More Modeling of the Grandmother Hypothesis

We humans live for much longer than the other large primates, and the grandmother hypothesis suggests that this longevity evolved because of our greater capacity for culture, cooperation, and communication. Once we became intelligent enough for older and less physically capable individuals to nonetheless materially assist in the survival of their descendants, longer lives were selected for.

As is the case for other theories in the evolution of aging, simulation is used to investigate the grandmother hypothesis and bolster arguments on interpretation and plausibility. Here, the researchers suggest that enhanced longevity in our ancestors in comparison to their primate peers may have predated our species:

We present a mathematical model based on the Grandmother Hypothesis to simulate how human post-menopausal longevity could have evolved as ancestral grandmothers began to assist the reproductive success of younger females by provisioning grandchildren. Grandmothers' help would allow mothers to give birth to subsequent offspring sooner without risking the survival of existing offspring. Our model is an agent-based model (ABM), in which the population evolves according to probabilistic rules governing interactions among individuals. The model is formulated according to the Gillespie algorithm of determining the times to next events. Grandmother effects drive the population from an equilibrium representing a great-ape-like average adult lifespan in the lower twenties to a new equilibrium with a human-like average adult lifespan in the lower forties.

The stochasticity of the ABM allows the possible coexistence of two locally-stable equilibria, corresponding to great-ape-like and human-like lifespans. Populations with grandmothering that escape the ancestral condition then shift to human-like lifespan, but the transition takes longer than previous models. Our simulations are consistent with the possibility that distinctive longevity is a feature of genus Homo that long antedated the appearance of our species.


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