Why Aging?

Why do organisms age? At the cellular and bacterial level, one can argue that aging is an inevitable evolved optimization that aims to carefully distribute biochemical damage to best ensure the continuing survival of a line of descent. But how and why did evolution favor aging in higher animals? Here's one line of thought: researchers "postulate that senescence could have evolved in order to prevent the spread of disease epidemics in populations ... Population density is a robust measure of fitness. But, paradoxically, the risk of lethal epidemics which can wipe out an entire population rises steeply with population density. We explore an evolutionary dynamic that pins population density at a threshold level, above which the transmissibility of disease rises to unacceptable levels. Population density can be held in check by general increases in mortality, by decreased fertility, or by senescence. We model each of these, and simulate selection among them. In our results, senescence is robustly selected over the other two mechanisms, and we argue that this faithfully mirrors the action of natural selection. This picture constitutes a mechanism by which senescence may be selected as a population-level adaptation in its own right."

Link: http://ouroboros.wordpress.com/2009/06/04/did-aging-evolve-to-prevent-epidemics/

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