of this evolutionary strategy. Green plants make oxygen, oxygen permits fire, and fire is then used by some green plants to attack and kill their neighbors. There is hardly any aspect of the environment that has not been used, one way or another, in the struggle for existence.

A flame looks unearthly, but in this neck of the Cosmos it’s unique to Earth. Of all the planets, moons, asteroids, and comets in our Solar System, there is fire only on Earth—because there are large amounts of oxygen gas, O₂, only on Earth. Fire was, much later, to have profound consequences for life and intelligence. One thing leads to another.

——

The human pedigree wends its tortuous way back to the beginning of life 4 billion years ago. Every being on Earth is our relative, since we all come from that same point of origin. And yet, precisely because of evolution, no lifeform on Earth today is an ancestor of ours. Other beings did not stop evolving because a pathway that would someday lead to humans had just been generated. No one knew what branch in the evolutionary tree was going where, and no one before humans could even raise the question. The beings from whom our ancestral line deviated continued to evolve, inside and out, or became extinct. Almost all became extinct. We know from the fossil record something of who our predecessors were, but we cannot bring them into the laboratory for interrogation. They are no more.

Luckily, though, there are organisms alive today that are similar—in some cases, very similar—to our ancestors. The beings that left stromatolite fossils probably performed photosynthesis and in other respects behaved as contemporary stromatolitic bacteria do. We learn about them by examining their surviving close relatives. But we cannot be absolutely sure. For example, ancient organisms were not necessarily and in all respects simpler than modern ones. Viruses and parasites, in general, show signs of having evolved by loss of function from some more self-sufficient forebear.

Many features in the biological landscape arrived late. Sex, for example, doesn’t seem to have evolved until three quarters of the history of life till now had passed. Animals big enough for us to see—had we been there—animals made of many different kinds of cells, also do not seem to have emerged until almost three quarters of the way between the origin of life and our time. Except for microbes, there were no beings on the land until something like 90%, and no creatures with big brains for their body sizes until about 99% of the history of life thus far was over.

Enormpus gaps yawn through the fossil record, although less so now than in Darwin’s time. (If there were more paleontologists in the world, we’d doubtless be a little further along.) From the comparatively low rate of discovery of new fossils, we know that huge numbers of ancient organisms have not been preserved. There’s something poignant about all those species—some ancestral to humans, on some sturdy trunk of our family tree, most not—about whom we know nothing, not a single example of them having survived, even in fossil form, to our own time.

Even when the incompleteness of the fossil record is taken into account, the diversity or “taxonomic richness” of life on Earth is found to have been steadily increasing, especially in the last 100 million years.⁹ Diversity seems to have peaked just as humans were really getting going, and has since declined markedly—in part because of the recent ice ages, but in larger part because of the depredations of humans, both intentional and inadvertent. We are destroying the diversity of beings and habitats out of which we emerged. Something like a hundred species become extinct each day. Their last remnants die out. They leave no descendants. They are gone. Unique messages, painstakingly preserved and refined over eons, messages that a vast succession of beings gave up their lives to pass on to the distant future are lost forever.

More than a million species of animals are now known on Earth, and perhaps 400,000 species of eukaryotic plants. There are at least thousands of known species of other organisms, non-eukaryotes, including bacteria. Doubtless we have missed many, probably most. Some estimates of the number of species range beyond 10 million; if so, we have even glancing acquaintance with less than 10% of the species on Earth. Many are becoming extinct before we even know of their existence. Most of the billions of species of life that have ever lived are extinct. Extinction is the norm. Survival is the triumphant exception.

We’ve sketched the changes on the Earth’s surface at the end of the Permian Period, some 245 million years ago; they resulted in the most devastating biological catastrophe so far displayed in the fossil record. Perhaps as many as 95% of all the species then living on Earth became extinct.* Many kinds of filter-feeding animals attached to the ocean floor, beings that had for hundreds of millions of years characterized life on Earth, disappeared. Ninety-eight percent of the families of crinoids became extinct. We don’t hear much about crinoids these days; sea lilies are their surviving remnant. Wholesale extinctions also occurred among the amphibians and reptiles that had settled the land. On the other hand, sponges and bivalves (like clams) did comparatively well in the late Permian extinction—one consequence of which is that they are still plentiful on Earth today.

Following mass extinctions it typically takes 10 million years or more for the variety and abundance of life on Earth to recover—and then, of course, there are different organisms around, perhaps better adapted to the new environment, perhaps with better long-term prospects, or perhaps not. In the millions of years following the end of the Permian Period, volcanism subsided and the Earth warmed. This killed off many land plants and animals that had been adapted to the late Permian cold. Out of this set of cascading climatic consequences, conifers and ginkgoes emerged. The first mammals evolved from reptiles in the new ecologies established after the Permian extinctions.

Of all the species of animals alive at the end of the Permian, only about twenty-five of them, it is estimated, have left any descendants at all; ten of which account for 98% of the contemporary families of vertebrates, which comprise about forty thousand species.¹⁰ The rate of evolutionary change is full of fits and starts, blind alleys and sweeping change—the latter driven often by the first filling of a previously untenanted ecological niche. New species appear quickly and then persist for millions of years. In only the last 2% or 3% of the history of life on Earth, the extravagant diversification of the placental mammals has producedshrews, whales, rabbits and mice, anteaters, sloths, armadillos, horses, pigs and antelopes, elephants, sea cows, wolves, bears, tigers, seals, bats, monkeys, apes, and men¹¹

For the vast bulk of Earth history, until just recently, not one of these beings had existed. They were present only potentially.

Think of the genetic instructions of a given being, perhaps a billion ACGT nucleotide pairs long. Randomly change a few nucleotides. Perhaps these will be in structural or inactive sequences and the organism is in no way altered. But if you change a meaningful DNA sequence, you change the organism. Most such changes, as we keep saying, are maladaptive; except in rare instances, the bigger the change, the more maladaptive it is. For all of mutation, gene recombination, and natural selection put together, the continuing experiment of evolution on Earth has brought into being only a minute fraction of the range of possible organisms whose manufacturing instructions could be specified by the genetic code. The vast bulk of those beings, of course, would be not merely maladapted, not just freaks, but wholly inviable. They could not be born alive. Nevertheless, the total number of possible functioning, living beings is still vastly greater than the total number of beings who have ever been. Some of those unrealized possibilities must be, by any standard we wish to adopt, better adapted and more capable than any Earthling who has ever lived.

——

Sixty-five million years ago most of the species on Earth were snuffed out—probably because of a massive cometary or asteroidal collision. Among those killed off were all the dinosaurs, which had for nearly 200 million years—from before the breakup of Gondwanaland—been the dominant species, the ubiquitous masters of life on Earth. This extinction event removed the chief predators of a small, fearful, cowering nocturnal order of animals called the mammals. If not for that collision—a late step in the tidying up of interplanetary space of the remaining worlds on eccentric orbits—we humans and our primate ancestors would never have come to be. And yet, if that comet had been on a slightly different trajectory, it might have missed the Earth entirely. Perhaps, in its many relays around the Sun, its ices would all have melted and its rocky and organic contents slowly spewed as fine powder into interplanetary space. Then all it would have provided for life on Earth would have been a periodic shower of meteors, perhaps admired by some newly-evolved, curious, large-brained reptile.

On the scale of the Solar System, the extinction of the dinosaurs and the rise of the mammals seem to have been a very near thing. The causality corridor, figuratively speaking, was only inches wide. Had the comet been traveling a little slower or faster or headed in a slightly different direction, no collision would then have occurred. If other comets that in our real history missed the Earth had been on slightly different trajectories, they would have hit the Earth and killed off life in some different epoch. The cosmic collision roulette, the extinction lottery, reaches into our own time.

At the depth in the fossil record above which there are no more dinosaurs, there is, worldwide, a telltale thin layer of the element iridium, which is abundant in space but not on the Earth’s surface. There also are tiny grains bearing the signs of a collosal impact. This evidence tells us of a high-speed collision of a small world with the Earth which distributed fine particles worldwide. The remains of the impact crater may have been discovered in the Gulf of Mexico near the Yucatan Peninsula. But something else is found in this layer as well: soot. Planet-wide, the time of this great impact was also the time of a global fire. The debris from the impact explosion, spewed out into the high atmosphere and falling back through the air all over the Earth—a continuous meteor shower filling the sky—illuminated the ground far more brightly than the noonday Sun. Land plants everywhere on Earth burst into flames, all at once. Most of them were consumed. There is an odd causal nexus connecting oxygen, plants, giant impacts, and world-immolating fire.

There are many ways in which such an impact could have extinguished long-established and, if we may call them that, self-confident forms of life. After the initial burst of light and heat, a thick pall of impact dust enveloped the Earth for a year or more. Perhaps even more important than the world fire, the lowered temperatures, and a planet-wide acid rain was the absence for a year or two of enough light for photosynthesis. The primary photosynthesizing organisms in the oceans (then as now covering most of the Earth) are little one-celled plants called phytoplankton. They are especially vulnerable to lowered light levels because they lack major food reserves. Once the lights get turned out their chloroplasts can no longer generate carbohydrates from sunlight, and they die. But these little plants are the principal diet of one-celled animals that are eaten by larger, shrimp-like creatures, that are eaten by small fish, that are in turn eaten by large fish. Turn off the lights, wipe out the phytoplankton, and the entire food chain, this elaborate house of cards, collapses. Something similar is true on land.

The beings of Earth depend on one another. Life on Earth is an intricately woven tapestry or web. Yank out a few threads here and there, and you can’t be sure whether that’s all the damage you’ve done, or whether the whole fabric will now unravel.

Insects and other arthropods are the principal agents by which dead plants and animal excrement are cleaned up. Scarabs—the dung beetles identified with the sun god and worshipped by the ancient Egyptians—are specialists in waste management. They collect the nitrogen-rich animal excrement accumulating on the surface of our planet and transport this fertilizer down where the plant roots are. Some sixteen thousand beetles have been counted on a single fresh elephant pat in Africa; two hours later the pat was gone.¹² The Earth’s surface would be very different (and very messy) without dung beetles and their like. In addition, the microscopic feces of mites and springtails are major constituents of the soil humus from which the plants grow. Animals then eat the plants. We live off each other’s solid wastes as well.

