Mathematical modelling of human life history evolution

When we examine the life history of humans against our close primate relatives, the great apes, we see that human adult lifespans include a post-menopausal life stage.

Morton et al., using an agent-based model, proposed that a higher preference of males to mate with younger females led to the evolution of old-age infertility in the human population. However, as it is difficult to analyse an agent-based model, we propose an analogous system of ordinary differential equations (ODE) to examine their conclusions.

We present four ODE models that aim to investigate the proposition of Morton et al. of whether it is plausible that ancestral male mating choices, particularly forgoing mating with older females, was the driving force behind the evolution of menopause. The four models, which increase in complexity, suggest that the evolution of menopause is unlikely to be due to male mate choice. For old-age infertility to become dominant in the population, all males must pursue an evolutionarily inferior and unrealistic decision to restrict their mating preferences to only young females. In our models, even the slightest deviation from an exclusive mating preference for younger females would counteract the evolution of menopause. Our conclusion contradicts that of Morton et al., therefore further investigation is needed.

Instead, we believe that the grandmother hypothesis, which proposes that post-fertile females’ provisioning of juveniles to ensure their survival could provide a more plausible explanation of the evolution of human post-menopausal lifespans. As a next step, we will develop mathematical models to quantitatively investigate this theory.