Figure 1.

Antagonistic pleiotropy theory of ageing (AP) is a population genetic theory, which maintains that selection favors alleles that increase fitness in early life at the expense of fitness in late life because the force of selection on traits declines with age (Williams 1957). There are two main routes in which AP alleles can operate. First, AP alleles can control allocation of limited resources between life‐history traits. For example, the “disposable soma” theory (DST) (Kirkwood 1977), a physiological theory of ageing, is based on the putative trade‐off between resource allocation to growth, reproduction, and somatic maintenance. Under the DST, alleles that increase allocation to rapid growth and early‐life reproduction at the cost of late‐life survival and reproduction can be favored by selection. The recently proposed hypothesis that selection can favor increased early‐life survival at the cost of reduced late‐life survival is another special case of how AP can work via resource allocation (Omholt and Kirkwood 2021). All resource allocation versions of AP share the same underlying mechanism—insufficient resources that are optimally allocated across life‐history traits to maximize fitness, resulting in insufficient resources for somatic maintenance and repair. Second, AP alleles can cause late‐life damage by continuing to function in a way that was beneficial in early life but detrimental in an adult organism (“early‐life inertia” theories of ageing). For example, natural selection on gene expression is maximal in early life, from development until the age of first of reproduction, and is expected to decline after the onset of reproduction (Hamilton 1966). Insufficient selection on gene expression can result in suboptimal levels of gene expression in late life leading to senescence. There are several different hypotheses that have been proposed, for example, the developmental/programmatic theories of ageing (de Magalhaes and Church 2005; de Magalhaes 2012; Gems and de Magalhães 2021) and hyperfunction (Blagosklonny 2006, 2010). All these theories share the same underlying principle that natural selection optimizes organismal physiology for development and early‐life reproduction and fails to regulate late‐life performance (Maklakov and Chapman 2019).