Other inhabitants of the soil kill off the young plants. Here is Darwin’s account of a little experiment he did to illustrate the hidden ferocity lurking just beneath the placid surface of a country garden:[On] a piece of ground 3 feet long and 2 feet wide, dug and cleared, and where there could be no choking from other plants, I marked all the seedlings of our native weeds as they came up, and out of 357 no less than 295 were destroyed, chiefly by slugs and insects If turf which has long been mown, and the case would be the same with turf closely browsed by quadrupeds, be let to grow, the more vigorous plants gradually kill the less vigorous though fully grown plants . .¹³

Some plants provide food for specific animals, in turn, the animals act as agents for the sexual reproduction of the plants—in effect, couriers taking sperm from male plants and using it for artificial insemination of female plants. This is not quite artificial selection, because the animals are not much in charge. The currency these procurers are paid in is usually food. A bargain has been struck. Maybe the animal is a pollinating insect, or bird, or bat; or a mammal to whose furry coat the reproductive burrs adhere; or maybe the deal is food supplied by the plants in exchange for nitrogenous fertilizer supplied by the animals. Predators have symbionts that clean their coats or scales or pick their teeth in exchange for leavings. A bird eats a sweet fruit; the seeds pass through its digestive tract and are deposited on fertile ground some distance away: another business transaction consummated. Fruit trees and berry-bearing bushes often take care that their offerings to the animals are sweet only when the seeds are ready to be dispersed. Unripe fruit gives bellyaches, the plants’ way of training the animals.

The cooperation between plants and animals is uneasy. The animals cannot be trusted; given a chance, they’ll eat any plant in sight. So the plants protect themselves from unwelcome attention with thorns, or by producing irritants, or poisons, or chemicals that make the plant indigestible, or agents that interfere with the predator’s DNA. In this endless slow-motion war, the animals then produce substances that disable these adaptations by the plants. And so on.

The beasts and vegetables and microbes are the interlocking parts, the gear train, of a vast, intricate and very beautiful ecological machine of planetary proportions, a machine plugged into the Sun. Pretty nearly, all flesh is sunlight.

Where the ground is covered with plants perhaps 0.1% of the sunlight is converted into organic molecules. A plant-eating animal saunters by and eats one of these plants. Typically the herbivore extracts about a tenth of the energy in the plant, or about one ten-thousandth of the sunlight that could, with 100% efficiency, have been stored in the plant. If the herbivore is now attacked and eaten by a carnivore, about 10% of the available energy in the prey will wind up in the predator. Only one part in a hundred thousand of the original solar energy makes it to the carnivore. There are no perfectly efficient engines, of course, and we expect losses at each stage in the food chain. But the organisms at the top of the food chain seem inefficient to the point of irresponsibility.*

A vivid image of the interconnection and interdependence of life on Earth was provided by the biologist Clair Folsome, who asks you to imagine what you would see if all the cells of your body, flesh and bones, were magically removed:What would remain would be a ghostly image, the skin outlined by a shimmer of bacteria, fungi, round worms, pin worms and various other microbial inhabitants. The gut would appear as a densely packed tube of anaerobic and aerobic bacteria, yeasts, and other microorganisms. Could one look in more detail, viruses of hundreds of kinds would be apparent throughout all tissues.

And, Folsome stresses, any other plant or animal on Earth, under the same dispensation, would reveal a similar “seething zoo of microbes.” ¹⁴

——

A biologist from some other solar system, in an unblinking examination of the teeming lifeforms of Earth, would surely note that they are all made of almost exactly the same organic stuff, the same molecules almost always performing the same functions, with the same genetic codebook in use by almost everybody. The organisms on this planet are not only kin; they live in intimate mutual contact, imbibing each other’s wastes, dependent on one another for life itself, and sharing the same fragile surface layer. This conclusion is not ideology, but reality. It depends not on authority, faith, or special pleading by its proponents, but on repeatable observation and experiment.

The beings of our planet are imperfectly linked and coordinated; and there is certainly nothing like a collective intelligence of all the life on Earth—in the sense that all the cells of a human body are subject, within stringent constraints, to a supervening volition. Still, the alien biologist might be excused for lumping together the whole biosphere—all the retroviruses, mantas, foraminifera, mongongo trees, tetanus bacilli, hydras, diatoms, stromatolite-builders, sea slugs, flatworms, gazelles, lichens, corals, spirochetes, banyans, cave ticks, least bitterns, caracaras, tufted puffins, ragweed pollen, wolf spiders, horseshoe crabs, black mambas, monarch butterflies, whiptail lizards, trypanosomes, birds of paradise, electric eels, wild parsnips, arctic terns, fireflies, titis, chrysanthemums, hammerhead sharks, rotifers, wallabies, malarial plasmodia, tapirs, aphids, water moccasins, morning glories, whooping cranes, komodo dragons, periwinkles, millipede larvae, angler fish, jellyfish, lungfish, yeast, giant redwoods, tardigrades, archaebacteria, sea lilies, lilies of the valley, humans, bonobos, squid and humpback whales—as, simply, Earthlife. The arcane distinctions among these swarming variations on a common theme may be left to specialists or graduate students. The pretensions and conceits of this or that species can readily be ignored. There are, after all, so many worlds about which an extraterrestrial biologist must know. It will be enough if a few salient and generic characteristics of life on yet another obscure planet are noted for the cavernous recesses of the galactic archives.

* Seawater itself is opaque to ultraviolet light beyond a certain depth, and the early oceans were very likely covered by a slick of ultraviolet-absorbing organic molecules. The seas were safe.* A biochemical imperfection exploited by the beer, wine, and liquor industries, which profitably manufacture this addictive and dangerous drug, C₂H₅OH (where C stands for a carbon atom, O for oxygen, and H for hydrogen). Millions of people worldwide die from imbibing it each year. Or, looked at another way, distillers have been exploited by the fermenting bacteria and yeast, who have gotten us to arrange for their growth and reproduction on a worldwide, industrial scale—because we love to drink ourselves senseless on microbial wastes. If they could speak, perhaps they would boast about how cleverly they’ve domesticated the humans. Yeasts also colonize dark, moist, oxygen-poor parts of the human body, another way in which we serve them.† Another example was given by the ancient Greek philosopher Heraclitus: “The sea,” he said, “is most pure and most polluted water: for fish, drinkable and life-preserving; for men, undrinkable and death-dealing.”²* The genetic code of the mitochondrion is just a little different from that of the nucleus—as if it had evolved so that the nuclear DNA could not tell the mitochondria what to do, a token of independence. For example, AGA means STOP for mitochondrial nucleic acids, whereas for the nucleic acids that hail from the nucleus of a cell, it codes for a particular amino acid, arginine.³ The mitochondria simply ignore instructions from the capital, which to them are mainly gibberish with occasional lucid passages; they follow the commands of their own feudal leader, the mitochondrial DNA.* Ninety-five percent seems awfully close to 100%, and it’s disquieting to be reminded that the great rumbling, internal tectonic engine can inadvertently kill off so many of us up here because of some hiccups down there.* In principle the ecological machine could continue as long as the Sun continues to shine, estimated at another 5 billion years. It’s hard not to wonder—we carnivores at the apex of the food chain, the beneficiaries of a process with a thousandth of a percent efficiency—if there might not be some more efficient way for us to harness the Sun.

Chapter 8

SEX AND DEATH

[S]ex endows the individual with a dumb and

powerful instinct, which carries his body and

soul continually towards another; makes it one

of the dearest employments of his life to select

and pursue a companion, and joins to

possession the keenest pleasure, to rivalry the

fiercest rage, and to solitude an eternal

melancholy. What more could be needed to

suffuse the world with the deepest meaning

and beauty?

GEORGE SANTAYANA,

The Sense of Beauty (1896)¹

Death is the great reprimand which the will to

live, or more especially the egoism which is

essential to this, receives through the course of

nature; and it may be conceived of as a

punishment for our existence. It is the painful

loosening of the knot which the act of

generation had tied …

ARTHUR SCHOPENHAUER,

The World as Will and Idea, Supplements²

Fireflies out on a warm summer’s night, seeing the urgent, flashing, yellow-white phosphorescence below them, go crazy with desire; moths cast to the winds an enchantment potion that draws the opposite sex, wings beating hurriedly, from kilometers away; peacocks display a devastating corona of blue and green and the peahens are all aflutter; competing pollen grains extrude tiny tubes that race each other down the flower’s female orifice to the waiting egg below; luminescent squid present rhapsodic light shows, altering the pattern, brightness, and color radiated from their heads, tentacles, and eyeballs; a tapeworm diligently lays a hundred thousand fertilized eggs in a single day; a great whale rumbles through the ocean depths uttering plaintive cries that are understood hundreds or thousands of kilometers away, where another lonely behemoth is attentively listening; bacteria sidle up to one another and merge; cicadas chorus in a collective serenade of love; honeybee couples soar on matrimonial flights from which only one partner returns; male fish spray their spunk over a slimy clutch of eggs laid by God-knows-who; dogs, out cruising, sniff each other’s nether parts, seeking erotic stimuli; flowers exude sultry perfumes and decorate their petals with garish ultraviolet advertisements for passing insects, birds, and bats; and men and women sing, dance, dress, adorn, paint, posture, self-mutilate, demand, coerce, dissemble, plead, succumb, and risk their lives. To say that love makes the world go around is to go too far. The Earth spins because it did so as it was formed and there has been nothing to stop it since But the nearly maniacal devotion to sex and love by most of the plants, animals, and microbes with which we are familiar is a pervasive and striking aspect of life on Earth. It cries out for explanation.

What is all this in aid of? What is this torrent of passion and obsession about? Why will organisms go without sleep, without food, gladly put themselves in mortal danger for sex? Some beings, among them good-sized plants and animals such as dandelions, salamanders, some lizards and fish, can reproduce without sex. For more than half the history of life on Earth organisms seem to have done perfectly well without it. What good is sex?

What’s more, sex is expensive. It takes formidable genetic programming to wire in seductive songs and dances; to manufacture sexual pheromones; to grow heroic antlers used only in defeating rivals; to establish interlocking parts, rhythmic motions, and mutual zest for sex. All this represents a drain on energy resources that could just as well be used for something of more obvious short-term benefit to the organism. Also, some of what the beings of Earth do or endure for sex endangers them directly: The displaying peacock is much more vulnerable to predators than if he were inconspicuous, fearful, and dun-colored. Sex provides a convenient and potentially deadly channel for the transmission of disease. All these costs must be more than offset by the benefits of sex. What are those benefits?

——

Embarrassingly, biologists don’t fully understand what sex is for. In this respect the situation has hardly changed since 1862 when Darwin wroteWe do not even in the least know the final cause of sexuality; why new beings should be produced by the union of the two sexual elements … The whole subject is as yet hidden in darkness.

Through 4 billion years of natural selection, instructions have been honed and fine-tuned—more elaborate, more redundant, more foolproof, more multiply capable instructions—sequences of As, Cs, Gs, and Ts, manuals written out in the alphabet of life in competition with other similar manuals published by other firms. The organisms become the means through which the instructions flow and copy themselves, by which new instructions are tried out, on which selection operates. “The hen,” said Samuel Butler, “is the egg’s way of making another egg.” It is on this level that we must understand what sex is for.

