On Trails

CHAPTER 2

I RETURNED HOME from Newfoundland with a skull full of new questions. For reasons I couldn’t quite grasp, the fossil trails at Mistaken Point continued to vex me. The more I thought about those inscrutable old scribbles, the more they struck me as curiously inert—and not only because their makers had been dead for half a billion years. Trails tend to possess a certain vital suppleness, a formal litheness or grace, which they altogether lacked.

It was only later, by studying the invisible trails of ants—arguably the world’s greatest trail-makers—that I finally located the glitch: strictly speaking, the Ediacaran trails were not really trails, they were traces. Ant trails gain their magical efficiency from a very simple feedback mechanism: a trail is left behind by one ant and then followed by another, and another, and another, subtly evolving with each subsequent trip. We have no reason to believe that one Ediacaran would have followed in the footsteps (or rather, foot smears) of another. Their trails were a call without a response.

The words we English speakers use to describe lines of movement—­trails, traces, tracks, ways, roads, paths—have grown entangled over the years. I am as guilty of this conflation as anyone else, in part because the meanings of these words, much like the things they denote, tend to overlap. But to better understand how trails function, it helps to momentarily tease them apart. The connotations of trail and path, for example, differ slightly: a “path” sounds dignified, august, and a bit tame, while a “trail” seems unplanned, unkempt, unruly. The Oxford English Dictionary editors define a trail, rather sniffily, as “a rude path.” As they point out, trails only ever pass through wild regions, never cultivated ones; it would sound awkward to speak of strolling down a “garden trail.” But why?

When we take a step back, we find that the key difference between a trail and a path is directional: paths extend forward, whereas trails extend backward. (The importance of this distinction becomes paramount when you consider the prospect of lying down in the path of a charging elephant versus lying down in its trail.) Paths are perceived as being more civilized in part because of their resemblance to other urban architectural projects: They are lines projected forward in space by the intellect and constructed with those noble appendages, the hands. By contrast, trails tend to form in reverse, messily, from the passage of dirty feet.

Over time, the meaning of the two terms converged in North America in the nineteenth century, when Anglos often found themselves traveling almost exclusively on trails left behind by animals and Native Americans. The word acquired its flavor out west; the OED’s earliest citation of “trail”—meaning a footpath, animal trace, or wagon road—dates back to the Lewis and Clark expedition. Colonel Richard Irving Dodge, in 1876’s Plains of the Great West, drew from his tracking experience to give us this helpful definition: trails are a string of “sign” that can be reliably followed. I like this definition, because it gets us away from the erroneous assumption that a trail is synonymous with a strip of bare dirt, but it requires some explanation. “Sign”—a word, like its synonym “spoor,” that is always written in the singular—refers to the marks left behind by an animal in its passing: footprints, droppings, broken branches, tree trunks rubbed bare by antlers. “A trail is made up of ‘sign;’ but ‘sign’ is, by no means, a trail,” Dodge clarified. “Deer make ‘sign,’ but it may be impossible to trail them.” Trails, in this—albeit, somewhat tautological—­formulation, are simply that which can be trailed.

Something miraculous happens when a trail is trailed. The inert line is transformed into a legible sign system, which allows animals to lead one another, as if telepathically, across long distances. (These signs can be physical, chemical, electronic, or theoretical. The medium, in this case, is not the message.)

The truly incredible thing about these sign systems is that they require no special intelligence to create or follow. Some of the animal kingdom’s earliest trail followers were likely marine gastropods (the ancient progenitors of snails and slugs), which emerged during the Ordovician period. Modern-day marine gastropods regularly track one another’s slime trails across the seafloor by tasting the trail’s mucousy surface, a process called “contact chemoreception.” The slime of gastropods primarily speeds their travel, but this slick medium has also evolved into a signaling mechanism, much like how the smooth surface of the highway, as opposed to the bumpiness of the shoulder, signals that a driver hasn’t veered off the road. Certain gastropods, like mud snails, only travel forward on slime trails—following a gradient toward the freshest mucus—which allows them to shadow one another on their herd-like migrations. Limpets, on the other hand, secrete trails that they trace in reverse, groping their way back to the nook-like homes they carve into rocks.

Slime trails function equally well on land, where terrestrial snails and slugs make frequent use of them. Darwin relayed the story of an acquaintance, named Lonsdale, who once placed two Burgundy snails in a “small and ill-provided” garden. The stronger of the two snails climbed over a wall into an adjoining garden where there was more to eat. “Mr. Lonsdale concluded that it had deserted its sickly mate,” Darwin wrote, “but after an absence of twenty-four hours it returned, and apparently communicated the result of its successful exploration, for both then started along the same track and disappeared over the wall.”

Mr. Lonsdale seems not to have considered the possibility that, if the first snail can leave behind an intelligible trail for its mate to follow, no other form of communication is necessary. The trail provides one of the animal kingdom’s most elegant ways to share information. Each inch is a sign, like a scrawled arrow, reading simply:

This way . . .

This way . . .

This way . . .

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The invention of trails provided a powerful new tool of animal communication, a kind of proto-Internet capable of running on a simple binary language—this way and not. No species has exploited this new technology more brilliantly than ants, which routinely use trails to find new sources of food and transport it back to the nest. Scientists now study these tiny, but stunningly efficient, trail systems to learn how to more quickly route bits of information through our own fiber-optic networks.

For many centuries, it was a mystery how ants were able to organize themselves so deftly. Some believed each ant was possessed of a tiny special intelligence, which afforded it rationality, language, and the ability to learn, as the naturalist Jean Pierre Huber argued in 1810. Put simply, this view held that ants found their way to food using their wits, and then “spread the word” of their findings throughout the nest. (This highly anthropomorphized notion remains prevalent among folktales and children’s stories, from Aesop’s Fables to T. H. White’s The Once and Future King. In many of these renditions, like White’s, the worker ants are given their marching orders by an all-­powerful “queen.”) Opponents of this theory, following the teachings of Descartes, held that ants were possessed of no intelligence whatsoever—or, in the language of the time, no “soul”—but were mere machines directed by an almighty deity who either manipulated them like marionettes or engineered them like windup toys. The naturalist Jean-Henri Fabre, an unfashionably late proponent of this theory, wrote in 1879, “Can the insect have acquired its skill gradually, from generation to generation, by a long series of casual experiments, of blind gropings? Can such order be born of chaos; such foresight of hazard; such wisdom of stupidity?” Fabre concluded that it could not. “The more I see and the more I observe, the more does this [divine] Intelligence shine behind the mystery of things.”

