Dr. Schaffer calls that balance “the trade-off function.” The particular trade-off at issue is between present and future—that is, the immediate prospect of producing offspring versus the chance of surviving to produce other broods later. An underlying premise here is that an animal or a plant has, at each stage in its life, only a limited total amount of available energy that it can spend on the business of living. That limited energy must be shared out among three fundamental categories of effort—routine metabolism, growth, and reproduction—and an optimal life history is one that balances the shares most efficiently to produce evolutionary success. Evolutionary success, of course, is measured on one simple scale: How many offspring does the creature leave behind? All this is quite basic.
Schaffer’s trade-off equation merely codifies that crucial balance between present and future, between short-term and long-term concerns, between effort devoted to immediate self-preservation and effort devoted to parenthood. His Bi represents the reproductive potential of a given creature right now. The factor pi stands for the probability (or improbability) that the given creature, having bred once, will survive to breed again later. The parenthesis (vi+1/v0) will be the remaining reproductive potential that an experienced parent can expect still to possess at that hypothetical later time. Balance all these considerations against one another, with just the proper commitment of energy (at each age) to metabolism, to growth, to reproduction, and the result is high evolutionary success. This is the burden of
Now let’s try it in English. If a female Chinook salmon, having swum 2,000 miles up the Yukon River, having climbed rapids and dodged otters and leapt cascades, having beaten her fins to tatters digging a gravel nest and fought off other salmon to keep the spot inviolate—if this poor haggard creature has virtually no chance of surviving to accomplish the same entire feat again, then she will be required by the forces of natural selection to sacrifice herself totally, in one great suicidal effort of unstinting motherhood from which she cannot possibly recover. She will lay about five thousand eggs. And then she will croak.
Likewise for those Sonoran agaves, for those Chinese bamboos. The terms of the trade-off are the same, the results are the same, only the numbers and the details are different. Bamboos seem to sacrifice themselves for the sake of predator satiation—that is, producing so many seeds that after all the rats and jungle fowl of China have eaten their fill, a few seeds will still be left to germinate. The agaves compete with each other to produce taller and yet taller flowers, apparently because their pollinators deign to visit only the tallest. The evolutionary consequence in each case, as with salmon, is semelparity.
But Dr. Schaffer’s neat mathematical model is not without gaps, not without weaknesses. What about the Atlantic salmon, for instance, which faces an almost identical set of circumstances to those the Pacific species do yet which doesn’t resort to semelparity? It can be argued that Schaffer’s equations constitute an unduly abstract version of reality. To some observers, such airy theorizing has little more connection to the untidy actualities of ecological fieldwork than it does to, say, metaphysical poetry.
At Christmas of the year 1600, John Donne secretly married a young girl named Anne More, a gentle but dignified sixteen-year-old whose hotheaded father was a powerful nobleman, serving as Queen Elizabeth’s Lieutenant of the Tower. Donne himself was twenty-seven and employed as private secretary to the girl’s uncle. It was a reckless move, this marriage, putting passion before prudence, and Donne knew that. He suffered consequences: dismissed from his job, briefly imprisoned, denied the dowry that Anne otherwise would have brought, and left to struggle for years on the margins of poverty with his adored wife and their many children. Around that time he wrote:
Love with excesse of heat, more yong than old,
Death kills with too much cold…
Once I lov’d and dy’d; and am now become
Mine Epitaph and Tombe.
Here dead men speake their last, and so do I;
Love-slaine, loe, here I lye.
It’s highly unlikely that John Donne ever set eyes upon a Pacific salmon, or a Sonoran agave, or even a transplanted grove of Phyllostachys bambusoides in some London botanical garden. But we can safely assume that he would have understood.
A Deathly Chill
DEATH IS PERSONAL. It’s sealed over by subjectivity and silence; one of those things either you do or you talk about, but not both. Notwithstanding the work of Elisabeth Kübler-Ross, it is the single inevitable human enterprise that we can have no hope of comprehending in advance. The contemplation of death is, after all, something live people engage in, by way of linguistic bamboozlement and philosophical placation of themselves. I repeat all this obvious stuff here because of the Ram Patrol of Chattaroy, Washington, and the question of hypothermia.