We do understand much of the molecular machinery of sex. To begin with, let’s consider some of those microbial beings that routinely do what many people would consider impossible—reproducing without sex*: Once every generation their nucleic acids faithfully copy themselves out of the A, C, G, and T molecular building blocks they manufacture for the purpose. The two functionally identical DNAs then each take half the cell and run—a little like a property settlement in a divorce. Sometime later, the process repeats itself. Each generation is a dreary repetition of the one before, and every organism is the spitting image—nearly identical, down to the last mitochondrion and flagellar propulsion system—of its single parent. If the organism is well-adapted and the environment repetitive and static, this arrangement might work well. The monotony is broken, rarely, by mutation. But mutation, as we’ve stressed, is random and much more likely to do harm than good. All subsequent generations will be afflicted unless, improbably, there’s a compensating mutation down the line. The pace of evolution under such circumstances must be slow, as indeed seems to be reflected in the fossil record between 3.5 and about 1 billion years ago—until the invention of sex.

Now, instead of slow, random change in the genetic materials, imagine that you could in one step glue onto part of the existing messages a long, complex set of new instructions—not merely a change in one letter of one word of the DNA, but whole volumes of consumer-tested manuals. Imagine the same kind of reshuffling occurring in subsequent generations. This is a dumb idea if you’re ideally adapted to an unchanging or very marginal environment; then any change is for the worse. But if the world you must adapt to is heterogeneous and dynamic, evolutionary progress is better served when reams of new genetic instructions are made available in each generation than when all there is to deal with is an occasional conversion of an A into a C. Also, if you can reshuffle genes, you or your descendants can get out of the trap set by the accumulation, generation after generation, of deleterious mutations.³ Harmful genes can quickly be replaced by advantageous ones. Sex and natural selection work as a kind of proofreader, replacing the inevitable mutational errors by uncontaminated instructions. This may be why the eukaryotes diversified—into the separate evolutionary lines that would lead to protozoa (like paramecia), plasmodia (like those that cause malaria), algae, fungi, all land plants and all animals—just around the time that eukaryotes hit upon sex.

Some modern organisms—ranging from bacteria to aphids to aspens—sometimes reproduce sexually and sometimes asexually. They can go either way. Others—dandelions, for example, and certain whiptail lizards—have recently evolved from sexual to asexual forms, as seems clear from their anatomy and behavior: Dandelions produce flowers and nectar that are useless for their current reproductive style; no matter how busy the bees are, they cannot be agents for dandelion fertilization. In the whiptail lizards, everyone is female and the hatchlings have no biological fathers. But reproduction still requires heterosexual foreplay—the formality of copulation with males of other, still sexual, lizard species, even though they cannot impregnate these females, or a ritual pseudocopulation with other females of the same species.⁴ Apparently, we are observing these dandelions and lizards so soon after their evolution from sexual to asexual beings that there has been insufficient time for the scripts and props of sex to have withered away. Perhaps there are circumstances when it’s wise to reproduce sexually and others when it isn’t; certain beings may prudently cycle from one state to the other, depending on the external environment. This option is, however, unavailable to us. We are stuck with sex.

Today a reshuffling of genetic instructions, similar to what happens in sex, occurs—oddly—in infection: A microbe enters a larger organism, evades its defenses, and insinuates its nucleic acid onto that of its host. There’s an intricate machinery in the cell, idling and ready to go, which reads and replicates preexisting sequences of A, C, G, and T. The machinery’s not good enough, though, to distinguish foreign nucleic acids from native ones. It’s a printing press for instruction manuals, and it will copy anything when its buttons are pushed. The parasite pushes the buttons, the cell’s enzymes are issued new instructions, and hordes of newly minted parasites are spewed out, itching for more subversion.

Occasionally, the dead manage to have sex and generate offspring. When a bacterium dies, its contents are spilled into the surroundings. Its nucleic acids don’t know much about the death of the bacterium and even as they slowly fall to pieces, the fragments remain for a time functional—like the severed leg of an insect. Should such a fragment be ingested by a passing (and intact) bacterium, it may be incorporated into the resident nucleic acids. Perhaps it is used as an independent record of what undamaged instructions should say, helpful in repairing DNA altered by oxygen. Maybe this extremely rudimentary form of sex arose along with the Earth’s oxygen atmosphere.

Bizarre chimerical gene combinations happen more rarely—for example, between bacteria and fish (not only are there bacterial genes in fish today; there are also fish genes in bacteria), or baboons and cats. They seem to have been brought about by a virus attaching itself to the DNA of a host organism, reproducing with and accommodating to the host over the generations, and then shaking loose to infect another species while carrying some of the original host’s genes with it. Cats are known to have acquired a baboon virogene somewhere on the shores of the Mediterranean Sea 5 to 10 million years ago.⁵ Viruses are looking more and more as if they are peripatetic genes that cause disease only incidentally. But if genetic exchanges can occur today in such widely divergent organisms, it must be far easier for them to occur, by accident, in organisms of the same or very closely related species. Perhaps sex started out as an infection, becoming later institutionalized by the infecting and infected cells.

Two distant relatives, members of the same species, each in the process of replication, find their nucleic acid strands, one from each, laid down, cozily, alongside one another. A short segment of one very long sequence might be, say,

… ATG AAG TCG ATC CTA …

and the corresponding segment of the other

… TAC TTC GGG CGG AAT …

The long nucleic acid molecules both break apart at the same place in the sequence (here, just after AAG in the first molecule and TTC in the second), whereupon they recombine, each picking up a segment of the other:

… ATG AAG GGG CGG AAT …

and

… TAC TTC TCG ATC CTA …

Because of this genetic recombination, there are two new sequences of instructions and therefore two new organisms in the world—not exactly chimeras, since they come from the same species, but nevertheless each constituting a set of instructions that may never before have coexisted in the same being.

A gene, as we’ve said, is a sequence of perhaps thousands of As, Cs, Gs, and Ts which codes for a particular function, usually by synthesizing a particular enzyme. When DNA molecules are severed, just prior to recombination, the cut occurs at the beginning or the end of a gene, and almost never in its middle. One gene may have many functions. Important characteristics of the organism—height, say, aggressiveness, coat color, or intelligence—will generally be the consequence of many different genes acting in concert.

Because of sex, different combinations of genes can now be tried out, to compete with the more conventional varieties. A promising set of natural experiments is being performed. Instead of generations patiently waiting in line for a lucky sequence of mutations to occur—it might take a million generations for the right one, and the species might not be able to wait that long—the organism can now acquire new traits, new characteristics, new adaptations wholesale. Two or more mutations that don’t do much good by themselves, but that confer an enormous benefit when working in tandem, might be acquired from widely separated hereditary lines. The advantages (for the species, at least) seem clear, if only the costs were bearable. Genetic recombination provides a treasure trove of variability on which natural selection can act.⁶

Another proposed explanation for the persistence of sex, wonderful in its novelty, invites us to consider the age-old arms race between parasitic microbes and their hosts. There are more disease microorganisms in your body at this moment than there are people on Earth. A single bacterium reproducing twice an hour will leave a million successive generations during your lifetime. With so many microbes and so many generations, an immense number of microbial varieties are available for selection to operate on—especially selection to overcome your body’s defenses. Some microbes change the chemistry and form of their surfaces faster than the body can generate new model antibodies; these tiny beings routinely outwit at least some parts of the human immune system. For example, an alarming 2% of the plasmodium parasites that cause malaria significantly change their shapes and styles of stickiness each generation.⁷ In light of the formidable adaptive powers of disease microorganisms, a real danger would arise if we humans were genetically identical, generation after generation. Very quickly, the blur of evolving pathogens might have our number. A variety that outsmarts our defenses might click into place. But if our DNA is reassorted every generation, we have a much better chance of keeping ahead of the potentially deadly infestation of disease microbes.⁸ In this highly regarded hypothesis, sex provides essential confusion to our enemies and is the key to health.

——

Because females and males are physiologically different, they sometimes pursue different strategies, each to propagate its own hereditary line; and these strategies, while of course not wholly incompatible, introduce a certain element of conflict in the relations between the sexes. In many species of reptiles, birds, and mammals, the female produces only a small number of eggs at a time, perhaps only once a year. It then makes evolutionary sense for her to be discriminating in her choice of mates, and devoted to nurturing the fertilized eggs and the young.

The male, on the other hand, with plentiful sperm cells—up to hundreds of millions per ejaculation and the capability of many ejaculations a day in a healthy young primate—can often better continue his hereditary line through numerous and indiscriminate matings, if he can pull it off. He may be much more ardent and eager, and at the same time much more likely to drift from partner to partner—cajoling, displaying, intimidating, and impregnating as many females as possible. Moreover, since there are other males with identical strategies, a male can’t be sure that a particular fertilized egg or hatchling or cub is his; why should he spend time and effort nurturing and raising a youngster that might not even carry his genes? The investment might benefit his rival’s descendants and not his own. Better to be off fertilizing more females.

This is by no means an invariable pattern, though; there are species in which the female is eager to mate with many males, and there are species in which the male plays a major, even a primary, role in raising the young. Over 90% of the known species of birds are “monogamous”; so are 12% of the monkeys and apes, to say nothing of all the wolves, jackals, coyotes, foxes, elephants, shrews, beavers, and miniature antelope.⁹ However, monogamous doesn’t mean sexually exclusive; in many species in which the male helps raise the children and provides care for their mother, he also is sneaking out for a little sex on the side; and she is often receptive to other males. Biologists call it a “mixed mating strategy,” or “extra-pair copulation.” As much as 40% of the young reared by “monogamous” bird pairs are revealed by DNA fingerprinting to have been sired by extramural encounters, and numbers almost as large may apply to humans. Still, the motif of nurturing females, who are choosy about their sex partners, and males given to sexual adventure and many partners is very widespread, especially among the mammals.

——

There’s a good deal of plumbing, odor signaling, and other machinery in higher organisms to get the genes of one organism in contact with those of another, so the molecules can lie down next to one another and recombine. But that’s mere hardware. The central sexual event, from bacteria to humans, is the exchange of DNA sequences. The hardware serves the purpose of the software.

In its beginning, all sex must have been fumbling, confused, haphazard, the microbial equivalent of bedroom farce. But the advantages that sex confers on future generations seem to be so great that, provided the costs were not too high, selection for improved sexual hardware must soon have been up and running, along with whatever new software was required to stiffen a resolve for sexual congress. Passionate organisms, other things being equal, leave more descendants than those of more tepid dispositions. Unenlightened on the selective advantage of new DNA combinations, organisms nevertheless developed an overwhelming compulsion to trade their hereditary instructions. Like hobbyists who exchange comic books, postage stamps, baseball cards, enameled pins, foreign coins, or celebrity autographs, they didn’t think it out; they just couldn’t help themselves. Trade is at least a billion years old.