On the one side of this debate lie insects blessed with individual wit, on the other, insects cursed with perfect idiocy, but steered by an omniscient hand. It was not until very recently that scientists began to understand that the answer lay somewhere in between: the complex behavior of ants arises not from smart individuals, but from smart systems—a form of wisdom that exists between, as well as inside, living things.

All animals fall somewhere on the spectrum between internalized and externalized intelligence. At one extreme of this spectrum lies the mountain hermit, thoughts swirling about in his lonely head like moths in a bell jar. At the other end lies the slime mold. As sprawling, single-celled blobs, slime molds are about as stupid as an organism can be: they lack even the most basic rudiments of a nervous system. However, they have nevertheless developed a very effective technique to hunt for food: They extend their tentacle-like pseudopods, grope around, and then retract them whenever they come up empty. As they retract, the pseudopods leave behind a trail—or rather, a kind of anti-trail—of slime indicating where food has not been found. Then, continuing their blind search, they head off in a new, slime-free direction. Using roughly this same trial-and-error method, slime molds can solve surprisingly complex problems. When researchers tasked a slime mold with connecting a series of oat clusters mirroring the location of the major population centers surrounding Tokyo, the slime mold effectively re-created the layout of the city’s railway system. Linger a moment over that fact: A single-celled organism can design a railway system just as adroitly as Japan’s top engineers. Whatever intelligence slime molds have, though, is wholly external. When their enclosure is wiped down evenly with slime—effectively erasing their trails—slime molds will begin to wander aimlessly, as if struck with dementia. They don’t retain any information; the trail does.

As a species, humans straddle a line between external and internal intelligence. With big brains and (typically) small clan size, humans have traditionally harnessed individual cleverness to outcompete rivals for food and mates, to hunt and dominate other species, and, eventually, to seize control of the planet. As later chapters will show, we have also externalized our wisdom in the form of trails, oral storytelling, written texts, art, maps, and much more recently, electronic data. Nevertheless, even in the Internet era, we still romanticize the lone genius. Most of us—especially us Americans—like to consider any brilliance we may possess, and the accomplishments that have sprung from it, as being solely our own. In our egotism, we have long remained blind to the communal infrastructure that undergirds our own eureka moments. This egotism extends to our regard for pathways: when we write about trails, we tend to describe them as the creation of a single “trailblazer,” whether it is Daniel Boone blazing the Wilderness Road or Benton MacKaye dreaming up the Appalachian Trail. The reality of how most trails form—collectively, organically, without the need of a designer or a despot—has been increasingly apparent to scientists for centuries, but has remained invisible to most of us for far too long.

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The story of how we grew wise to the wisdom of insect trails begins, oddly enough, with the lowly caterpillar. One spring day in 1738 a young Genevan philosophy student named Charles Bonnet, while walking through the countryside near his family’s home in Thônex, found a small, white, silken nest strung up in the branches of a hawthorn tree. Inside the nest were squirms of newly hatched tent caterpillars, which bristled with fiery red hairs.

At just eighteen years old, frail, asthmatic, myopic, and hard of hearing, Bonnet was a somewhat unlikely naturalist. But he was blessed with patience, attentiveness, and a relentless, burning curiosity. As he approached the cusp of adulthood, his father had begun pressuring him to become a lawyer, but he wanted to spend his life exploring the microcosmos of insects and other tiny creatures, a profession that had scarcely yet been invented.

Bonnet decided to cut down the hawthorn branch and carry it back home. At the time, most naturalists would have sealed the caterpillars in a powder jar, called a poudrier, to better inspect their anatomy. But Bonnet wanted to observe the caterpillars’ natural behavior wholly unobstructed, en plein air, yet from the comfort of his home. He struck upon the idea of mounting the hawthorn branch outside the window frame of his study. That window soon became a kind of antique television, a glass screen displaying a miniaturized world, before which he spent countless rapt hours.

After two days of patiently waiting for signs of life, Bonnet watched the caterpillars emerge from their nest and begin to march in single file up the windowpane. After four hours, the procession had successfully scaled the window; then it turned around. In descending, strangely, the caterpillars followed the exact path they had climbed. Bonnet later wrote that he even traced their route—presumably, with a wax pencil on the windowpane—to see if they ever deviated from it. “But they always followed it, faithfully,” he wrote.

Each day Bonnet watched as the caterpillars mounted exploratory expeditions across the windowpane. Paying closer attention, he noticed that as they crawled, each caterpillar laid down an ultra-fine white thread, which the others followed. Curious, Bonnet rubbed his finger across their trail, breaking the thread. When the leader of the returning party arrived at the rupture, it turned back, apparently confused. The one behind it did the same, and the one behind that. Each subsequent caterpillar plodded calmly along until it reached the gap in the trail, at which point it either turned around or stopped to feel about for the thread, like a man groping for a dropped flashlight. Finally, one of the caterpillars, which Bonnet deemed “hardier than the others,” dared to venture forward: a thread was extended across the void, and the others followed.

Emboldened, Bonnet collected more caterpillar nests, which he placed on his mantel. Soon, scores of caterpillars were exploring his bedroom, meandering across the walls, the floor, even the furniture. Feeling, no doubt, like a small new god, Bonnet found he could control where the caterpillars traveled simply by erasing certain trails. He delighted in showing this trick to visitors. “You see these little caterpillars who walk in such good order?” he would ask. “Well, I bet you that they will not pass beyond this mark”—and he would swipe his finger across their route, stopping them cold.

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Along the southern stretches of the Appalachian Trail, I too sometimes encountered mysterious little white tents in the crotches of trees. Occasionally they grew to monstrous proportions; I would turn a corner to find a tree wholly enveloped in a polygonal cloud. “Mummy trees,” my fellow hikers called them.

For a reason I couldn’t quite place, they gave me the shivers. Tent caterpillars, I would later learn, are essentially creepy animals. Their faces resemble black masks, and their bodies are quilled over in fine, toxin-tipped spines, which can detach and float for more than a mile on a windy day, causing rashes, coughing fits, and pink eye. Some species of tent caterpillar undergo rampant population booms on a ten-year cycle, covering the countryside like spilled oil. In June 1913 a stream of forest tent caterpillars climbed up onto the tracks of the Long Island Rail Road; the rails were soon so thickly slathered with their remains that the wheels of approaching trains spun in place.

A biologist named Emma Despland once told me about the time she walked into a stand of sugar maples during a tent caterpillar outbreak. She described it as a “ghost forest.”

“It’s June and there are no leaves on the trees, and there are these big strands of gunky silk, like Halloween decorations,” she said. “And then you hear this rain falling. Except it’s not rain. It’s caterpillar poop.”

