Grandparenting and the evolution of post-menopausal lifespan

Hillard S. Kaplan, University of New Mexico
Michael D. Gurven, University of California, Santa Barbara
Jeff Winking, University of New Mexico

This paper presents some initial tests of alternative explanations for the extension of the human lifespan, using data collected among Tsimane horticulturalists in lowland Bolivia. The “grandmother hypothesis” proposes that older women increase offspring fertility and grandoffspring survivorship through provisioning. The “embodied capital” theory proposes that a shift in productivity from younger to older ages selects for increased investments in survival and longevity. The patriarch hypothesis proposes that an extended lifespan provides direct reproductive benefits to men, who do not experience reproductive cessation. Finally, the mother hypothesis argues that most direct care of offspring will come from mothers, and extended lifespan is due to long term child dependence. First, we test predictions regarding the behaviour of older people with respect to descendent kin. Second, we measure the effects of older individuals’ survival and co-residence, as they vary by sex, on children’s survival, morbidity and growth rates.