Two paramecia may conjugate, as it’s called, exchange genetic material, and then drift apart. Recombination does not require gender. There aren’t boy bacteria and girl bacteria, and bacteria do not have sex—do not recombine segments of their DNA—with every act of reproduction. Sexual plants and animals do. However you bring it about, recombination means that every new being has two parents rather than only one It means that members of the same species—and, except during courtship, the members of most species are solitary and asocial—must arrange a centrally important act that can only be performed in pairs. The two genders might have slightly different goals and strategies, but sex calls, as an absolutely minimum requirement, for cooperation.

Once so powerful an impetus is let out into the world, it might lead, through slow and natural stages, to other kinds of cooperation. Sex brings an entire species together—not just by protecting one another from the cumulative build-up of dangerous mutations, not just by providing new adaptations to a changing environment, but also in the sense of an ongoing, collective enterprise, cross-linking different hereditary lines. This is very different from the asexual practice, where there are many parallel lines of descent, the organisms nearly identical within each line, generation upon generation, and no close relatives between lines.

When sex becomes central to reproduction, the attractiveness of each sex to the other, and the drama of choosing among rivals is moved to center stage. Associated themes include sexual jealousy; real and mock fighting; careful noting of the identities and whereabouts of potential sexual partners and rivals; coercion and rape—all of which in turn lead swiftly, as Darwin pointed out, to the evolution of strange and wonderful appendages, color patterns, and courting behavior that humans often find beautiful, even in members of distantly related species. Darwin thought this sexual selection might be the origin of the human aesthetic sense. Here is a twentieth-century biologist on what sexual selection has brought forth in birds:crests, wattles, ruffs, collars, tippets, trains, spurs, excrescences on wings and bills, tinted mouths, tails of weird or exquisite form, bladders, highly coloured patches of bare skin, elongated plumes, brightly hued feet and legs … The display is nearly always beautiful¹⁰

—especially to the bird of the opposite sex who chooses sexual partners partly on the basis of their good looks. Fashions in beauty then spread rapidly through the population, even if the style isn’t a bit of good in, say, evading predators. Indeed, they spread even if the lifetimes of those who adopt them are thereby considerably shortened, provided the benefit for future generations is sufficiently large. One promising explanation of the showy displays of male birds and fish to the females of their species is that all this is to assure her of his health and prospects.¹¹ Bright plumage and shiny scales demonstrate the absence of an infestation of ticks or mites or fungi, and females—unsurprisingly—prefer to mate with males unburdened by parasites.

——

The sockeye salmon exhaust themselves swimming up the mighty Columbia River to spawn, heroically hurdling cataracts, in a single-minded effort that works to propagate their DNA sequences into future generations. The moment their work is done, they fall to pieces. Scales flake off, fins drop, and soon—often within hours of spawning—they are dead and becoming distinctly aromatic. They’ve served their purpose. Nature is unsentimental. Death is built in.

This is very unlike the far less dramatic asexual reproduction of beings like paramecia, where, pretty closely, remote descendants are genetically identical to their distant ancestors. The ancient organisms can with some justice be described as still alive. With all its manifold advantages, sex brought something else: the end of immortality.

Sexual organisms do not generally reproduce by fission, by splitting in two. The big macroscopic sexual organisms reproduce by making special sex cells, often the familiar sperm and egg, that assemble the genes of the next generation. These cells survive just long enough to accomplish their task, and are hardly able to do anything else at all. In sexual beings, the parent does not evenhandedly distribute its body parts and transmute into two offspring; rather, the parent eventually dies, leaving its world to the next generation, which in its time also dies. Individual asexual organisms die by mistake—when they run out of something, or when they experience a lethal accident. Sexual organisms are designed to die, preprogrammed to do so. Death serves as a poignant reminder of our limitations and frailties—and of the bond with our ancestors who, in a way, died that we might live.

The more active the enzymes devoted to DNA proofreading and repair in big multicellular organisms, the longer the life span tends to be. When these enzymes—themselves of course synthesized under the control of the organism’s DNA—become sparse or inactive, replication errors proliferate and are compounded, and the individual cells increasingly try to implement nonsense instructions. By relaxing the extreme fidelity of its replication, DNA can arrange, at the appropriate moment, for its own death, and that of the organism doing its bidding.

Where sex mandates the death of the individual organism, it provides life to the hereditary line and the species. Still, no matter how many consecutive generations have been recorded of nearly identical asexual beings, eventually the accumulation of deleterious mutations destroys the clone. Eventually, there is a generation where all the individuals are smaller and more feeble, and then you can hear extinction knocking. Sex is the way out. Sex rejuvenates the DNA, revivifies the next generation. There’s a reason we rejoice in it.

A billion years ago, a bargain was struck: the delights of sex in exchange for the loss of personal immortality.¹² Sex and death: You can’t have the former without the latter. Nature, she drives a hard bargain.

——

The first living things had no parents. For about 3 billion years, everyone had one parent, and was pretty close to immortal. Now, many beings have two parents and are unambiguously mortal. There are, so far as we know, no lifeforms that regularly have three parents or more*—although it doesn’t seem much more difficult, in terms of plumbing and allure, to arrange than two. The variety of genetic recombination would be correspondingly greater. And the ability to recognize an error in the message (as the deviant sequence when the three are intercompared) would be much improved. Perhaps on some other planet …

On hearing the love call of the male, the female cowbird promptly adopts a come-hither posture, unmistakably indicating her readiness for copulation. Mature female cowbirds raised in isolation will adopt this posture upon hearing the male’s serenade for the very first time. The male, if he’s raised in isolation, if he’s never heard the cowbird love song in his life, still knows it by heart. The musical score, and information on how to appreciate it, are encoded in their DNA. Perhaps on hearing it the female, at least a little, falls in love with him. Perhaps, on seeing her fetching response to his music, the male, at least a little, falls in love with her.

In contrast to parental care and kin selection, which are so prominent among the birds and mammals, many frogs and fish eat their young. Cannibalism is a commonplace—not just in extraordinary circumstances such as overcrowding or famine, but under normal, everyday conditions: The little ones are plentiful, they’ve gone through all the effort of fattening themselves up into convenient and nutritious packages, only a few need to survive to continue the hereditary line, and an affectionate family life that might exert a restraining influence is lacking. But parental care is not restricted to the birds and mammals. It pops up here and there among fish and even invertebrates. Dung beetle mothers, who have laid their eggs in the “brood balls” they’ve skillfully rolled out of animal feces, dote on their young. And Nile crocodiles, whose powerful jaws can bite a human in two, walk about carefully carrying their little hatchlings, who peer out from between the mothers’ teeth “like sightseers on a bus.”¹³

Even if it is merely genetic sequences working out their self-interest, something that an outside observer might interpret as love has been building in the kingdom of the animals, especially since the extinction of the dinosaurs. With the origin of the primates, it begins its full flowering. It works to bind a species together, in effect to fashion something approaching a common loyalty.

The primacy of reproduction, the sense that the next generation is all, or nearly all, that matters, is made most clear in those many species that promptly die, both sexes, in huge numbers, immediately after conception has occurred and precautions have been taken to safeguard the fertilized eggs. In other species, including our own, the parents play a vital role in protecting and educating the young, and so for them there is life after copulation. Otherwise, the parental generation would have served its purpose, and been hustled off before it came into competition for scarce resources with its own progeny.

The adaptive value of getting DNA strands together has been so substantial that vast changes have been worked in anatomy, physiology, and behavior to accommodate the needs of these molecules. While cooperation was present long before sex—in stromatolite colonies, say, or in the symbiotic relationships of chloroplasts and mitochondria with the cell—sex has introduced a new kind of cooperation, common endeavor, and self-sacrifice into the world. In the differing sexual strategies of male and female, sex has also introduced a novel creative tension—one that cries out for reconciliation and compromise—as well as a potent new motive for competition. Our own species is as good an example as any of the nearly determining role of sex—not just the sex act itself, but all the attendant preparation, consequences, associations, and obsessions—in establishing much of the personality, character, agenda, and drama of life on Earth.

ON IMPERMANENCE

Only

for sleep we come,

for dreams.

Lie! It is a lie.

We come to live on Earth.

As a weed we become

each springtime,

swell green, our hearts

open,

the body makes a few flowers

and drops away withered somewhere.

Poems of the Aztec Peoples¹⁴

* In vitro fertilization is of course still sex.* Although strands from two different dead bacteria might, on rare occasions, be incorporated by a live bacterium

Chapter 9

WHAT THIN PARTITIONS …

How instinct varies in the grovelling swine,

Compar’d, half-reasoning elephant, with thine!

’Twixt that, and reason, what a nice barrier,

Forever sep’rate, yet forever near!

Remembrance and reflection how ally’d!

What thin partitions sense from thought divide!

ALEXANDER POPE,

Essay on Man¹

Most people would rather be alive than dead. But why? It’s hard to give a coherent answer. An enigmatic “will to live” or “life force” is often cited. But what does that explain? Even victims of atrocious brutality and intractable pain may retain a longing, sometimes even a zest, for life. Why, in the cosmic scheme of things, one individual should be alive and not another is a difficult question, an impossible question, perhaps even a meaningless question. Life is a gift that, of the immense number of possible but unrealized beings, only the tiniest fraction are privileged to experience. Except in the most hopeless of circumstances, hardly anyone is willing to give it up voluntarily—at least until very old age is reached

A similar puzzlement attaches to sex. Very few, at least today, have sex for the conscious purpose of propagating the species or even their own personal DNA; and such a decision for such a purpose, coolly and rationally entered into, is exceedingly rare in adolescents. (For most of the tenure of humans on Earth, the average person did not live much beyond adolescence.) Sex is its own reward.

Passions for life and sex are built into us, hardwired, pre-programmed. Between them, they go a long way toward arranging for many offspring with slightly differing genetic characteristics, the essential first step for natural selection to do its work. So we are the mostly unconscious tools of natural selection, indeed its willing instruments. As deeply as we can go in assessing our own feelings, we do not recognize any underlying purpose. All that is added later. All the social and political and theological justifications are attempts to rationalize, after the fact, human feelings that are at the same time utterly obvious and profoundly mysterious.

Now imagine us with no interest at all in “explaining” such matters, no weakness for reason and contemplation. Suppose you unquestioningly accepted these predispositions for surviving and reproducing, and spent your time solely in fulfilling them. Might that be something like the state of mind of most beings? Every one of us can recognize these two modes coexisting within us. A moment of introspection is often all it takes. Religious writers have described them as our animal and spiritual states. In everyday speech, the distinction is between feeling and thought. Inside our heads there seem to be two different ways of dealing with the world, the second, in the sweep of evolutionary time, arisen in earnest only lately.