Even among biologists, tent caterpillars are little loved. And yet for centuries, researchers like Despland have been studying them for one reason in particular: as consummate followers—perfectly faithful, perfectly foolish—tent caterpillars represent a reductio ad absurdum of what it means to follow a path. Despland told me that if you were to remove a younger caterpillar from its nest mates, it would spend all its time waving its head around in confusion, looking for a trail, and probably starve to death. Alone, they are utterly hopeless, and yet collectively they can denude entire forests.

Curious to see firsthand how such timorous creatures manage to bind together and thrive in the world, I took the bus to Montreal to visit Despland’s lab, where she studies the forest tent caterpillar. When I arrived she peeled open a Tupperware container to show me the caterpillars: a smattering of fuzzy black critters, like mouse turds come to life. Then, on an old desktop computer in her office, Despland showed me time-lapse video of an experiment she had been conducting to determine how they find food. In the experiment, the caterpillars were placed in the middle of a cardboard runway. On the extreme left end of the cardboard strip was a Quaking Aspen leaf, which caterpillars especially love to eat. On the right was the leaf of a hybrid poplar, Populus trichocarpa × P. deltoides (clone H11-11), which they find unappetizing. The experiment was simple: It was as if a group of blindfolded children were placed in the middle of a long hallway, which held a piece of chocolate cake at one end and a pile of raw celery at the other. Asked to find and share the more delicious item, children could quickly solve the problem by splitting up and calling out to one another. But how would the caterpillars?

Displayed on Despland’s computer monitor were five strips of cardboard, on which five experiments were being conducted simultaneously, but she directed my attention to the second from the bottom, where, over the course of many minutes, a group of caterpillars had mistakenly ventured over to the hybrid poplar leaf. Others followed their trails, and soon the whole nest was crawling on the broad green leaf, though they ate virtually none of it. For an uncomfortably long period of time they failed to correct this initial mistake. They followed their trail back to their “bivouac” (a silken pad, which they construct as a resting place) in the middle of the strip, and then back to the hybrid leaf on the right, but none ventured to the left, where the tasty aspen leaf lay. It seemed each caterpillar would continue to follow the others to the hybrid leaf, leaving more trails, and more feedback, forever.

I recalled a peculiar incident Bonnet had once described witnessing, in which a group of pine processionary caterpillars mistakenly formed a circular trail leading all the way around the rim of a ceramic vase. The details are scant, but it seems they continued marching around and around for at least a whole day. This same phenomenon was later famously observed by Jean-Henri Fabre: to his amazement, the caterpillars walked in circles for more than a week before they finally broke the ouroborosian loop and escaped. In Pilgrim at Tinker Creek, Annie Dillard recounts the horror she felt while reading Fabre’s portrait of these soulless, circling automatons. “It is the fixed that horrifies us,” she wrote. “It is motion without direction, force without power, the aimless procession of caterpillars round the rim of a vase, and I hate it because at any moment I myself might step to that charmed and glistening thread.”

Despland’s caterpillars seemed to be caught in a similarly brainless loop. For more than an hour, the pattern continued: the caterpillars returned to their bivouac, returned to the hybrid leaf, and returned to the bivouac again. I began to squirm.

Eventually, a small contingent broke away and ventured off in the opposite direction. They traveled slowly, with excruciating hesitancy, inching, ducking, cowering, stalling, nudging one another forward, and frequently turning back. Despland guessed that their hesitancy springs from a genetic aversion to ending up away from the pack, alone, where they could get picked off by a bird.

By the end of the second hour, the scouting party had finally made it to the aspen leaf, and others subsequently followed the trail they had blazed. Despite their initial misstep, by hour four all the caterpillars had found the correct leaf and gnawed it to a husk.

The foraging technique of these caterpillars is remarkably simple, even idiotic, but it works. The fail-safe, Despland explained, is that hunger induces restlessness, which eventually compels them to abandon the well-worn trails and go looking for something else. “The leaders tend to be the hungry ones,” she explained. “Because they’re the ones who are willing to pay the cost.”

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One year after his initial caterpillar experiments, Charles Bonnet was outside hunting for a new batch of caterpillars when he happened across a prickly flower called a teasel, whose head harbored a colony of tiny red ants. Ever curious, he plucked the flower, carried it back to his study, and planted it upright in an open powder jar.

One day Bonnet returned to discover that a number of the ants had deserted the nest. Searching about, he found them marching up his wall to nibble the wood at the top of his window frame. In his journal, Bonnet described watching one ant as it climbed down the wall, up the side of the powder jar, and back to the nest. At the same time, two ants emerged from the teasel head and climbed to the top of the window frame, following precisely the same route that the other had just descended.

“Instantly, it came to my mind that these ants which I had in front of me, like the caterpillars, left a trace that directed them in their course,” he recalled.

Of course, he knew that ants did not emit a thread. But they did give off a strong smell, which is sometimes described as being reminiscent of urine. (This odor lent ants their archaic name, “pismires,” and later, “piss-ants.”) The substance, Bonnet theorized, could “more or less adhere to objects they touch, and then act on their sense of smell.” He compared those “invisible traces” with the trails of wildcats, which are imperceptible to humans but plain as blood to dogs.

His suspicion was easily tested: as before, he rubbed his finger across the ants’ pathway. “Doing so, I broke the path on a width equal to that of my finger, and I saw precisely the same spectacle the caterpillars had given me: the ants were diverted, their walk was interrupted, and their confusion amused me for me some time.”

Bonnet had stumbled on an elegant explanation for how ant trails form, which required neither powerful memories, strong eyesight, nor simple language (as Huber and Fabre later proposed). Bonnet theorized, correctly, that ants ordinarily follow trails that lead to their homes and to food sources. However, some ants wander off track, “attracted by certain smells or other sensations to us unknown,” spawning new side roads. If that rogue ant finds food, it will leave a new trail on its return to the nest, and other ants will follow. So, wrote Bonnet, “a single ant can lead a large number of its companions to a certain place without any need of a particular language whereby it announces the discovery that it has just made.”

Judging from his journals, Bonnet seems not to have realized how historic this discovery was. Scientists had long suspected that ants deposit chemicals when they walk; in the sixteenth century, two German botanists, Otto Brunfels and Hieronymus Bock, discovered that ants produce formic acid after noticing that a blue chicory flower, when thrown onto an anthill, turns a vivid red. But no one properly connected the dots until Bonnet.

Around the time of Bonnet’s death in 1793, the zoologist Pierre André Latreille confirmed Bonnet’s suspicion that ants sniff their way through the world. He learned this by amputating the antennae from a number of ants; at once, he wrote, they began wandering aimlessly about, as if in “a state of intoxication or a kind of madness.” Then, in 1891, Sir John Lubbock, the English polymath, performed a groundbreaking series of experiments involving Y-shaped mazes, bridges, and rotating platforms. Through painstaking experimentation, he showed that Lasius niger ants navigate primarily by using scent trails.

