Marker

prologue

IN THE WEE HOURS OF February 2, a cold, steady drizzle drenched the concrete spires of New York City, shrouding them in a dense swirl of purplish-pink fog. Save for a few muted sirens, the city that never sleeps was at a relative standstill. Yet at exactly three-seventeen A.M., two nearly simultaneous, unrelated but basically similar, microcosmic events occurred on opposite sides of Central Park that would prove to be fatefully connected. One was on a cellular level, the other on a molecular level. Although the biological consequences of these two events were opposite, the events themselves were destined to cause the perpetrators-all strangers-to violently collide in less than two months.

The cellular event occurred in a moment of intense bliss and involved the forcible injection of slightly more than two hundred and fifty million sperm into a vaginal vault. Like a group of anxious marathoners, the sperm mobilized quickly tapped into their self-contained energy stores, and began a truly Herculean race against death: a remarkably arduous and perilous race that only one could win, relegating the others to short and frustratingly futile lives.

The first task was to penetrate the mucous plug obstructing the collapsed uterine cavity. Despite this formidable barrier, the sperm rapidly triumphed as a group, although it was a Pyrrhic victory. Tens of millions of the initial wave of gametes were lost in a form of self-sacrifice required to release their contained enzymes to make the passage possible for others.

The next ordeal for this horde of minute living entities was to traverse the relatively enormous uterine expanse, almost equivalent in distance and danger to a small fish swimming the length of the Great Barrier Reef. But even this seemingly insurmountable impediment was overcome as a few thousand lucky and robust individual sperm made it to the openings of the two oviducts, leaving behind hundreds of millions of unlucky casualties.

Still, the travail was not over. Once within the undulating folds of the oviducts, the fortunate ones who'd entered the correct tube were now spurred on by the chemotaxis of the descending fluid from a burst ovarian follicle. Somewhere ahead, beyond a tortuous and treacherous twelve centimeters, lay the sperm's Holy Grail, a recently released ovum crowned with a cloud of supporting cumulous cells.

Progressively goaded by the irresistible chemical attraction, a contingent of the male gametes accomplished the ostensibly impossible and closed in on their target. Nearly exhausted from the long swim and from avoiding predatory macrophages who'd engulfed many of their brethren, the number was now less than one hundred and falling rapidly. Neck and neck, the survivors bore down on the hapless haploid egg in a race to the wire.

After an astonishingly short one hour and twenty-five minutes, the winning sperm gave a final desperate beat of his flagellum and collided head-on with the egg's surrounding cumulous cells. Frantically, he burrowed between the cells to bring his caplike acrosome into direct contact with the egg's heavy protein coat to form a bond. At that instant, the race was over. As his last mortal act, the winning sperm then injected his contained nuclear material into the egg to form the male pronucleus.

The other sixteen sperm that had managed to reach the egg seconds behind the winner found themselves unable to adhere to the egg's altered protein coat. With their energy stores exhausted, their flagella soon fell silent. There was no second place, and all the losers were soon swept up, engulfed, and carried off by the deadly maternal macrophages.

Inside the now-fertilized ovum, the female pronucleus and the male pronucleus migrated toward each other. After the dissolution of their envelopes, their nuclear material fused to form the required forty-six chromosomes of a human somatic cell. The ovum had metamorphosed into a zygote. Within twenty-four hours, it divided in a process called cleavage, the first step in a programmed sequence of events that would in twenty days begin to form an embryo. A life had begun.

The nearly simultaneous molecular event also involved a forcible injection. On this occasion a bolus of more than a trillion molecules of a simple salt called potassium chloride dissolved in a shotglass volume of sterile water was injected into a peripheral arm vein. The effect was almost instantaneous. Cells lining the vein experienced a rapid passive diffusion of the potassium ions into their interiors, upsetting their electrostatic charge necessary for life and function. Delicate nerve endings among the cells quickly sent urgent messages of pain to the brain as a warning of imminent catastrophe.

Within seconds, the rest of the potassium ions were streaming through the great veins and into the heart, where they were propelled with each beat out into the vast arterial tree. Although progressive dilution occurred within the plasma, the concentration was still incompatible with cellular function. Of particular concern were the specialized cells of the heart responsible for initiating the heartbeat, those of the brainstem responsible for the urge to breathe, and the nerves and muscle spindles that carried the messages. All were quickly adversely affected. The heart rate rapidly slowed, and the heartbeats grew weaker. Breathing became shallow, and oxygenation inadequate. Moments later, the heart stopped altogether, initiating progressive bodywide cellular death as well as clinical death. A life had been lost. As a final blow, the dying cells leaked their store of potassium into the stagnant circulatory system, effectively masking the original lethal bolus.