——

Consider the world of the tick.² Plumbing aside, what must it do to reproduce its kind? Ticks often have no eyes. Males and females find each other by aroma, olfactory cues called sex pheromones. For many ticks the pheromone is a molecule called 2,6-dichlorophenol. If C stands for a carbon atom, H for hydrogen, O for oxygen, and Cl for chlorine, this ring-shaped molecule can be written C₆H₃OHCl₂ A little 2,6-dichlorophenol in the air and ticks go wild with passion.³

After mating, the female climbs up a bush or shrub and out onto a twig or leaf. How does she know which way is up? Her skin can sense the direction from which light is coming, even if she cannot generate an optical image of her surroundings. Poised out on the leaf or twig, exposed to the elements, she waits. Conception has not yet occurred. The sperm cells within her are neatly encapsulated; they’ve been put in long-term storage. She may wait for months or even years without eating. She is very patient.

What she’s waiting for is a smell, a whiff of another specific molecule, perhaps butyric acid, which can be written C₃H₇COOH. Many mammals, including humans, give off butyric acid from their skin and sexual parts. A small cloud of the stuff follows them around like cheap perfume. It’s a sex attractant for mammals. But ticks use it to find food for prospective mothers. Smelling the butyric acid wafting up from below, the tick lets go. She drops from her perch and falls through the air, legs akimbo. If she’s lucky, she lands on the passing mammal. (If not, she falls to the ground, shakes herself off, and tries to find another bush to climb.)

Clinging to the fur of her unsuspecting host, she works her way through the thicket to find a less hairy spot, a patch of nice warm bare skin. There, she punctures the epidermis and drinks her fill of blood.*

The mammal may feel a sting and rub the tick off, or intently comb through its hair and pick it off. Rats may spend as much as one-third their waking hours grooming themselves. Ticks can draw a great deal of blood, they secrete neurotoxins, they carry disease microbes. They’re dangerous. Too many of them on a mammal at the same time can lead to anemia, loss of appetite, and death. Monkeys and apes meticulously search through each other’s fur; this is one of their principal cultural idioms. When they find a tick, they remove it with their precision grip and eat it. As a result, they are remarkably free from such parasites in the wild.

If the tick has avoided the hazards of grooming, and has become engorged with blood, she drops heavily to the ground. Thus fortified, she unseals the chamber with the stored sperm cells, lays the fertilized eggs in the soil (perhaps ten thousand of them) and dies—her descendants left to continue the cycle.

Note how simple are the sensory abilities required of the tick. They may have been feeding on reptile blood before the first dinosaurs evolved, but their repertoire of essential skills remains fairly meager. The tick must be crudely responsive to sunlight so she knows which way is up; she must be able to smell butyric acid so she knows when to fall animalward; she must be able to sense warmth; she must know how to inch her way around obstacles This is not asking much. Today we have very small photocells easily able to find the sun on a cloudless day. We have many chemical analytic instruments that can detect small amounts of butyric acid. We have miniaturized infrared sensors that sense heat. Indeed, all three such devices have been flown on spacecraft to explore other worlds—the Viking missions to Mars, for example. A new generation of mobile robots being developed for planetary exploration is now able to amble over and around large obstacles. Some progress in miniaturization would be needed, but we are not very far from being able to build a little machine that could duplicate—indeed far surpass—the central abilities of the tick to sense the outside world. And we certainly could equip it with a hypodermic syringe. (Harder for us to duplicate just yet would be its digestive tract and reproductive system. We are very far from being able to simulate from scratch the biochemistry of a tick.)

What would it be like inside the tick’s brain? You would know about light, butyric acid, 2,6-dichlorophenol, the warmth of a mammal’s skin, and obstacles to clamber around or over. You have no image, no picture, no vision of your surroundings; you are blind. You are also deaf. Your ability to smell is limited. You are certainly not doing much in the way of thinking. You have a very limited view of the world outside. But what you know is sufficient for your purpose.⁴

——

There’s a thump on the window and you look up. A moth has careened headlong into the transparent glass. It had no idea the glass was there: There have been things like moths for hundreds of millions of years, and glass windows only for thousands. Having bumped its head against the window, what does the moth do next? It bumps its head against the window again. You can see insects repeatedly throwing themselves against windows, even leaving little bits of themselves on the glass, and never learning a thing from the experience.

Clearly there’s a simple flying program in their brains, and nothing that allows them to take notice of collisions with invisible walls. There’s no subroutine in that program that says, “If I keep bumping into something, even if I can’t see it, I should try to fly around it.” But developing such a subroutine carries with it an evolutionary cost, and until lately there were no penalties levied on moths without it. They also lack a general-purpose problem-solving ability equal to this challenge. Moths are unprepared for a world with windows.

If we have here an insight into the mind of the moth, we might be forgiven for concluding that there isn’t much mind there. And yet, can’t we recognize in ourselves—and not just in those of us gripped by a pathological repetition-compulsion syndrome—circumstances in which we keep on doing the same stupid thing, despite irrefutable evidence it’s getting us into trouble?

We don’t always do better than moths. Even heads of state have been known to walk into glass doors. Hotels and public buildings now affix large red circles or other warning signs on these nearly invisible barriers. We too evolved in a world without plate glass. The difference between the moths and us is that only rarely do we shake ourselves off and then walk straight into the glass door again.

Like many other insects, caterpillars follow scent trails left by their fellows. Paint the ground with an invisible circle of scent molecule and put a few caterpillars down on it. Like locomotives on a circular track, they’ll go around and around forever—or at least until they drop from exhaustion. What, if anything, is the caterpillar thinking? “The guy in front of me seems to know where he’s going, so I’ll follow him to the ends of the Earth”? Almost always, following the scent trail gets you to another caterpillar of your species, which is where you want to be. Circular trails almost never occur in Nature—unless some wiseacre scientist shows up. And so this weakness in their program almost never gets caterpillars into trouble. Again we detect a simple algorithm and no hint of an executive intelligence evaluating discordant data.

When a honeybee dies it releases a death pheromone, a characteristic odor that signals the survivors to remove it from the hive. This might seem a supreme final act of social responsibility. The corpse is promptly pushed and tugged out of the hive. The death pheromone is oleic acid [a fairly complex molecule, CH₃(CH₂)₇CH = CH(CH₂)₇COOH, where = stands for a double chemical bond]. What happens if a live bee is dabbed with a drop of oleic acid? Then, no matter how strapping and vigorous it might be, it is carried “kicking and screaming” out of the hive.⁵ Even the queen bee, if she’s painted with invisible amounts of oleic acid, will be subjected to this indignity.

Do the bees understand the danger of corpses decomposing in the hive? Are they aware of the connection between death and oleic acid? Do they have any idea what death is? Do they think to check the oleic acid signal against other information, such as healthy, spontaneous movement? The answer to all these questions is, almost certainly, No. In the life of the hive there’s no way that a bee can give off a detectable whiff of oleic acid other than by dying. Elaborate contemplative machinery is unnecessary. Their perceptions are adequate for their needs.

Does the dying insect make a special last effort to generate oleic acid, to benefit the hive? More likely, the oleic acid derives from a malfunction of fatty acid metabolism around the time of death, which is recognized by the highly sensitive chemical receptors in the survivors. A strain of bees that had a slight tendency to manufacture a death pheromone would do better than one in which decomposing, disease-ridden dead bodies were littering the hive. And this would be true even if no other bee in the hive were a close relative of the recently departed. On the other hand, since they are all close relatives, special manufacture of a death pheromone can be understood perfectly well in terms of kin selection.

——

So here’s a bejeweled insect, elegantly architectured, prancing among the dust grains in the noonday sun. Does it have any emotions, any consciousness? Or is it only a subtle robot made of organic matter, a carbon-based automaton packed with sensors and actuators, programs and subroutines, all ultimately manufactured according to the DNA instructions? (Later, we will want to look more closely at what “only” means.) We might be willing to grant the proposition that insects are robots; there’s no evidence, so far as we know, that compellingly argues the contrary; and most of us have no deep emotional attachments to insects.

In the first half of the seventeenth century, René Descartes, the “father” of modern philosophy, drew just such a conclusion. Living in an age when clocks were at the cutting edge of technology, he imagined insects and other creatures as elegant, miniaturized bits of clockwork—“a superior race of marionettes,” as Huxley described it,⁶ “which eat without pleasure, cry without pain, desire nothing, know nothing, and only simulate intelligence as a bee simulates a mathematician” (in the geometry of its hexagonal honeycombs). Ants do not have souls, Descartes argued; automatons are owed no special moral obligations.

What then are we to conclude when we find similar very simple behavioral programs, unsupervised by any apparent central executive control, in much “higher” animals? When a goose egg rolls out of the nest, the mother goose will carefully nudge it back in. The value of this behavior for goose genes is clear. Does the mother goose who has been incubating her eggs for weeks understand the importance of retrieving one that has rolled away? Can she tell if one is missing? In fact, she will retrieve almost anything placed near the nest, including ping-pong balls and beer bottles. She understands something, but, we might say, not enough.If a chick is tied to a peg by one leg, it peeps loudly. This distress call makes the mother hen run immediately in the direction of the sound with ruffled plumage, even if the chick is invisible. As soon as she catches sight of the chick, she begins to peck furiously at an imaginary antagonist. But if the fettered chick is set before the mother hen’s eyes under a glass bell, so that she can see it but not hear its distress call, she is not in the least disturbed by the sight of him. … The perceptual cue of peeping normally comes indirectly from an enemy who is attacking the chick. According to plan, this sensory cue is extinguished by the effector cue of beak thrusts, which chase the foe away. The struggling, but not-peeping chick is not a sensory cue that would release a specific activity.⁷

Male tropical fish show fighting readiness when they see the red markings of other males of their species. They also get agitated when they glimpse a red truck out the window. Humans find themselves sexually aroused by looking at certain arrangements of very small dots on paper or celluloid or magnetic tape. They pay money to look at these patterns.

So now where are we? Descartes was prepared to grant that fish and poultry are also subtle automatons, also soulless. But then what about humans?

Descartes was here treading on dangerous ground. He had before him the chastening example of the aged Galileo, threatened with torture by the self-styled “Holy Inquisition” for maintaining that the Earth turns once each day, rather than the view, clearly expressed in the Bible, that the Earth is stationary and the heavens race around us once each day. The Roman Catholic Church was quite prepared to coerce conformity—to intimidate, torture, and murder to force people to think as it did. At the very beginning of Descartes’s century, the Church had burned the philosopher Giordano Bruno alive because he thought for himself, spoke out, and would not recant. And here, the proposal that animals are clockwork automatons was a far riskier and theologically more sensitive matter than whether the Earth turns—touching not peripheral but central dogmas: free will, the existence of the soul. As on other issues, Descartes walked a fine line.

We “know” we are more than just a set of extremely complex computer programs. Introspection tells us that. That’s the way it feels. And so Descartes, who attempted a thorough, skeptical examination of why he should believe anything, who made famous the proposition Cogito, ergo sum (“I think, therefore I am”), granted immortal souls to humans, and to no one else on Earth.

But we, who live in a more enlightened time, when the penalties for disquieting ideas are less severe, not only may, but have an obligation to, inquire further—as many since Darwin have done. What, if anything, do the other animals think? What might they have to say if properly interrogated? When we examine some of them carefully, do we not find evidence of executive controls weighing alternatives, of branched contingency trees? When we consider the kinship of all life on Earth, is it plausible that humans have immortal souls and all other animals do not?