In the late 1950s, E. O. Wilson solved the riddle by locating the gland in fire ants that secretes trail pheromones. He had a hunch that the trail substance resided somewhere in an ant’s abdomen, so he split the abdomen open and, using a pair of sharpened watchmaker’s forceps, carefully removed all the organs. Then he smeared each organ across a piece of glass. After each stroke, he checked to see if it had any effect on a nearby colony of ants. Line after line, organ after organ—the poison gland, the hindgut, the little blob of lipids called a “fat body”—prompted no response. Finally he smeared out a tiny, finger-shaped organ called Dufour’s gland. “The response of the ants was explosive,” Wilson later recalled. “As they ran along they swept their antennae from side to side, sampling the molecules evaporating and diffusing through the air. At the end of the trail they milled about in confusion, searching for the reward not there.”

By the year 1960, our fuzzy understanding of ant trails had snapped into sharp focus. Two crucial new terms were born concurrently: a pair of German biologists coined the term pheromone—chemical triggers, or signals—and Pierre-Paul Grassé introduced the notion of “stigmergy.” Stigmergy is a form of indirect communication and leaderless cooperation, using signals deposited in the environment. Termites, for example, organize their massive construction efforts stigmergically: there is no foreman, and no direct communication between the termites. Rather, the termites respond to a series of simple cues in the environment (if dirt here, move dirt there), which in turn impel them to further alter the environment. This behavioral feedback loop can result in structures of stunning efficiency and resilience, like the towering termite mounds of Australia, which, proportional to their makers, are three times taller than our highest skyscrapers. With a combination of pheromones and stigmergy, even the simplest insects could build labyrinthine trail systems.

In the 1970s a biologist named Terrence D. Fitzgerald, being familiar with Wilson’s work, intuited that tent caterpillars might also use trail pheromones. At the time, biologists believed that tent caterpillars followed their nest mates’ silk, which is expelled from their mouthparts, but he had a hunch that they were secreting trail pheromones onto the silk from their back ends, as ants do. So he folded a plain piece of paper in half and ran its edge along the underside of a caterpillar’s abdomen. Then he unfolded the paper and placed some caterpillars on it. Sure enough, the caterpillars marched back and forth along that crease, following the invisible line of pheromones just as Wilson’s fire ants had. (Like Wilson, Fitzgerald was later able to isolate and synthesize these trail pheromones.) This discovery lent a neat symmetry to the path of inquiry Bonnet had started: We learned ants follow pheromone trails by studying tent caterpillars, then we learned tent caterpillars deposit pheromone trails by dissecting ants.

It may seem odd, then, that neither Wilson nor Fitzgerald cites Bonnet’s discovery. In fact, many of Bonnet’s writings, including the story of how he discovered the true nature of ant trails, have never been published in English. Though his career showed a promising start, it ultimately veered off on an ill-fated path. In his twenties, Bonnet became a celebrated naturalist: the first person to witness a virgin birth among plant lice, the first to describe regeneration among worms, the first to learn that caterpillars breathe through holes in their skin, and the first to prove that leaves exhale. Then, in a cruel twist, his vision began to cloud with cataracts. Unable to practice observational science, he turned to more cerebral fields, like philosophy, psychology, metaphysics, and theology. Much of the latter half of his life was spent trying to reconcile the confusing new findings of the biological sciences with his deep religious faith, which held that the world was divinely engineered. Bonnet’s magnum opus—an all-encompassing theory of the universe called the “Great Chain of Being,” which posited that all species were slowly progressing toward a state of perfection over the course of eons—had some influence on later evolutionary theorists like Jean-Baptiste Lamarck and Georges Cuvier. But in the broader span of scientific progress, it proved little more than a theoretical side road, which was later made obsolete by Darwin’s theory of evolution by natural selection. By the end of his life, Bonnet’s blindness caused him to suffer from phantasmagoric visual hallucinations, which are now known as Charles Bonnet syndrome.I Today, that syndrome is primarily what he is remembered for, when he is remembered at all.

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Every trail tells a story, but some trails tell it more eloquently than others. The trails of Despland’s forest tent caterpillars, for example, are blunt—they are essentially able to shout just one phrase: This way! The trails of certain ant species are more sophisticated: they can whisper as well as shout. The strength of the chemical trail tells the colony how desirable the trail’s destination is, which allows for more nuanced communication and nimbler collective decision making. Scientists have long pondered how ants, which are individually quite stupid, can behave so intelligently as a colony. “The reason is,” E. O. Wilson once wrote, “that much of the ‘spirit of the hive’ is actually invisible—a complex of chemical signals we have only now begun to reveal.”

Consider the fire ant: Once a scout has found a food source, excited by its discovery, on its return trip it presses its stinger to the ground to release a stream of pheromone, like ink from a fountain pen. The more food it finds, the more pheromone it deposits.II Other ants follow this trail to the food, and then they lay more trails home. So if there is a large store of food, the trail will emerge quickly and blaze bright (chemically speaking), which will attract more ants. Then as long as food remains, the trail will continue to draw more ants. But once the food runs out, the trail evaporates, and the ants gradually abandon it for another, stronger trail. This process neatly illustrates how stigmergy allows simple beings to arrive at elegant solutions to complex problems all on their own.

The basic mechanism at work here is the feedback loop: cause leads to effect (an ant finds food, and deposits a trail as it returns to the nest), then that effect becomes a new cause (that trail attracts more ants), which then leads to an amplified effect (they lay down their own trails, recruiting more ants), ad infinitum. Feedback loops can be divided into two types: the desirable kind, known as a virtuous circle, such as when ants leave stronger and stronger trails to a food source; or the undesirable kind, called a vicious circle, like when a microphone is placed too close to an electronic amplifier, which allows minor sounds to self-amplify into those terrible, high-pitched shrieks familiar to any concertgoer. (Scientists used to poetically refer to the latter phenomenon as a “singing condition”; today, we simply call it feedback.)

In the circling of tent caterpillars Bonnet and Fabre both witnessed, in a strikingly literal form, how the same mechanism that gives rise to a virtuous circle can also give rise to a vicious one. The animal psychologist T. C. Schneirla witnessed this grim transformation in 1936, while working at a laboratory on an island in the middle of the Panama Canal. One morning, the resident cook, Rosa, approached Schneirla in a state of feverish excitement. She led him outside, where he found, on the cement walkway in front of the library, hundreds of army ants marching in a circle about four inches across.

