Male mating choices: The drive behind menopause?

When we examine the life history of humans against our closest primate relatives, the other great apes, there is notably a greater longevity in humans which includes a distinctive postmenopausal life stage, leading to the question, "How did human females evolve to have old-age infertility?" In their paper "Mate choice and the origin of menopause" (Morton et al., 2013), Morton et al. developed an agent-based model (ABM) to investigate the novel hypothesis that ancestral male mating choices, particularly forgoing mating with older females, were the driving force behind the evolution of menopause. From their model, they concluded that indeed male preference for young female mates could have driven females to lose fertility at older ages through deleterious mutations, leading to menopause. In this work, we revisit their male-mate-choice hypothesis by formulating an analogous mathematical model using a system of ordinary differential equations (ODEs). We first show that our ODE model recreates the qualitative behaviour and hence conclusions of key scenarios in Morton et al. (2013). However, since our ODE system is less computationally demanding than their ABM, we also conduct a broader sensitivity analysis over a range of parameters and differing initial conditions to analyse the dependence on their conclusions to underlying assumptions. Our results challenge those of Morton et al. as we find that even the slightest deviation from an exclusive mating preference for younger females would counteract the evolution of menopause. Consequently, we propose that their male-mate-choice hypothesis is incomplete and needs further explanation of how a male strategy to exclusively mate with young females could have arisen in our common ancestors and remained evolutionarily stable for long enough to drive the evolution of old-age female infertility.

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