The moth doesn’t need to know how to fly around the pane of glass, or the goose to retrieve eggs but not beer bottles—again because glass windows and beer bottles have not been around long enough to have been a significant factor in the natural selection of insects and birds. The programs, circuits and behavioral repertoires are simple when no benefit accrues from their being complex. Complex mechanisms evolve when the simple ones will not do.

In Nature, the goose’s egg-retrieval program is adequate. But when the goslings hatch, and especially just before they’re ready to leave the nest, the mother is delicately attuned to the nuances of their sounds, looks, and (perhaps) smells. She has learned about her chicks. Now, she knows her own very well, and would not confuse them with someone else’s goslings, however similar they may seem to a human observer.

In species of birds where mix-ups are likely, where the young may fledge and mistakenly land in a neighboring nest, the machinery for maternal recognition and discrimination is even more elaborate. The goose’s behavior is flexible and complex when rigid and simple behavior is too dangerous, too likely to lead to error; otherwise it is rigid and simple. The programs are parsimonious, no more complex than they need be—if only the world does not produce too much novelty, too many windows and beer bottles.

Consider our prancing insect again. It can see, walk, run, smell, taste, fly, mate, eat, excrete, lay eggs, metamorphose. It has internal programs for accomplishing these functions—contained in a brain of mass, perhaps, only a milligram—and specialized, dedicated organs for carrying the programs out. But is that all? Is there anyone in charge, anyone inside, anyone controlling all these functions? What do we mean by “anyone”? Or is the insect just the sum of its functions, and nothing else, with no executive authority, no director of the organs, no insect soul?

You get down on your hands and knees, look at the insect closely, and you see it cock its head, triangulating you, trying to get a sense of this immense, looming, three-dimensional monster before it. The fly strides unconcernedly; you lift the rolled-up newspaper and it quickly buzzes off. You turn on the light and the cockroach stops dead in its tracks, regarding you keenly Move toward it and it scampers into the woodwork. We “know” such behavior is due to simple neuronal subroutines. Many scientists get nervous if you ask about the consciousness of a housefly or a roach. But sometimes you get an eerie feeling that the partitions separating programs from awareness may be not just thin, but porous.

We know the insect decides who to eat, who to run away from, who to find sexually attractive. On the inside, within its tiny brain, does it have no perception of making choices, no awareness of its own existence? Not a milligram’s worth of self-consciousness? Not a hint of a hope for the future? Not even a little satisfaction at a day’s work well done? If its brain is one millionth the mass of ours, shall we deny it one millionth of our feelings and our consciousness? And if, after carefully weighing such matters, we insist it is still “only” a robot, how sure are we that this judgment does not apply as well to us?

We can recognize the existence of such subroutines precisely because of their unbending simplicity. But if instead we had before us an animal brimming over with complex judgments, branched contingency trees, unpredictable decisions, and a strong executive program, would it seem to us that there is more here than just an elaborate, exquisitely miniaturized computer?

The honeybee scout returns to the hive from a foraging expedition and “dances,” rapidly crawling in a particular, fairly complex pattern over the honeycomb. Pollen or nectar may adhere to her body, and she may regurgitate some of her stomach contents for her eager sisters. All this is done in complete darkness, her motions monitored by the spectators through their sense of touch. Given only this information, a swarm of bees then flies out of the hive in the proper direction to the proper distance to a food supply they’ve never visited as effortlessly as if this was their daily, familiar commute from home to work. They partake of the meal described to them. All this occurs more often when food is scarce or the nectar especially sweet.⁸ How to encode the location of a field of flowers into the language of dance, and how to decode the choreography is knowledge present in the hereditary information stored inside the insect. Maybe they are “only” robots, but if so these robots have formidable capabilities.

When we characterize such beings as only robots, we are also in danger of losing sight of the possibilities in robotics and artificial intelligence over the next few decades. Already, there are robots that read sheet music and play it on a keyboard, robots that translate pretty well between two very different languages, robots that learn from their own experiences—codifying rules of thumb never taught to them by their programmers. (In chess, for example, they might learn that it is generally better to position bishops near the center than near the periphery of the board, and then teach themselves circumstances in which an exception to this rule is warranted.) Some open-loop chess-playing robots can defeat all but a handful of human chess masters. Their moves surprise their programmers. Their completed games are routinely analyzed by experts who speculate about what the robot’s “strategy,” “goals,” and “intentions” must have been. If you have a large enough pre-programmed behavioral repertoire and if you are able to learn enough from experience, don’t you begin to appear to an outside observer as if you’re a conscious being making voluntary choices—whatever may or may not be going on inside your head (or wherever you keep your neurons)?⁹

And when you have a massive collection of mutually integrated programs, capability for learned behavior, data-processing prowess, and means of ranking competing programs, might it not start feeling, on the inside, a little bit like thinking? Might our penchant for imagining someone inside pulling the strings of the animal marionette be a peculiarly human way of viewing the world?* Could our sense of executive control over ourselves, of pulling our own strings, be likewise illusory—at least most of the time, for most of what we do? How much are we really in charge of ourselves? And how much of our actual everyday behavior is on automatic pilot?

Among the many human feelings that, although culturally mediated, may be fundamentally preprogrammed, we might list sexual attraction, falling in love, jealousy, hunger and thirst, horror at the sight of blood, fear of snakes and heights and “monsters,” shyness and suspicion of strangers, obedience to those in authority, hero worship, dominance of the meek, pain and weeping, laughter, the incest taboo, the infant’s smiling delight at seeing members of its family, separation anxiety, and maternal love. There is a complex of emotions attached to each, and thinking has very little to do with any of them. Surely, we can imagine a being whose internal life is nearly wholly composed of such feelings, and nearly devoid of thought.

——

The spider builds her web near our porch light. The fine, tough thread reels out from her spinneret. We first notice the web glistening with tiny droplets after a rainstorm, the proprietor repairing a damaged circumferential strut. The elegant, concentric, polygonal pattern is carefully stabilized with a single guy thread extending to the cowl of the lamp itself, and another to a nearby railing. She repairs the web even in darkness and foul weather. At night, when the light is on, she sits at the very center of her construction, awaiting the hapless insect who is attracted by the light and whose eyesight is so poor that the web is quite invisible. The moment one becomes entangled, news of this event travels to her in waves along the threads. She rushes down a radial strut, stings it, quickly wraps it in a white cocoon, packaging it for future use, and rushes back to her command center—composed, a marvel of efficiency, not even, as far as we can see, a little out of breath.

How does she know to design, construct, stabilize, repair, and utilize this elegant web? How does she know to build it near the lamp, to which the insects are attracted? Did she scamper all over the house tallying the abundance of insects in various potential campsites? How could her behavior be pre-programmed, since artificial lights have been invented much too recently to be taken account of in the evolution of spiders?

When spiders are given LSD or other consciousness-altering drugs, their webs become less symmetrical, more erratic, or, we might say, less obsessive, more freeform—but also less effective in catching insects. What has a tripping spider forgotten?

Maybe its behavior is entirely pre-programmed in its ACGT code. But then, couldn’t much more complex information be locked away in a much longer, much more elaborate code? Or maybe some of this information is learned from past adventures in spinning and repairing webs, immobilizing and eating prey. But then look how small that spider’s brain is. How much more sophisticated behavior might emerge out of the experience of a much larger brain?

The web is anchored opportunistically to a local geometry of lamp cowling, metal railing, and wood siding. That could not per se have been pre-programmed. There must have been some element of choice, of decision making, of connecting a hereditary predisposition to an environmental circumstance never before encountered.

Is she “only” an automaton, unquestioningly performing actions that seem to her the most natural thing in the world—and being rewarded, her behavior reinforced by an ample supply of food? Or might there be a component of learning, decision making, and self-consciousness?

Adopting high standards of engineering precision, she spins her web now. She reaps the reward later, maybe much later. She patiently waits. Does she know what she’s waiting for? Does she dream of succulent moths and foolish mayflies? Or does she wait with her mind a blank, idling, thinking of nothing at all—until the telltale tug sends her scurrying down one of the radial struts to sting the struggling insect before it frees itself and escapes? Are we really sure she doesn’t have even a faint and intermittent spark of consciousness?

We would guess that some rudimentary awareness flickers in the most humble creatures, and that with increasing neuronal architecture and brain complexity, consciousness grows. “When a dog runs,” said the naturalist Jakob von Uexküll, “the dog moves his legs; when a sea urchin runs, the legs move the sea urchin.”¹⁰ But even in humans, thinking is often a subsidiary state of consciousness.

If it were possible to peer into the psyche of a spider or a goose, we might detect a kaleidoscopic progression of inclinations—and maybe some premonitions of conscious choice, actions selected from a menu of possible alternatives. What individual nonhuman organisms may perceive as their motivations, what they feel is happening inside their bodies, is for us one of the nearly inaudible counterpoints to the music of life.

When an animal goes out to seek food, it often does so according to a definite pattern. A random search is inefficient, because the path would turn back on itself many times; the same places would then be examined again and again. Instead, while the animal may dart off to left and right, the general search pattern is almost always progressive forward motion. The animal finds itself on new ground. The search for food becomes an exercise in exploration. A passion for discovery is hardwired. It’s something we like to do for its own sake, but it brings rewards, aids survival, and increases the number of offspring.

Perhaps animals are almost pure automatons—with urges, instincts, hormonal rushes, driving them toward behavior which in turn is carefully honed and selected to aid the propagation of a particular genetic sequence. Perhaps states of consciousness, no matter how vivid, are as Huxley suggested, “immediately caused by molecular changes in the brain substance.” But from the point of view of the animal, it must seem—as it does with us—natural, passionate, and occasionally even thought out. Perhaps a flurry of impulses and intersecting subroutines at times feels something like the exercise of free will. Certainly the animal cannot much have an impression of being impelled against its will. It voluntarily chooses to behave in the manner dictated by its contending programs. Mainly, it’s just following orders.

So when the days become long enough, it feels an unfocused restlessness, something like spring fever. It hasn’t thought through conception, gestation, the optimum season for the birth of the young and the continuance of its genetic sequences; all that is far beyond its abilities. But from the inside it may well feel as though the weather is intoxicating, life is tempestuous, and moonlight becomes you.

——

We do not mean to be patronizing. The depth of understanding exhibited by our fellow creatures is of course limited. So is ours. We also are at the mercy of our feelings. We too are profoundly ignorant about what motivates us. Some of those beings have, as familiar aspects of their everyday lives, sensibilities wholly absent in humans. Other beings have different tastes and appreciations of the outside world—“To a worm in horseradish, the horseradish seems sweet,” as an old Yiddish folk adage has it. Beyond that, the horseradish worm lives in a world of smells, tastes, textures, and other sensations unknown to us.