Army ants, which are blind, rely heavily on pheromone trails to navigate the world. Most of the time, they march in thick raiding columns, consuming everything in their path, a habit that has garnered them the nickname “the Huns and Tartars of the insect world.” Schneirla could tell that something had clearly gone wrong with this colony. Instead of a marching column, the swarming mass resembled a ragged vinyl record, with concentric black rings spinning frantically around a hollow center. The circle widened as the day wore on. In the afternoon, rain began to drum the pavement, which divided the mass of ants into two smaller vortices, each rotating until nightfall. The next morning, Schneirla awoke to find that most of the ants had died; those that remained continued to plod in slow, tragic circles. A few hours later, all were dead, and other species of scavenging ants had arrived to carry them away.

Schneirla was careful to point out that the doomed loop had most likely formed because the ants were walking on perfectly flat cement; otherwise, the undulations of the jungle floor might have disrupted it. However, looping trails had been recorded under different conditions by other prominent scientists, like the entomologist William Morton Wheeler, who once watched a group of ants circle the base of a glass jar for forty-six hours. (“I have never seen a more astonishing exhibition of the limitations of instinct,” he wrote.)

In 1921 the explorer-naturalist William Beebe described running across a colony of army ants marching in an enormous circle through the Guyanese jungle. Beebe followed the procession for a quarter mile, under buildings and over logs, only to find that their trail ended where it began. Astounded, he traced the crooked circle again and again. The procession continued to circumambulate for at least a full day, “tired, hopeless, bewildered, idiotic and thoughtless to the last.” By the time that a few stragglers at last broke from it and wandered away, most had fallen dead from starvation, dehydration, or exhaustion.

“This peculiar calamity may be described as tragic in the classic meaning of the Greek drama,” wrote Schneirla. “It arises, like Nemesis, out of the very aspects of the ant’s nature which most plainly characterize its otherwise successful behavior.”

Beebe was more succinct. “The masters of the jungle,” he wrote, “had become their own mental prey.”

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There is a simple reason why we find the image of circling ants or caterpillars so troubling. The first instinct of humans who are lost in the wilderness is to cling to any trail they find and never leave it. Indeed, authorities on wilderness survival commonly recommend this tactic: “When you find a trail stay on it,” declares a backpacking guide published by the U.S. Forest Service, in a section titled “If You Get Lost.” A trail, the naturalist Ernest Ingersoll once wrote, is a “happy promise to the anxious heart that you are going somewhere, and are not aimlessly wandering in a circle.” A circular trail, then, is a cruel trick, a breach of logic, almost a kind of black magic.

A few years ago, my partner and I moved from a small apartment in New York City to a small cabin in British Columbia. Behind our property stands a tall cedar forest, and behind that lie the cold green waters of the Georgia Strait. The cabin often startles visitors when they first see it. Our next-door neighbor, Johnny, a classical guitarist, built it in a fit of modernist whimsy; it looks like two railroad cars stacked one atop the other. The ground floor is made of polished concrete, and the windows are almost the size of the walls. The insulation is scant, the electricity is always cutting out, the garden is plagued with deer, and the nearest supermarket is a twenty-five-minute drive away, but it’s quiet and the air is clean and there are plenty of walking trails nearby.

At the end of our dirt road, where it joins a bend in the main thoroughfare like a needle in the crook of an arm, there is a little trail leading off into the woods. Johnny informed us that it led to a place the locals call the Grassy Knoll: a soft green tuft atop a rock outcropping over the strait. It’s a lovely perch, they say, to watch the sun set over the mountains of Vancouver Island. However, Johnny strongly advised us against staying that long, for fear we might get lost. “Even I get turned around in there,” he said, “and I’ve lived here for twenty years.” Another neighbor, Corey, told us that he’d once gotten lost while walking in the forest with his infant daughter. When the sun began to set, he felt the first electric touch of panic, an early sign of what psychologists call “woods shock,” or what used to be called simply “bewilderment.” He kept his wits and got out, but as he recounted the story one night around a campfire, I could see the feeling seep up, blackly, behind his eyes.

Remi and I were not worried. It was just a little provincial park, after all, only five hundred acres. If lost, one need only walk three miles in any direction to hit either the coast or a road. Setting off at about three o’clock, we walked down to the end of our street and ducked through the dark curtain of branches.

On the other side, the light clouded to the opacity of sea glass. We looked around, blinking, at a temple of riotous decay, evergreen, shade-blue. On the coasts of British Columbia, the prodigious rainfall, sunny summers, and rich soil thrust the trees upward; the taller ones shed their lower branches like the vestigia of a rocket ship. But eventually that which nourishes, topples. The trees fall to the ground quietly, with a huff, and there turn to moist brown crumbs. Everything, everywhere, is furred with moss and bearded with lichen. Slip on a wet root and you will fall, weirdly slowly, through the gray-green air, and the ground will rise up to receive you in its soft heft.

The trail wasn’t built by the park service—some local do-gooders had apparently cleared it—which meant that it was less legible than it might otherwise be. The only trail markings were the occasional ribbon tied to a branch where the trail skirted a swamp. The paths tended to split and splice. Johnny had given us directions for finding the knoll: turn right at the first T-shaped fork in the path and keep left until you reach the shore. It seemed simple enough.

When we reached the first fork in the trail, Remi propped a stick up against a tree so we would have a point of reference in case we got lost. We turned right and followed the trail around in a wide arc, chatting happily, until we found ourselves standing at a fork in the path. There, off to the side, was the stick Remi had propped up against the tree. We had gone in a circle. Befuddled, we turned around and set off in the opposite direction this time, and, minutes later, found ourselves back at the stick again.

In Roughing It, Mark Twain recalls heading out into a snowstorm, bound for Carson City. A man named Ollendorff, bragging that his instinct was as sure as any compass, promised to lead the group. After half an hour of plodding through the snow on horseback, the men came upon fresh hoof-tracks in the snow. “I knew I was as dead certain as a compass, boys!” shouted Ollendorff. “Here we are, right in somebody’s tracks that will hunt the way for us without any trouble.”

The men began to trot along the tracks. Before long it became evident that they were gaining on whoever was up ahead, because the tracks grew more distinct.

We hurried along, and at the end of an hour the tracks looked still newer and fresher—but what surprised us was that the number of travelers in advance of us seemed to steadily increase. We wondered how so large a party came to be traveling at such a time and in such a solitude. Somebody suggested that it must be a company of soldiers from the fort, and so we accepted that solution and jogged along a little faster still, for they could not be far off now. But the tracks still multiplied, and we began to think the platoon of soldiers was miraculously expanding into a regiment—Ballou said they had already increased to five hundred! Presently he stopped his horse and said:

“Boys, these are our own tracks, and we’ve actually been circussing round and round in a circle for more than two hours out here in this blind desert!”

