A Means to an End: The Biological Basis of Aging and Death

A major question that troubles those who think deeply about the evolutionary origins of senescence and death is the biological basis for the tremendous variability in maximum lifespan seen between species living in the same environmental niche. Why do some species live so much longer than others? How could such differences have arisen in the first place? Maximum lifespan will certainly be affected to some extent by variability in the rate at which senescence results in death, either through accident or collapse of internal systems, once it sets in. But perhaps more important, variability in maximum lifespan seems to reflect the variability in the time after birth before individual members of a given species reach reproductive maturity. Evidence gathered across a wide range of species suggests that truly “serious” senescence is delayed until at least the beginning of the reproductive period. To understand this latter point fully, let us explore for a moment not the development of senescence in different species through the course of evolutionary time (the phylogeny of senescence)

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