On August 10, 1982, an Associated Press item ran in a corner of the back page of my local newspaper under the headline “Hypothermia Blamed in Deaths of Scouts.” The story was bizarre and pathetic. Four young Boy Scouts and two adult leaders had been found drifting, dead, in a cove of a glacier-fed Canadian lake near the west border of Banff National Park. They were stragglers from a canoe trip that had included twenty-three other boys and men, and they had been missing since just the previous afternoon. When discovered, all of the corpses were floating, head up and neatly strapped into lifejackets, not far from their undamaged canoes. There was no sign of accident, desperate struggle, or panic. One of the two adults was still wearing his glasses and hat. “They were in the Ram Patrol, our most experienced group,” a scoutmaster told the AP. “We had them follow the others because they were the best.” The water temperature was steady at around 45°F, and all of the scouts had been in and out of it, swimming and bathing, for the whole week. The presumed cause of death was hypothermia.
It would not be quite accurate to say that the four boys and two men of the Ram Patrol had frozen to death—not at 45 degrees Fahrenheit. Rather, evidently, they had been chilled to death. “It was like they had just gone to sleep in the water,” said the scoutmaster. “They probably ran out of energy and died.” What seemed obvious to this man, by hindsight, had apparently stolen upon six robust campers like a Mosaic angel of death. Given the nature of hypothermia and the nature of water, it is not hard to believe.
Seventy years ago, hypothermia, like radiation sickness, was unheard of. People in those days died of consumption, yellow fever, childbirth, the flu. They also, in cases of mishap on the high seas, died of “drowning.” But drowning was merely the standard official and popular presumption, clung to for lack of a better one—live people doing their best, again, to get a grip on the lonely and personal business of death. As late as 1969, a physiologist from Oxford University, W. R. Keatinge, wrote that “until recently even experts commonly regarded drowning as the only important hazard to life in the water. Those who did look forward seldom appreciated any other hazards except thirst and attack by sharks. This belief is still common. It is almost routine for anyone who dies in the water to be said to have drowned, not only in everyday conversation and the press but often in official reports.” For example, the case of the Titanic.
It was on its maiden trip when an iceberg hit the ship. This was shortly before midnight on April 14, 1912, a chilly spring night in the North Atlantic, about 400 miles off the coast of Newfoundland, and the temperature of the water in which the Titanic sank, so quickly, was hovering around 32°F. During the early minutes of pandemonium, roughly a third of the passengers and crew managed to get safely aboard lifeboats, either dry-shod from the side of the ship itself or after a brief dunking. The other 1,489 people were left swimming, but there were far more than enough lifejackets to take care of everybody. Within just one hour and fifty minutes another ship, the Carpathia, arrived on the scene to begin scooping up survivors. Now the shocking part. The Carpathia was able to save almost all of those lucky or assertive folks who had gotten themselves places in the lifeboats; every one of the other 1,489 people, most
of them bobbing there nearby in perfectly decent lifejackets, was dead.
Afterward an official report came down from the superintendent of the Port of Southampton, under the title “Particulars Relating to the Deaths of Members of the Crew Lately on Board the S.S. Titanic.” This document included a roll of fatalities that ran nineteen pages, and after each name the cause of death was cited as drowning. In all the various investigations and reports following the Titanic disaster, according to Keatinge, there was hardly a mention of immersion hypothermia—under that phrase or any other—as a cause of or a contributing factor in death.
Nowadays scientists and maritime people know better. Perhaps no form of exposure to nature’s brutal indifference is deadlier and (aside from running afoul of a grizzly or toppling off El Capitan) swifter than hypothermia. Yet it is also insidiously subtle. About six hundred Americans die from it each year, and despite the common notion that associates hypothermia with arctic cold, most of those six hundred victims were never in any danger of frostbite. Many of them were subjected only to cool or even mild temperatures, in the forties and fifties, but for one reason or another they got caught with wet clothing in the path of brisk winds and couldn’t protect themselves until too late. Many others were simply plunked into an ocean or a stream or a lake, like the Ram Patrol, and for one reason or another couldn’t get out. They didn’t freeze to death, like that smug dude in the Jack London story “To Build a Fire,” which still represents the most widely known, and misleading, depiction of fatal hypothermia. They chilled to death. It doesn’t take long.