It has been thought for centuries that human beings have a natural tendency to walk in circles. In 1928, a biologist named Asa Schaeffer claimed to have shown experimentally that blindfolded people walk, run, swim, row, and drive automobiles in spiraling patterns, a phenomenon he attributed to a “spiral mechanism” in the brain. The navigator Harold Gatty believed that people circled because of simple biological asymmetry; one leg tends to be longer or stronger than the other. (“With regard to our anatomy,” he wrote, “we are all of us unbalanced.”) In 1896, the Norwegian biologist F. O. Guldberg argued that circling was one of the “general laws” of biology. He recounted stories of birds wheeling in front of lighthouses, schools of fish whirling in the lamps of deep-sea divers, hares and foxes circling to escape hunters, and men lost in fog wandering in loops.

Guldberg didn’t see circling as a form of error. The law of circular movement, he argued, assures that lost animals will always be able to find their way back to “the native place to which animals in the struggle for existence must so often return, be it the udder of the cow, the warmth-giving wings and the guiding experience of the hen, or the sheltering tree or bush chosen by maternal instinct.” Whether we like it or not, he argued, we circle to find our way back to familiar ground.

In 2009, a researcher named Jan Souman decided to test the circling instinct. He equipped volunteers with GPS tracking devices and instructed them to walk in a straight line across unfamiliar terrain, both in the forests of Germany and the deserts of Tunisia. Without the aid of directional cues, like the sun, the subjects did tend to circle back on their own trails; that much is true. “It seems easy to walk in a straight line,” Souman told me. “But if you think about it, it’s actually not that easy at all.” Like riding a bicycle, walking a straight line is in fact a complex neural balancing act, which is what makes it an effective test of whether a person has had too much to drink.

Further experiments ruled out leg length and leg strength as factors. Souman also found no evidence to support the assumption that there is a “circling instinct” in the brain. The paths his subjects took were not big circles or spirals, but rather something more like the random squiggles a toddler makes with a crayon. At times, they looped back on themselves—the point at which walkers typically spot a familiar landmark, falsely conclude that they are walking in a circle, and begin to panic—but walkers almost never circled all the way back to the start. Souman concluded that on average people who are lost, without external navigational cues, will typically not travel farther than one hundred meters from their starting point, regardless of how long they walk.

A horrifying thought: On a cloudy day, in tall woods, with no other cues and no compass, a person will not travel more than the length of a football field in any one direction.

Remi and I were in just such a situation. The sky was dull pewter. Everything was covered equally in moss, so that old trick wouldn’t be of any help. We hadn’t brought a compass, as Johnny had advised. I did have my phone, which had a digital compass, but the one time I ever needed it, the needle spun limply, like a wandering eye. We were cut off from every form of external reference, except the trail. At one point we grew so frustrated in our circling that we struck off, bushwhacking in the direction we guessed the water must be, but we soon became nervous about getting lost, so we dutifully returned to the charmed thread.

At last, as the sky was darkening, one of us realized there were in fact two forks in the trail that looked identical, because some other hiker had previously propped up another stick against a tree in precisely the same fashion we had. Remi kicked the stick into the woods and the spell was broken. The next turn at the fork took us directly home.

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According to Guldberg, Norwegian country folk refer to the act of walking in circles as “approaching on a false scent.” The phrase—which must be somewhat rare, because the Norwegians I’ve spoken to have never heard it—wonderfully evokes the illusory sense of progress that attends the circling walker. Circular arguments function in much the same way: One side feels that an intellectual victory is just within reach, as does the other side. Both sides launch attacks and counterattacks and counter-counterattacks, but neither can win a decisive victory, and so the two continue “circussing round and round,” like a pair of rats chasing one another around the outer rim of a barrel.

Until the latter half of the last century, ant researchers generally fell into one of two camps: they either believed ants were sentient beings, capable of learning, or they believed they were instinctive machines. As explanations based on God’s role as a “prime mover” fell out of fashion in the nineteenth century and evidence of ants’ problem-solving abilities continued to mount, the proponents of sentience appeared to be gaining ground. But then, beginning in the 1930s, Konrad Lorenz, the father of a new field of science called ethology, injected new life into the mechanistic argument by showing how insects rely upon “fixed action patterns”—what, in a prior era, would have simply been called “instincts”—which were genetically coded, rather than divinely ordained. God was swapped out, and genetics was swapped in, but the basic argument remained the same. At its heart, the debate revolved around a central paradox: If ants are intelligent, then why do individual ants behave so stupidly? But then, if ants are empty-headed, how can their colonies solve such a wide array of complex problems so brilliantly?

It was not until the advent of computing that this circle was finally broken; early computers opened up a new path forward. By programming computers to perform insect-like tasks, and by studying the (previously, overwhelmingly complex) behavior of swarms using computers, we began to understand that simple machines following a simple set of rules can ultimately make highly intelligent decisions. They are not either simple or smart; they’re both.

Regular conferences in the new field of “cybernetics”—the study of automated systems—were held throughout the late 1940s and early 1950s, where biologists and computer scientists began discussing the considerable overlap between their fields. At the second meeting, Schneirla gave a lecture on how he had trained a common black ant to navigate a maze—being careful to regularly swap out the paper linings on the floor, so that trails couldn’t accumulate—which proved that some ants could memorize basic routes. This finding suggested that individual ants had more powerful brains than many scientists had previously suggested. However, this proposition was later undercut when another attendee, Claude Shannon—famous for quantifying information into “bits”—successfully built a robotic ant, with a processor that was ten times simpler than even the most rudimentary pocket calculator. An electronic “antenna” on wheels, the robo-ant explored mazes following a simple trial-and-error program, bumping up against the walls until the antenna touched its “goal” (a button that shut off the robot’s motor). On the second run-through, having memorized the maze, the robo-ant was able to complete it without touching any of the walls.

The roboticization of the insect world has continued steadily ever since. A few years ago, a researcher named Simon Garnier built robotic ants that could follow electronic pheromone trails. The trails were laid down by a row of overhead projectors, which automatically tracked each robo-ant’s movement; meanwhile, light sensors were installed in each robo-ant’s “head,” so it could follow the other robo-ants’ glowing trails. Essentially, by following just two simple rules—explore randomly until you find either a “trail” or “food,” and follow the strongest trail you find—the robo-ants were ultimately able to find the shortest route through a maze.

