Evolution And Evolution

Senescence, usually defined as progressive loss of fertility and increasing probability of death with increasing age (Kirkwood and Austad 233), is clearly a process detrimental to an individual – and, at first glance, hard to reconcile with the process of natural selection ,which would work towards ensuring optimal survival and increasing fitness (reproductive success). It seems, at a cursory glance, that it would also work towards preventing the aging process because aging leads to increased mortality rates and decreased reproductive capability.

Historically, the first attempt to explain aging from an evolutionary perspective was proposed as the “mutation accumulation” theory, which posits that the force of natural election decreases with age, allowing the accumulation of deleterious genes with age-specific effects on mortality rate. In other words, natural selection is quite effective at eliminating alleles that have deleterious effects early in life, but late in life its force diminishes; evolution allows the accumulation of deleterious alleles by a combination of mutation pressure and genetic drift, unopposed by natural selection (Rose 363-371). This idea, as sketchy as is was unsubstantiated, was further developed into “antagonistic pleiotropy” hypothesis, which basically argues that natural selection favors alleles that have aging as a side-effect, provided they had beneficial effect during youth - they exhibit pleiotropic, or opposite effects at different calendar ages, and senescence is basically a “maladaptive byproduct of selection for survival and reproduction during youth” (Fabian and Flatt).

These theoretical insights form a basis for the evolutionary theory of senescence that explains why aging is occurring. To fur...

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...xclusive and they both can account for the occurrence of senescence. They are also not the only ones that contribute to explaining why we age – “the disposable soma theory of aging” is yet another of the concepts that can contribute to the understanding of senescence, but it is a concept based on ecological factors, and the first two theories provide groundwork for the evolutionary theory of aging.

Works Cited:

Fabian, Daniel and Flatt, Thomas. ‘The Evolution of Aging’. Nature Education Knowledge 3.10 (2011)

Kirkwood, Thomas B.L., and Steven N. Austad. 'Why Do We Age?'. Nature 408.6809 (2000): 233--238. Print.

Masoro, Edward J. Challenges of Biological Aging. New York: Springer Pub. Co., 1999. Print.

Rose, Michael R., Molly K. Burke, Parvin Shahrestani, and Laurence D. Mueller. "Evolution of ageing since Darwin." Journal of Genetics 87.4 (2008): 363-371. Print.