Most old-fashioned clothing (wool, of course, being the exception) loses up to 90 percent of its insulating value when it is wet. Put a rain-drenched mountaineer on a breeze-raked ridge and, without a windbreaker, his life will be in jeopardy within half an hour. But full immersion in water, an occupational hazard of sea travelers since the time of Noah, is deadlier still, because the thermal conductivity of water is 240 times that of air. While a man overboard sculls gently to keep his face out of the waves, rides without further effort in his lifejacket, waits hopefully for speedy rescue, the water sucks heat—and therefore life—from the core of his body at a merciless rate. Immersed in water at 32°F, like the Titanic passengers, the average human will die within an hour. Immersed at 59°F, he will die after six hours. And 59°F happens to be warmer than practically all of the coastal and inland waters of North America; in fact, it is warmer than most of the surface water on the planet ever gets (outside of the tropics) through an entire year.
No wonder shipwreck, grand and small, has killed so many good swimmers. No wonder Madame Sosostris, famous clairvoyant, wisest woman in Europe, said: “Fear death by water.”
As a body begins losing large amounts of heat to the surrounding environment, two things happen. The less serious is frostbite, in which blood circulation to the extremities is automatically reduced as a desperate measure to conserve heat; this results in a drastic differential between the temperature of the skin and the temperature of the thoracic interior, and those expendable fingers and toes are sacrificed to maintain thermal stability in the body’s vital core. The more serious phenomenon is hypothermia, occurring when no such differential, no such desperate sacrifice, can prevent the core temperature itself from plummeting. As the core temperature falls, the symptoms of hypothermic trauma develop in progressive stages. A physician and mountaineer named Ted Lathrop, in a pamphlet published by the Mazamas climbing club, has described those stages in detail.
Dropping from a normal 98.6° down to 96° at the body core, says Lathrop, the victim will show uncontrollable shivering and a distinct onset of clumsiness. From 95° down to 91° the shivering will continue, and now speech will become slurred; mental acuity will decrease; there may also be amnesia. During this stage often come those crucial mistakes in judgment that prevent a victim from taking certain obvious steps that could save him from death. Between 90° and 86° the shivering will be replaced, says Lathrop, with extreme muscular rigidity, and exposed skin will sometimes appear blue or puffy. Mental coherence may be negligible, and amnesia may be total, though the person may still be able to walk, and if he is unlucky, his companions may not yet have noticed that he is in serious trouble. Down around 81° he will slide into a stupor, with reduced rates of pulse and respiration. Two or three degrees colder than that at the body core and he goes unconscious. His heartbeat may now be erratic, yet even if it remains steady, there is a grave problem: Human blood cooled to this temperature becomes reluctant to turn loose the oxygen it’s supposed to transport, so despite continued circulation, the brain and the heart muscle may be starved of the oxygen they require. If the core temperature falls further, below 78°, those brain centers that govern heartbeat and respiration will probably give out. There will be cardiac fibrillation—that is, the heart will be gripped with disorganized spasmodic twitching. Also now, pulmonary edema and hemorrhage—the lungs suddenly filling with clear cellular liquids and blood. The person may vomit or just cough rackingly, a bit of pink foam frothing out from between his lips. And then he is dead.
The coldest spot of skin on his coldest toe may be no colder than 59°F. But his core has fallen to 75°, and all the gears have seized.
The conditions in Lake McNaughton, British Columbia, where the Ram Patrol came to their end, were more than sufficiently inhospitable to bring on this sequence of stages and to justify that surviving scoutmaster in his diagnosis. True enough, it would be hard to imagine how six healthy young men could drown under such circumstances, but not hard at all to figure how hypothermia might have killed them. The lake had gotten a bit choppy in late afternoon, and the Ram Patrol must have pulled into that cove for shelter, the scoutmaster guessed, when their canoes started taking on water. They seem to have climbed out of their boats in the shallows, he guessed, and even succeeded in dumping both canoes empty and righting them again. Or something. “Then they must have run out of energy and hypothermia set in,” said the scoutmaster to the Associated Press.
