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EVOLUTION OF HUMAN HEALTH

How natural selection shapes our later years

Nature Ecology & Evolution volume 5, pages 271–272 (2021)Cite this article

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Natural selection does not disappear with age, according to a new evolutionary demographic model. This conclusion is at odds with the widespread belief that ending reproduction relaxes purifying selection on alleles that increase our ageing body’s vulnerability to diseases such as cancer, Alzheimer’s or diabetes.

The prediction of the inevitable decline of selection with age made by classical theories of senescence1,2,3,4 has been shaken recently. Senescence is not detected at all in many plants and animals5. Although humans are not among these, there are two socio-demographic factors that can, in principle, increase the fitness of those who live long and in good enough health to give a late impetus to their descent. First, men’s fecundity does not halt abruptly at around age 45 as it does in postmenopausal women. This can result in male-driven selection for alleles extending lifespan beyond this age in both sexes6. Second, by providing care to younger parents, a person may increase her own inclusive fitness. Coined the ‘grandmother hypothesis’7 in reference to older women helping to raise their grandchildren, this phenomenon falls into the category of indirect genetic effects (IGE). That is, when there is a positive genetic correlation between the lifespan of caregivers and the fitness of kin receiving care, selection for longer lifespan is possible8. Logically, these two factors could trigger purifying selection against alleles that increase susceptibility to late-onset diseases that reduce survival or the ability to provide care. A third factor also plausibly generates covariance between disease expression and fitness: the larger the variance in the age at disease onset, the greater the chance that some individuals become ill before ceasing reproduction. For example, breast and ovarian cancers strike some women in their twenties, even though the mean age at onset is generally over 50 for these diseases.

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Fig. 1: How purifying selection at older ages could shape the genetic architecture of late-onset diseases.

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  1. Department of Chemistry, Biochemistry, and Physics, Université du Québec à Trois-Rivières, Trois-Rivières, Québec, Canada

    Emmanuel Milot

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  1. Emmanuel Milot
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Correspondence to Emmanuel Milot.

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Milot, E. How natural selection shapes our later years. Nat Ecol Evol 5, 271–272 (2021). https://doi.org/10.1038/s41559-020-01374-z

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