title: Inclusive fitness and differential productivity across the life course determine intergenerational transfers in a small-scale human society.
abstract: Transfers of resources between generations are an essential element in current models of human life-history evolution accounting for prolonged development, extended lifespan and menopause. Integrating these models with Hamilton's theory of inclusive fitness, we predict that the interaction of biological kinship with the age-schedule of resource production should be a key driver of intergenerational transfers. In the empirical case of Tsimane' forager-horticulturalists in Bolivian Amazonia, we provide a detailed characterization of net transfers of food according to age, sex, kinship and the net need of donors and recipients. We show that parents, grandparents and siblings provide significant net downward transfers of food across generations. We demonstrate that the extent of provisioning responds facultatively to variation in the productivity and demographic composition of families, as predicted by the theory. We hypothesize that the motivation to provide these critical transfers is a fundamental force that binds together human nuclear and extended families. The ubiquity of three-generational families in human societies may thus be a direct reflection of fundamental evolutionary constraints on an organism's life-history and social organization.
authors: Department of Anthropology, Emory University, 1557 Dickey Drive, Atlanta, GA 30322, USA Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, NM 87501, USA phooper@emory.edu.
authors: Paul L
authors: PL
authors: Hooper
authors: Department of Anthropology, University of California Santa Barbara, Santa Barbara, CA 93106, USA.
authors: Michael
authors: M
authors: Gurven
authors: Department of Anthropology, Texas A&M University, Mailstop 4352, College Station, TX 77843, USA.
authors: Jeffrey
authors: J
authors: Winking
authors: Department of Anthropology, University of New Mexico, MSC01-1040, Albuquerque, NM 87131, USA.
authors: Hillard S
authors: HS
authors: Kaplan
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000383:Agriculture; D005075:Biological Evolution; D001838:Bolivia; D002648:Child; D002675:Child, Preschool; D003299:Cooperative Behavior; D004526:Efficiency; D005190:Family; D005195:Family Relations; D005247:Feeding Behavior; D005260:Female; D056084:Genetic Fitness; D006801:Humans; D007199:Indians, South American; D007223:Infant; D008297:Male; D008875:Middle Aged; D012737:Sex Factors; D012919:Social Behavior
keywords: food sharing; grandparental investment; human life history; inclusive fitness; intergenerational transfers; parental investment