The Evolution of Death: Why We Are Living Longer

Chapter 2. Charting Death’s Evolution and Life’s Extension

Chapter 2 Charting Death’s Evolution and Life’s Extension Past progress against mortality may be underestimated, and as a consequence , predictions of future progress against mortality may be too low. —J. W. Vaupel, K .G. Manton, and E. Stallard, “The Impact of Heterogeneity in Individual Frailty on the Dynamics of Mortality” Thus, we know that the upper tail of the age distribution of deaths has been moving steadily higher for more than a century. —J. R. Wilmoth and H. Lundström, “Extreme Longevity in Five Countries” He was beginning to understand that death was not simply a loss of vitality, but a profound change . . . [that] made him fear death less. You did not suffer after death. There was nothing left to suffer. —Paul McAuley, Pasquales’s Angel Death’s evolution? What irony! How could death evolve when it has no apparent benefit for the survival or reproduction of individuals? How could the manufacture of corpses, aka death, evolve? What would possibly constitute evidence for death’s evolution? Intuitively, one might suppose that the evolution of death would make life shorter and faster, for instance, via progeria disease. But if death, like everything else in life, evolves through the propagation of life, then death could 41 hardly evolve through early-onset diseases, especially where there is no offsetting balancing mechanism or even progeny to carry on the trait. And if death, like so much else in life, represents an adaptation, somehow death evolves by becoming more efficient—by allowing organisms to die only when all other alternatives have failed. Thus, counter to intuition, death would have to evolve by forestalling the metamorphosis of organisms into corpses! A physical metaphor might help clarify the idea of death evolving by prolonging life. Remember (or don’t remember if it’s too painful) your introductory physics lab (or imagine one if you never took physics with lab): You rolled a marble down an inclined plane (actually a grooved track) and measured how far the marble rolled after reaching a level plane (actually a table top). Had the instructor permitted, you might then have rolled two identical marbles down two identical tracks, except marble #1 rolled on a smooth track and marble #2 on a rough track. The force of gravity accelerating the two marbles would be the same, but marble #1 would encounter less friction (resistance ) and travel farther than marble #2 on the level plane. Now imagine two lives rolling down two lifecycles, life #1 rolling on a well-lubricated lifecycle, and life #2 rolling on a poorly lubricated lifecycle. Just as marble #1 rolled for a greater distance than marble #2, life #1 lasts longer than life #2, that is, the organism on the well-lubricated lifecycle lives longer than the organism on the poorly lubricated lifecycle. Let us say, by way of illustration, that the lifetime on the well-lubricated track turns out to be twice as long as the lifetime on the poorly lubricated track. For example, if life #1 travels two units of life while life #2 travels only one unit, life #1 will be twice as long as life #2. Moreover, the corollary is also true: life on the poorly lubricated lifecycle (traveling one lifetime per unit of life) proceeds at twice the rate as life on the well-lubricated lifecycle (one lifetime per two units of life). This is only to say that longer life proceeds more slowly! What it boils down to in terms of Darwinian fitness is quite straightforward if counterintuitive: all else being equal, where death is evolving, the duration of lifetimes is increasing and the rate of living is decreasing. Thus, longer life and slower living are the qualities that one would look for were death evolving. MEASURING DEATH’S EVOLUTION: EMPIRICAL EVIDENCE Death’s competitive advantage is readily traced in Homo sapiens, since a great deal is known about human longevity. The fact is, we are big winners in the race toward longer and slower lifetimes! Contemporary human beings have a remarkably long lifetime—with a median of nearly eighty years or thereabouts in developed countries. Indeed, with the possible exception of the bowhead whale, human beings are the longest living mammals on Earth. In contrast, our 42 HOW BIOLOGY MAKES SENSE OF DEATH ancient reptilian cousins, the dinosaurs, seem to have died young: bones from the oldest-known Tyrannosaurus rex (Field Museum, FMNH PR2081) indicate that it died...