Grandmothering

Introducing grandmothering allowed the population to move from great-ape-like to hunter-gatherer-like longevity while keeping age at last birth similar. The study argues that grandmothering can drive longer human-like adult survival without requiring later female fertility cessation. Repeated increases in female-to-female interaction in older ages were linked to the grandmothering effect. Grandmother-care alone had only a small effect on infant survivorship because infants are less likely to have a living grandmother than a living mother. Grandmother-care combined with long-term care of adult offspring produced extensive PRLS. In the model, grandmothering is limited to post-fertile females who support only their daughters. Grandmothering is proposed to increase older women's inclusive fitness by helping daughters reproduce sooner while dependent juveniles still need support. The increase in long female-to-female calls was interpreted as daughter-mother interaction and evidence that grandmothering-related communication had begun. Grandmother-care can become more efficacious at later ages because its benefits accumulate across descendants through daughters. Grandmother-care proposes…