The Evolution of Post-Reproductive Lifespan

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

We present initial tests of alternative explanations for the extension of the human lifespan, using data collected among Tsimane. 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. The “mother hypothesis” argues that direct care of offspring will come from mothers, and extended lifespan is due to long-term child dependence. First, we test predictions regarding the behavior of older people with respect to descendent kin. Second, we measure the effects of older individuals’ survival on children’s survival and morbidity. Third, we examine how absolute levels of resource production and investment in descendants change with the increasing age, and dependency, of grandparents.

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Presented in Session 91: On the Nature of Intergenerational Transfers