MPIDR Working Paper

Human longevity and post-fertile survival are not predicted by primate allometric patterns

Abstract

The tendency of women to outlive their own fertility has been explained allometrically, with age at reproductive cessation attributed to ovarian follicle depletion in allometrically appropriate ovaries, and longevity related to brain and body scaling. However, because women's age at reproductive cessation is extraordinarily early compared to their longevity, we question whether both of these aspects of our demography can be predicted from primate allometric patterns. We employ a measure of longevity more useful for interspecies comparisons than the traditionally used maximum longevity to examine these allometric patterns. Using information-criterion based model selection, we find that brain size alone, rather than body size or their combined effects, produces preferred predictive models of longevity and of age at reproductive cessation. These models predict human longevity of 54-60 years, well below observed values, but accurately predict women's age at reproductive cessation. Rejecting previous conclusions, we find that human longevity, and; therefore, human post-fertile survival, are not predicted by primate patterns. We suggest that women's allometrically inappropriate longevity, and post-fertile survival, cannot be sufficiently explained in terms of proximate and phylogenetic constraints, and must be explained in terms of the unusual selective costs and benefits experienced by older women.