The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Do Kenyan grandparents invest in their grandchildren according to evolutionary predictions?


Department of Social Medicine, Ohio University

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There are various debates on grandparent investment in relationship to increased longevity and menopause. While the grandparent investment may not been the ultimate cause of such characteristics, grandparents do assist with the care of young children; this is particularly true within the context of HIV/AIDS caregiving. With the death of adult children, grandparents have a limited ability to increase their inclusive fitness other than to ensure that orphans survive and reproduce. Thus you would expect that the level of investment will be greater in orphans than non-orphans. At the same time, level of genetic relatedness, paternity certainty and sex-specific reproductive strategies will lead differential investment based on the specific relationship of the grandparents to the grandchild. To examine these predictions, the caregiving investment of 387 Kenyan grandparents was explored using energy expenditure and caregiving intensity. Results indicate that energy expenditure was higher among caregiving women. Among grandmothers, energy expenditure increased with the number of paternal orphans in the homestead. The number of pre-teens was associated with an increase in energy expenditure, while there was no impact of teenagers or children under 5 years. In support of the Trivers-Willard effect, the number of girls in the homestead predicted energy expenditure, while there was no impact of the number of boys. This association was only present among caregivers. Results from caregiving investment were overall similar. These data suggest that grandparents invest in their grandchildren in patterns partially supportive of evolutionary predictions.

This research was supported by NSF grant # 0515890.

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