But then later that week I made a call to the coroner of Revelstoke, British Columbia, within whose jurisdiction the Lake McNaughton incident occurred. The coroner told me something different. Sometime after the first newspaper story, autopsies were performed. Hypothermia, it had been quietly concluded, was not the cause of the deaths.
The lungs of the victims were filled not with blood and clear bodily fluids but with lake water. The four boys and two men of the Ram Patrol, floating in lifejackets near their empty canoes, had all drowned.
No one knows how. No one is likely to find out. Early symptoms of hypothermia, such as lassitude or muscular rigidity, may have made some secondary contribution, said the coroner. But that, he admitted, was purely speculative. With no witnesses and no survivors, the truth could only be guessed at. Death is personal.
Is Sex Necessary?
BIRDS DO IT, BEES DO IT, or so goes the tune. But the songsters, as usual, would mislead us with drastic oversimplifications. The full biological truth happens to be more eccentrically nonlibidinous. Sometimes they don’t do it, those very creatures, and get the reproductive results anyway. Bees of all species, for instance, are notable for their ability to produce offspring while doing without. Birds mostly do mate, yes, but at least one variety—the Beltsville Small White Turkey, a domestic breed out of Beltsville, Maryland—has achieved scientific renown for a similar feat. What we’re talking about here is celibate motherhood, procreation without copulation, a phenomenon that goes by the name parthenogenesis. Translated from the Greek roots: virgin birth.
And you don’t have to be Catholic to believe in this one.
Miraculous as it may seem, parthenogenesis is actually rather common throughout nature, practiced regularly or intermittently by at least some species within almost every group of animals except (for reasons still unknown) dragonflies and mammals. Reproduction by virgin females has been discovered among fishes, amphibians, birds, reptiles,* crustaceans, mollusks, ticks, the jellyfish clan, fl
atworms, roundworms, segmented worms; and among insects (notwithstanding those unrelentingly sexy dragonflies) it is especially favored. The order Hymenoptera, including all bees and wasps, is uniformly parthenogenetic in the manner by which males are produced: Every male honeybee is born without any genetic contribution from a father. Among the beetles, there are thirty-five different forms of parthenogenetic weevil. The African weaver ant employs parthenogenesis, as do twenty-three species of fruit fly and at least one kind of roach. Gall midges of the species Miastor metraloas are notorious for the exceptionally bizarre and grisly scenario that allows their fatherless young to see daylight: M. metraloas daughters cannibalize the mother from inside, with ruthless impatience, until her hollowed skin splits open like the door of an overcrowded nursery. But the foremost practitioners of virgin birth—their elaborate and versatile proficiency unmatched in the animal kingdom—are undoubtedly the aphids.
Now no sensible reader, not even one who has chosen this book, can be expected to care much, I realize, about aphid biology qua aphid biology. But there’s a larger reason for dragging you into the subject. The life cycle of these nebbishy insects, the very same that infest rosebushes and houseplants, exemplifies not only how parthenogenesis works but also, very clearly, why evolution has devised such a reproductive shortcut.
First the basics. A typical aphid, which feeds entirely on plant juices tapped from the vascular system of young leaves, spends winter as an egg, dormant and protected. The egg is attached near a bud site on the new growth of, say, a poplar tree. In March, when the tree sap has begun to rise and the buds have begun to burgeon, the egg opens and an aphid hatchling appears, promptly plugging its sharp snout into the tree’s tender plumbing. This solitary individual aphid will be, necessarily, a wingless female. If she is lucky, she will become sole founder of a vast aphid population. Having sucked enough poplar sap to reach maturity, she produces (by live birth now, not egg-laying, and without benefit of a mate) daughters identical to herself. These wingless daughters also plug into the tree’s flow of sap, and they also produce wingless daughters—whose daughters produce more daughters, geometrically more, generation following generation until sometime in late spring, when crowding becomes an issue and that particular branch of that particular tree can support no more thirsty aphids. Suddenly there is a change: The next generation of daughters are born with wings. They fly off in search of a better situation.
Natural Acts Page 11