The shift toward studying ant colonies as robotic rule-followers was mirrored by a growing sense that an ant colony could function as a single, self-organizing system, much as a computer is a collection of individual circuits. This idea was famously demonstrated in the 1970s by a Belgian researcher named Jean-Louis Deneubourg. One of his most famous experiments involved connecting a nest of Argentine ants and a food source with two different bridges. The two bridges were alike in all respects, except that one bridge was twice as long as the other. In the beginning, the ants chose between the two bridges randomly, but over time, the colony overwhelmingly chose the shorter bridge, for the simple fact that their pheromones accumulated there more quickly. The ants’ system was neatly self-­regulating—the shorter the path, the fresher the pheromones, and the more traffic it attracts. Here was the key: Ants may be individually stupid, but they have a high level of what Deneubourg calls “collective intelligence.”

By regarding ant colonies as intelligent systems composed of individuals following simple rules, Deneubourg was able to make another leap forward: He found that he could describe their movements with mathematical formulas, which could then be used to create computer models. Ant colony algorithms—in which myriad initial routes are explored, the best ones being amplified while the others fade—have since been used to improve British telecommunications networks, to design more efficient shipping routes, to sort financial data, to better deliver supplies during disaster relief operations, and to schedule tasks in a factory. Scientists chose to model their algorithms after ants (as opposed to, say, tent caterpillars) because ants are constantly tweaking their designs and probing for new solutions; they tend to find not only the most efficient solution, but also a slew of effective backup plans.

I spoke with Deneubourg one winter morning at his home in Brussels. He greeted me at the door: a compact, spritely, gray-haired man with big ears and a wide smile. If wrinkles are a graph of all past expressions, his pointed decidedly gleeward.

From the outset of his career, when he studied under the famed systems theorist Ilya Prigogine, Deneubourg had sought to reveal the invisible systems that underlie animal behavior. He realized early on that collective intelligence extends well beyond insect colonies: indeed, historically the notion referred first to humans, and only much later to insects. The term “collective intelligence” appears as early as the 1840s, when the democracy activist Giuseppe Mazzini used it to critique Thomas Carlyle’s belief that history was nothing more than the record of the actions of “Great Men.” Mazzini argued that the greater goal of history was to discern the “collective thought . . . in the social organism”; for too long, he wrote, historians had focused on the petals rather than the whole flower. A fervent Catholic, he believed that the “collective intelligence” of humans ultimately stemmed from an almighty God, of whom humans were mere “instruments.”

Deneubourg sought to dispense with divine explanations and instead show how collective intelligence can emerge (among insects and people) from the interactions of individuals. In one early paper he argued that people tend to build their settlements stigmergically, just like ants: they unconsciously modify the environment, which sends a signal instructing other people how and where to build. For example, if you build a home in an unpopulated area, other people may start to perceive that area as a nice place to build a home; build enough homes and someone may build a shop; build enough shops and someone may build a factory or a shipping port. No top-down oversight is necessary; cities can arise from the ground up.

The week before I met Deneubourg, I had talked with one of his disciples, a professor in Toulouse named Guy Theraulaz, who showed me a video of how Messor sancta ants dig a network of branching tunnels in a disc of dirt. Next, he showed me aerial photographs of unplanned cities—villes spontanées—like Benares, Goslar, and Homs. The similarity was striking. He and his colleagues had found that both these systems found a near-optimal mathematical balance between efficiency (a minimum of paths) and robustness (the good kind of redundancy, whereby the collapse of a single avenue does not lead to a systematic collapse).

“The interesting thing is that in Rome, originally that was a grid system,” he said. “The whole system was destroyed by time, and then it converged into a medieval organic system.” Likewise, many cities across Europe that were built on the Roman grid—Damascus, Mérida, Caerleon, Trier, Aosta, Barcelona—later collapsed back into an organic layout, as people began taking shortcuts across empty quadrants, filling in extravagant plazas, and altering the imperial road network to their needs. Left to their own devices, people unwittingly redesigned their cities precisely as ants would.

Sitting in Deneubourg’s office, I thought back to this experiment. I wondered how a veteran collective intelligence researcher, knowing what he knows, would use that knowledge to design a better city. So I asked Deneubourg: If he were the mayor of a new city being built ex nihilo, like Brasília, how would he organize it?

“I would like to see the emergence of the town,” he said. “If I was the mayor—and the probability of that happening is quite low—my attitude would be very liberal. My objective would be to offer different types of material to help the citizens find the solution that they prefer.”

I found this answer somewhat surprising. By all accounts, he was an expert in the design of efficient systems. And yet he would withhold his expertise and allow the town’s residents to plan their own town?

“Yes,” he replied, with a look of impish mirth. “To believe that you have the solution for another person is a form of stupidity.”

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As the human population continues to swell and gather in ever more densely crowded, hive-like cities, the collective intelligence of ants begins to look all the more astonishing by comparison. Much of ants’ inventiveness arises from their almost utopically (or dystopically, depending on your outlook) high degree of selflessness, which we notably lack. For example, when traversing a V-shaped ramp in a lab, army ants will construct a bridge out of their own bodies to create a shortcut across the crook. In human terms, this would be as if a businessman, while rushing off to work, decided to speed the passage of his fellow commuters by laying his body down over a gap in the sidewalk. I do not foresee us developing this kind of altruism any time in the near future. Nevertheless, there are many lessons humans can glean from the wisdom of ants.

When walking among large crowds, for example, both humans and ants naturally form lanes of traffic. However, among human crowds, those lanes break up and then slow down to reformulate every thirty seconds or so, whereas ant lanes remain in a constant, steady, orderly flow. To find out why, a crowd theorist named Mehdi Moussaid set up video cameras on balconies overlooking some of the busiest pedestrian areas in the French city of Toulouse. What he found was that a single impatient person tends to weave through the crowd, disrupting the smooth flow and slowing everyone else down. (When Moussaid told me this, I laughed in uncomfortable recognition. While commuting across Manhattan to my old job, I saw this phenomenon every morning in the crowded subway tunnel between Sixth and Seventh Avenues. Perpetually late for work, I usually was that jerk.) Ultimately, moving with the flow, rather than racing through it, gets everyone in the swarm to their various destinations more quickly.

In another surprising study on ant traffic dynamics, a former colleague of Moussaid’s named Audrey Dussutour showed that ants never get stuck in traffic jams. One advantage ants have is that their highways have flexible boundaries, so they are able to effortlessly widen them as traffic increases. Even in artificially constricted conditions, however, ants still adapt better than we do. Dussutour proved this by pouring Argentine ants into a basic bottleneck-shaped maze; from above, the ants resembled a dense crowd of people trying to exit a theater through a narrow set of doors. But no matter how many ants she poured into the bottleneck, she could not induce them to grind to a halt the way people inevitably would.