Bumblebees detect the polarization of sunlight, invisible to uninstrumented humans; pit vipers sense infrared radiation and detect temperature differences of 0.01°C at a distance of half a meter; many insects can see ultraviolet light; some African freshwater fish generate a static electric field around themselves and sense intruders by slight perturbations induced in the field; dogs, sharks, and cicadas detect sounds wholly inaudible to humans; ordinary scorpions have micro-seismometers on their legs so they can detect in pitch darkness the footsteps of a small insect a meter away; water scorpions sense their depth by measuring the hydrostatic pressure; a nubile female silkworm moth releases ten billionths of a gram of sex attractant per second, and draws to her every male for miles around; dolphins, whales, and bats use a kind of sonar for precision echo-location.

The direction, range, amplitude, and frequency of sounds reflected back to echo-locating bats are systematically mapped onto adjacent areas of the bat brain. How does the bat perceive its echo-world? Carp and catfish have taste buds distributed over most of their bodies, as well as in their mouths; the nerves from all these sensors converge on massive sensory processing lobes in their brains, lobes unknown in other animals. How does a catfish view the world? What does it feel like to be inside its brain? There are reported cases in which a dog wags its tail and greets with joy a man it has never met before; he turns out to be the long-lost identical twin of the dog’s “master,” recognizable by his odor. What is the smell-world of a dog like? Magnetotactic bacteria contain within them tiny crystals of magnetite—an iron mineral known to early sailing ship navigators as lodestone. The bacteria literally have internal compasses that align them along the Earth’s magnetic field. The great churning dynamo of molten iron in the Earth’s core—as far as we know, entirely unknown to uninstrumented humans—is a guiding reality for these microscopic beings. How does the Earth’s magnetism feel to them? All these creatures may be automatons, or nearly so, but what astounding special powers they have, never granted to humans, or even to comic book superheroes. How different their view of the world must be, perceiving so much that we miss.

Each species has a different model of reality mapped into its brain. No model is complete. Every model misses some aspects of the world. Because of this incompleteness, sooner or later there will be surprises—perceived, perhaps, as something like magic or miracles. There are different sensory modalities, different detection sensitivities, different ways the various sensations are integrated into a dynamic mental map of … a snake, say, in full hunting slither.

But Descartes was unimpressed. He wrote to the Marquis of Newcastle:I know, indeed, that brutes do many things better than we do, but I am not surprised at it; for that, also, goes to prove that they act by force of nature and by springs, like a clock, which tells better what the hour is than our judgment can inform us.¹¹

——

As life evolved, the repertoire of feelings expanded. Aristotle thought that “in a number of animals we observe gentleness or fierceness, mildness or cross-temper, courage or timidity, fear or confidence, high spirit or low cunning, and, with regard to intelligence, something equivalent to sagacity.”¹² Emotions that Darwin argued are manifested by at least some mammals other than humans—chiefly dogs, horses, and monkeys—include pleasure, pain, happiness, misery, terror, suspicion, deceit, courage, timidity, sulkiness, good temper, revenge, selfless love, jealousy, hunger for affection and praise, pride, shame, modesty, magnanimity, and a sense of humor.¹³

And at some point, probably long before the first humans, a new set of emotions—curiosity, insight, the pleasures of learning and teaching—also slowly emerged. Neuron by neuron, the partitions began to go up.

ARE ANIMALS MACHINES? FOUR VIEWS

A Seventeenth-Century View: Descartes:

[A]s you may have seen in the grottoes and the fountains in royal gardens, the force with which the water issues from its reservoir is sufficient to move various machines, and even to make them play instruments, or pronounce words according to the different disposition of the pipes which lead the water …

The external objects which, by their mere presence, act upon the organs of the senses; and which, by this means, determine the corporal machine to move in many different ways, according as the parts of the brain are arranged, are like the strangers who, entering into some of the grottoes of these waterworks, unconsciously cause the movements which take place in their presence. For they cannot enter without treading upon certain planks so arranged that, for example, if they approach a bathing Diana, they cause her to hide among the reeds; and if they attempt to follow her, they see approaching a Neptune, who threatens them with his trident; or if they try some other way, they cause some other monster, who vomits water into their faces, to dart out; or like contrivances, according to the fancy of the engineers who have made them. And lastly, when the rational soul is lodged in this-machine, it will have its principal seat in the brain, and will take the place of the engineer, who ought to be in that part of the works with which all the pipes are connected, when he wishes to increase, or to slacken, or in some way to alter their movements …

All the functions which I have attributed to this machine (the body), as the digestion of food, the pulsation of the heart and of the arteries; the nutrition and the growth of the limbs; respiration, wakefulness, and sleep; the reception of light, sounds, odours, flavours, heat, and such like qualities, in the organs of the external senses; the impression of the ideas of these in the organ of common sense and in the imagination; the retention, or the impression, of these ideas on the memory; the internal movements of the appetites and the passions; and lastly, the external movements of all the limbs, which follow so aptly, as well as the action of the objects which are presented to the senses, as the impressions which meet in the memory, that they imitate as nearly as possible those of a real man: I desire, I say, that you should consider that these functions in the machine naturally proceed from the mere arrangement of its organs, neither more nor less than do the movements of a clock, or other automaton, from that of its weights and its wheels; so that, so far as these are concerned, it is not necessary to conceive any other vegetative or sensitive soul, nor any other principle of motion, or of life.¹⁴

An Eighteenth-Century View: Voltaire:

What a pitiful, what a sorry thing to have said that animals are machines bereft of understanding and feeling, which perform their operations always in the same way, which learn nothing, perfect nothing, etc.!

What! that bird which makes its nest in a semi-circle when it is attaching it to a wall, which builds it in a quarter circle when it is in an angle, and in a circle upon a tree; that bird acts always in the same way? That hunting-dog which you have disciplined for three months, does it not know more at the end of this time than it knew before your lessons? Does the canary to which you teach a tune repeat it at once? Do you not have to spend a considerable time in teaching it? Have you not seen that it has made a mistake and that it corrects itself?

Is it because I speak to you, that you judge that I have feeling, memory, ideas? Well, I do not speak to you; you see me going home looking disconsolate, seeking a paper anxiously, opening the desk where I remember having shut it, finding it, reading it joyfully. You judge that I have experienced the feeling of distress and that of pleasure, that I have memory and understanding.

Bring the same judgment to bear on this dog which has lost its master, which has sought him on every road with sorrowful cries, which enters the house agitated, uneasy, which goes down the stairs, up the stairs, from room to room, which at last finds in his study the master it loves, and which shows him its joy by its cries of delight, by its leaps, by its caresses.¹⁵

A Nineteenth-Century View: Huxley:

Consider what happens when a blow is aimed at the eye. Instantly, and without our knowledge or will, and even against the will, the eyelids close. What is it that happens? A picture of the rapidly-advancing fist is made upon the retina at the back of the eye. The retina changes this picture into an affection of a number of the fibres of the optic nerve; the fibres of the optic nerve affect certain parts of the brain; the brain, in consequence, affects those particular fibres of the seventh nerve which go to the orbicular muscle of the eyelids; the change in these nerve-fibres causes the muscular fibres to alter their dimensions, so as to become shorter and broader; and the result is the closing of the slit between the two lids, round which these fibres are disposed. Here is a pure mechanism, giving rise to a purposive action, and strictly comparable to that by which Descartes supposes his waterwork Diana to be moved. But we may go further, and inquire whether our volition, in what we term voluntary action, ever plays any other part than that of Descartes’ engineer, sitting in his office, and turning this tap or the other, as he wishes to set one or another machine in motion, but exercising no direct influence upon the movements of the whole …

Descartes pretends that he does not apply his views to the human body, but only to an imaginary machine which, if it could be constructed, would do all that the human body does; throwing a sop to Cerberus unworthily; and uselessly, because Cerberus was by no means stupid enough to swallow it …

… [W]hat living man, if he had unlimited control over all the nerves supplying the mouth and larynx of another person, could make him pronounce a sentence? Yet, if one has anything to say, what is easier than to say it? We desire the utterance of certain words: we touch the spring of the word-machine, and they are spoken. Just as Descartes’ engineer, when he wanted a particular hydraulic machine to play, had only to turn a tap, and what he wished was done. It is because the body is a machine that education is possible. Education is the formation of habits, a superinducing of an artificial organisation upon the natural organisation of the body; so that acts, which at first required a conscious effort, eventually became unconscious and mechanical. If the act which primarily requires a distinct consciousness and volition of its details, always needed the same effort, education would be an impossibility.

According to Descartes, then, all the functions which are common to man and animals are performed by the body as a mere mechanism, and he looks upon consciousness as the peculiar distinction of the “chose pensante,” of the “rational soul,” which in man (and in man only, in Descartes’ opinion) is superadded to the body. This rational soul he conceived to be lodged in the pineal gland, as in a sort of central office; and here, by the intermediation of the animal spirits, it became aware of what was going on in the body, or influenced the operations of the body. Modern physiologists do not ascribe so exalted a function to the little pineal gland, but, in a vague sort of way, they adopt Descartes’ principle, and suppose that the soul is lodged in the cortical part of the brain—at least this is commonly regarded as the seat and instrument of consciousness.

.. [T]hough we may see reason to disagree with Descartes’ hypothesis that brutes are unconscious machines, it does not follow that he was wrong in regarding them as automata. They may be more or less conscious, sensitive, automata; and the view that they are such conscious machines is that which is implicitly, or explicitly, adopted by most persons. When we speak of the actions of the lower animals being guided by instinct and not by reason, what we really mean is that, though they feel as we do, yet their actions are the results of their physical organisation. We believe, in short, that they are machines, one part of which (the nervous system) not only sets the rest in motion, and co-ordinates its movements in relation with changes in surrounding bodies, but is provided with special apparatus, the function of which is the calling into existence of those states of consciousness which are termed sensations, emotions, and ideas. I believe that this generally accepted view is the best expression of the facts at present known.

… It is quite true that, to the best of my judgment, the argumentation which applies to brutes holds equally good of men; and, therefore, that all states of consciousness in us, as in them, are immediately caused by molecular changes of the brain-substance. It seems to me that in men, as in brutes, there is no proof that any state of consciousness is the cause of change in the motion of the matter of the organism. If these positions are well based, it follows that our mental conditions are simply the symbols in consciousness of the changes which take place automatically in the organism; and that, to take an extreme illustration, the feeling we call volition is not the cause of a voluntary act, but the symbol of that state of the brain which is the immediate cause of that act. We are conscious automata …¹⁶

A Twentieth-Century View: James L. and Carol G. Gould:

In considering the issue of mental experiences in animals, we have begun to wonder if the implicit assumption that humans are almost wholly conscious and aware (and hence fully competent to evaluate our cognitively less sophisticated animal brethren) is correct. Could it be that the degree to which conscious thinking is involved in the everyday lives of most people is greatly overestimated? We know already that much of our learned behavior becomes hardwired: despite the painfully difficult process of learning the task originally, who has to concentrate consciously as an adult on how to walk or swim, tie a shoe, write words, or even drive a car along a familiar route? Certain linguistic behavior, too, falls into such patterns. Michael Gazzaniga, for instance, tells the story of a former physician who suffered from a left (linguistic) hemisphere lesion so serious that he could not form even simple three-word sentences. And yet, when a certain highly touted but ineffective patent medicine was mentioned, he would launch into a well-worn and perfectly grammatical five-minute tirade on its evils. This set piece had been stored on the undamaged right side (along with the usual collection of songs, poetry, and epigrams) as a motor tape requiring no conscious linguistic manipulation to deliver.

