Does grandparental care select for a longer lifespan in non-human mammals?

Abstract

Abstract Several non-human mammalian species provide grandparental care but remain fertile until death, unlike our species. This might call into question the ‘grandmother hypothesis’ that the ability to provide grandparental care, associated with an increase in the cost of breeding with age, promote the early cessation of reproduction. Here, we analyse individual longevity records from non-human mammals to determine whether the few species with grandparental care also stand out among mammals in terms of age-specific survival patterns. Indeed, females of species with grandparental care lived on average 43% longer than males (range: 24–61%), compared with 12% in other polygynous species (95% quantile: −8 to 30%), because of low baseline mortality rates and delayed onset of actuarial senescence. We discuss this finding with respect to the ‘stopping early’ vs. ‘living longer’ debate. We review the role of the environmental context and of the decrease in offspring performance with maternal age (Lansing effect). We formalize the idea of a continuum of parental–grandparental allocation instead of a discrete switch to grandparental care only. Lastly, we suggest that the evolution of menopause has been driven by different forces in different species.