She told me she had recently stumbled upon a likely explanation: She had noticed that when the crowd reaches a certain density, a small number of ants—about ten percent—will stop cold in the middle of the flow, “like stones.” Remaining frozen for up to twenty minutes, the stationary ants split those moving around them into lanes, which prevents jams. By slowing down, certain self-sacrificing individuals allow the colony to move faster. This finding meshes with similar research on human crowds, which has shown that placing an obstacle like a pillar directly in front of a doorway will cleave crowds into neat rows and quicken their flow.

Talking with Dussutour, I began to envision a future where swarms of driverless cars would use ant-based algorithms to forever eradicate traffic jams. In the past, such techno-utopic schemes had always seemed far-fetched to me, because I imagined the cars would require a centralized supercomputer to coordinate their movements. (Think of the hellacious traffic jams that would ensue if that supercomputer were to malfunction.) But a growing body of research—especially in the nascent field of swarm robotics—has proven the cars could effectively coordinate themselves without a godlike hand steering them; highly sophisticated coordination can arise from the bottom up, through individual machines following simple rules.

However, Dussutour stressed that it would be a mistake to think that just because ants behave selflessly and cooperatively, they are all identical and predictable, like robots. Her work has led her to believe that the next big paradigm shift in collective intelligence research will stem from the realization that there are notable individual differences between members of a swarm. “People always say ants are the same,” she said. “Bullshit.” For example, she noted, researchers have found that fourteen percent of common black garden ants never lay a trail during their various foraging trips. Another study found that at least ten percent of foraging green-headed ants will eat whatever they find without ever bringing anything back to the nest. A third study found that as many as twenty-five percent of Temnothorax rugatulus do no work at all. No one knows why these selfish ants exist—whether they provide some hidden evolutionary advantage to the colony, or whether they merely demonstrate that no species is without its share of rebels and slackers.III

Systems built on universal trust are universally easy to exploit. This is why, among humans, members of utopian communes must expend an enormous amount of energy policing against shirkers and charlatans. (“Communes,” wrote the social psychologist Jonathan Haidt, “can survive only to the extent that they can bind a group together, suppress self-interest, and solve the free rider problem.”) Because of the premium placed on social cohesion, cooperative communities—­from hives to nations—are also prone to being swayed by charismatic leaders. Experiments among shoals of golden shiner fish have shown that a single emphatic individual can alter the trajectory of an entire school of fish regardless of whether it is in the best interest of the group. Likewise, it has been found that among humans, the most confident, talkative member of a group often becomes the group’s leader, more or less regardless of the quality of his or her input (a phenomenon called the “babble effect”).

“The wisdom of crowds doesn’t work all the time,” said Simon Garnier, who runs a research laboratory at the New Jersey Institute of Technology called the Swarm Lab. “If you play it right, you can make crowds go wherever you want.”

Garnier was referring to the 2004 book The Wisdom of Crowds, by James Surowiecki, which described the ways that crowds of perfectly average people can collectively make judgments that rival those of the most highly regarded experts. The canonical example of this phenomenon is an experiment run by the British scientist Francis Galton. In 1906, Galton collected data from a group of people at a country fair who were trying to guess the weight of a fat ox. Of the roughly eight hundred people who wagered a guess, most were wide of the mark. However, the average of all their guesses was nearly perfect.

This experiment would later be repeated many times. Oddly, researchers learned that the key to the experiment was that each person needed to judge the weight of the ox independently, without sharing their guesses with one another. In similar experiments where people were given access to one another’s answers, the collective intelligence of the group worsened. Often, the early guesses provoked a false consensus to form, a vicious circle that caused the later guesses to hurtle toward ever-greater error. “The more influence a group’s members exert on each other,” wrote Surowiecki, “the less likely it is that the group’s decisions will be wise ones.”

I was startled when I first read this finding, because it appeared to contradict everything scientists have learned over the past three hundred years about how trails form. When trails are taking shape, every member of a crowd has access to every previous walker’s guess, because their choices are written right there in the dirt. And yet trails nevertheless tend to find optimal routes across the landscape, rather than veering off on wild, mistaken detours. How could this be?

I recently ran across an answer in a paper by a bioscientist named Andrew J. King, who conducted a clever update on the famous Galton ox-weighing experiment. In it, he asked a group of 429 people to guess the number of sweets in a jar. But this time, he made a few tweaks: He gave each member of one group access to the guess of the previous guesser. He gave another group the mean of all previous guesses. And he gave the members of a third group access to a random previous guess. All these pieces of additional information, as predicted, skewed the group’s answers for the worse. However, when he gave members of a fourth group access to the “current best guess”—the previous guess which was currently closest to the mark—he found that that group not only outperformed the three others, but in certain respects it also outperformed the classic Galtonian, private-information-only group.IV Among crowds, sharing more pieces of random information is generally unhelpful—like rumors swirling through a school, they amplify toward ever-greater falsehood as they go. But more reliable information—even if it is not perfectly correct—kicks off a process of fine-tuning, until the answer is revealed.

Every trail is, in essence, a best guess: An ant does not leave a strong pheromone trail unless it has found food, which means that it has already made a correct calculation of where the food is. The same rule applies to humans—we generally don’t make trails unless there is something on the other end worth reaching. It’s only once an initial best guess is made, and others follow it, that a trace begins to evolve into a trail.

As Huxley argued, the same pattern underlies all scientific progress; best guesses are ventured, which, over time, become better guesses. Thus a trail grows—a hunch is strengthened to a claim, a claim splits into a dialogue, a dialogue frays into a debate, a debate swells into a chorus, and a chorus rises, full, now, of clashes and echoes and weird new harmonies, with each new voice calling out:

This way . . .

This way . . .

This way . . .

I. Oddly enough, Charles Bonnet syndrome is so named not because Bonnet suffered from it, but because he was the first person to describe it: his grandfather, Charles Lullin, had suffered from it decades earlier, and Bonnet wrote a case study about him. The fact that Bonnet later acquired the syndrome as well was merely an unhappy coincidence.

II. Much of the apparent stupidity of forest tent caterpillars stems from their lack of this seemingly simple, but quite ingenious, innovation.

III. Meanwhile, researchers have also continued to discover the extent of diversity between different species of ants. Additional varieties of trail pheromone have been discovered, including a not-this-way signal. And certain species of ants, it’s been found, have even evolved entirely different ways of navigating, particularly in places like Arizona or Australia, where a hot, dry climate causes trail pheromones to evaporate too quickly. In these regions, ants have been found to navigate using a variety of cues, including the angle of the sun, the direction of the wind, and the texture and slope of the ground. One species of desert-dwelling ant has even been found to “count” its steps, which allows it to navigate using dead-reckoning.

IV. The private-information-only group was closer in regards to the median, but the current-best-guess group was closer in regards to its mean. On the whole, both were much closer than the other three groups.