… Indeed, what evidence is there that those sublime intellectual events known as “inspiration” involve any conscious thought? Most often our best ideas are served up to us out of our unconscious while we are thinking or doing something perfectly irrelevant. Inspiration probably depends on some sort of repetitive and time-consuming pattern-matching program which runs imperceptibly below the level of consciousness searching for plausible matches.

It strikes us that a skeptical and dispassionate extraterrestrial ethologist studying our unendearing species might reasonably conclude that Homo sapiens are, for the most part, automatons with overactive and highly verbal public relations departments to apologize for and cover up our foibles.¹⁷

* It’s not the taste of the blood that attracts her, but the warmth If she drops onto a butyric acid-scented toy balloon filled with warm water, she will readily puncture it and, an inept Dracula, gorge herself on tap water* One promising finding in artificial intelligence is the discovery that distributed data processing—many small computers working in parallel without much of a central processing unit—does very well, by some standards better than the largest and fastest lone computer Many little minds working in tandem may be superior to one big mind working alone

Chapter 10

THE NEXT-TO-LAST REMEDY

When all the world is overcharged with inhabitants,

then the last remedy of all is war …

THOMAS HOBBES,

Leviathan, II, 30¹

Once organisms get really good at sex, once they evolve the plumbing and the passion for it, there gets to be a danger: So many competent, DNA-exchanging beings may be born that they will improvidently gobble up all the food or nutrients or prey, and then almost everyone, including their close relatives, will die. This must have occurred innumerable times in the history of life.

Take a being as modest as a bacterium, weighing in at a trillionth of a gram, and let it reproduce with no impediments. In the second generation there will be two bacteria; in the third generation, four; in the fourth generation, eight; and so on. If we imagine that none of those offspring die, then in 100 generations they will collectively weigh as much as a mountain; in 135 generations, as much as the Earth; in 150 generations, as much as the Sun; and in 185 generations, as much as the Milky Way galaxy.

Of course, such prodigious increases in mass are arithmetic exercises only. They could never occur in the real world. For one thing, the replicating microbes would soon run out of food. Your descendants cannot weigh as much as a mountain if there’s not a mountain’s worth of food to eat—much less an Earth’s worth or a Sun’s or a galaxy’s. There is only so much food available. Thus, your descendants will quite soon be in competition with one another for scarce resources. But because of the enormous power of exponential reproduction, an organism with even a slight advantage in finding or utilizing food rapidly supplants the competition (or at least its descendants do). Fast reproducers generate large populations, and competition for resources; they provide the raw material for a natural selection that efficiently magnifies small differences in fitness, differences that might be too small or subtle for even the most skilled naturalist to notice. This was the central argument of Darwin’s unpublished 1844 manuscript on evolution, and of his article in the Proceedings of the Linnaean Society of London for 1858.²

So what happens in fact when there’s too much crowding? Some responses seem to serve a larger purpose. Sibling shark embryos fight to the death in utero. In many nonhuman mammals, brothers and sisters of the same litter compete for access to nipples; often, there is a least competent infant, unsuccessful in elbowing its way to a nipple—the runt of the litter, who becomes progressively weaker with each failed attempt to nurse. The Virginia opossum has thirteen teats and, generally, more than thirteen pups per litter. Only those who regularly get to a teat live. Such competitions weed out the weak. Those species with more teats than pups permit weakling and unaggressive youngsters to reach adulthood. If they are unlikely to compete successfully as adults and pass their genes on, their mother has, from the point of view of her genes, been wasting her time nursing such pups. Those mothers with fewer teats or more pups have a selective advantage. Concern about cruelty and suffering doesn’t, so far as we know, enter into it.

Cities aside, we humans routinely experiment on crowding animals into confined enclosures. The institutions responsible are called zoos; some are much more pernicious than others. A well-known problem of zoos is that many of the inmates are somehow less able to “breed in captivity”; another problem is sustained and violent conflict, usually between males of the same species. Zookeepers have learned that if they wish to maintain their “inventories,” they must often separate the males. Experiments have also been performed in the laboratory to study overcrowding. In all of these cases it’s important to remember the artificiality of the circumstances. An option available in the wild is unachievable in captivity: No matter what the provocation, a caged animal cannot flee conflict and make a new start somewhere else.

Norway rats have been bred in scientific laboratories since the middle nineteenth century. Artificial selection has elicited—partly through unconscious choices by laboratory personnel—a strain of rats that is calmer, tamer, less aggressive, more fertile, and with significantly smaller brains than their wild ancestors. All this is a convenience for those experimenting on rats.³

In a now-classic experiment,⁴ the psychologist John B. Calhoun let Norway rats reproduce in an enclosure of fixed size until the number of occupants, and therefore the population density, was very high. He made sure, however, to provide everyone with enough to eat. What happened?

As the population increased, a range of unusual behavior was noted. Nursing mothers became somehow distracted, rejecting and abandoning their infants, who would wither away and die. Despite the surplus of ordinary food, the bodies of the newborn would be greedily eaten by passersby. An adult female in heat or estrus would be pursued relentlessly, not by one, but by a pack of males. She had no hope of escape, or even sanctuary. Obstetrical and gynecological disorders proliferated, and many females died giving birth, or from complications soon after. When crowded together, the rats lost their inclination or ability to build nests for themselves and their young; their desultory constructions were amateurish and ineffective.

Among the males Calhoun distinguished four types: the dominant, highly aggressive ones who, although “the most normal,” would occasionally go “berserk”; the homosexuals who made sexual advances to adults and juveniles of both sexes (but, significantly, only to nonovulating females): their invitations were generally accepted, or at least tolerated, but they were frequently attacked by the dominant males; a wholly passive population that “moved through the community like somnambulists” with nearly complete social disorientation; and a subgroup Calhoun calls the “probers,” uninvolved in the struggle for status but hyperactive, hypersexual, bisexual, and cannibalistic.

If there were no differences between rats and people, we might conclude that among the consequences of crowding humans into cities—other things being equal—would be more outbreaks of street fighting and domestic violence, child abuse and neglect, soaring infant and maternal mortality, gang rape, psychosis, increased homosexuality and hypersexuality, gay bashing, alienation, social disorientation and rootlessness, and a decline in traditional domestic skills. It’s suggestive, surely. But people are not rats.

Crowding in cats leads to a nightmarish tableau of incessant hissing and squalling, fur standing on end, remorseless fighting, and the designation of pariahs who are attacked by all. But people are not cats either.

Crowding in our nearer relatives, the baboons, can lead to bloodshed and social disorder at least on the scale of rats and cats, as we treat later. In many animals overcrowding also leads to increased susceptibility to disease, and smaller adult stature. But as vervet monkeys become more and more crowded together, the inmates begin studiously avoiding one another, inspecting with great interest the ground on which they sit and the motion of clouds in the sky above. In chimpanzees, crowding does tend to make everybody a little edgy. There is more aggression. But not much more. As the population density increases, chimps make concerted efforts at appeasing one another, at peacemaking.⁵ They have neural machinery and a social idiom to compensate for overcrowding. Are we not more like chimps than like rats?

The rat response to overcrowding, even at its most pathological, might be viewed as making sense in a remorseless evolutionary way. If the population density becomes too high, then mechanisms are set into motion to reduce it. Huge numbers of socially disinterested adults, illness, increased homosexuality, and soaring infant and maternal mortality, all serve this purpose. Eventually, the population crashes, overcrowding is relieved, and the next generation is back to business as usual—until the population pressures build up again. Some of the behavioral responses to high population density in Calhoun’s rats, and in many other species, might be looked on not as barbarous and unfeeling, but as a calamitous necessity, the capability for which has been painstakingly evolved.

We’ve phrased this in terms of group selection, but interpretations in the idiom of kin selection are also possible. We could, instead, have stressed that overcrowding is, almost invariably in Nature, a prelude to famine, so it makes a desperate kind of sense to abandon or eat nursing infants, or to cease building nests for the young, or to arrange that babies be stillborn or not conceived at all.⁶

In many animals—howler monkeys, for example—high population density leads to takeovers by alien males and the wholesale slaughter of resident infants. This behavior is especially vivid in animals where dominant males keep harems or try to prevent other males from reproducing.⁷ But is it fundamentally due to overcrowding, or to the evolutionary strategy of the new dominant male? It benefits the proliferation of his complement of genes to remove all distractions from the females as quickly as possible, move them into ovulation (which killing their young accomplishes), and impregnate them before he’s overthrown by the next usurper.* The more crowding there is, the more challenges from sexual rivals and the more such infanticides. Whether all of the anomalous behavior of Calhoun’s rats can be understood in these ways is still unclear; but surely some of it can.

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If, sympathizing with the rats, cats, and baboons in these experiments, we wished to help them, what could we do? We might be tempted to organize a jailbreak and return them to their natural environments. We would eliminate the overcrowding and—assuming the animals could fend for themselves—hope they would revert to their normal behavior and social organization. But then shouldn’t evolution also have invented mechanisms for dispersing competing organisms so they’re not in each other’s way—especially the most flagrantly aggressive variety, usually the young adult males? This would be to the advantage of both the individual and the species.

In fact, Nature provides such a safety valve: Instead of staying on to fight to the death, the potential losers—those who estimate that they would be vanquished if they continued fighting, or those who judge that the probable benefits of fighting are not worth the risk—may simply pick up and leave. There is an escape clause in their contract, a get-out-of-jail-free card, which precipitously reduces the incidence of mutilation and murder. A few formalities and they’re gone. But lock them up in a zoo or a laboratory apartment house for rats and all possibility of escape is denied them. That’s when they go crazy.

Some kind of mutual repulsion is needed, like that provided by electrical charges of the same sign or polarity. When two electrons are far from one another, they hardly feel each other’s influence. But bring them close together and a powerful force of electrical repulsion is brought into play, the force being stronger the closer together the electrons are. Something similar is true for magnets. Opportunistic animals able, under favorable conditions, to reproduce exponentially need a similar mutual repulsion, increasing quickly as the animals are brought into systematic close contact. There is such a force in Nature: intraspecific aggression, aggression within, internal to, a given species.