Department of Anthropology

Cooperative breeding and adolescent siblings: Evidence for the ecological constraints model?

Hagen EH and Barret HC 2009. Cooperative breeding and adolescent siblings: Evidence for the ecological constraints model? Current Anthropology, 50, 727-737.

In humans, alloparents are usually thought to be grandmothers and adolescent girls. Although many studies have examined the impact of grandmothers on child outcomes, fewer have explored the impact of adolescents on such outcomes. We tested the hypothesis that, in a community of Ecuadorian Shuar hunter-horticulturalists, adolescent girls would have a positive impact on the growth and development of younger siblings. We measured height, weight, and skinfold thicknesses of 72 children and young adults, and computed body mass indices (BMI). Contrary to predictions, adolescent girls had a strong, significant negative impact, and boys a positive impact, on child growth and nutrition: the age-standardized BMI of children with all adolescent sisters was 1.7 standard deviations below the the age-standardized BMI of children with all adolescent brothers. In this population, adolescent girls have many mating opportunities, whereas adolescent boys do not. It is therefore possible that instead of pursuing marriage opportunities adolescent boys might have invested in younger siblings.

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Associated research project: Child nutrition and growth: Parental investment and life history theory approaches