The 84th Annual Meeting of the American Association of Physical Anthropologists (2015)


How evolutionary changes in human life histories affect juvenile energetics

KAREN L. KRAMER.

Department of Anthropology, University of Utah

March 26, 2015 9:30, Grand Ballroom D Add to calendar

Human life histories have evolved in ways that significantly affect the energy and time parents allocate to rearing offspring. The energetic lives of juveniles also have changed substantially during hominin evolution. Juveniles in the past were likely self-sufficient at a young age and the direction of selection has been toward a longer period of dependence. Because modern juveniles are subsidized, it is often assumed that they increase the energetic burden on mothers, which in the past either limited surviving fertility or selected for adult cooperation. These assumptions in part stem from the analytic approaches used to quantify the cost of children. Most analyses have focused on food returns, measures of parental net investment, and analogies from ethnographic populations. From this perspective, juveniles appear expensive and a constraint on maternal investment budgets. In this paper, I reevaluate assumptions about juvenile dependence by constructing a model that: 1) uses energy-adjusted time budgets as a more sensitive measure of costs and investments; 2) accounts for the effects of overlapping offspring; 3) varies juvenile dependence to simulate the evolutionary transition from a juvenile who is self-provisioning at a fairly young age to one who is dependent until older ages. When the cost of children is simulated through evolutionary changes in birth intervals, dispersal ages and juvenile dependence, model results show that under a range of early life history changes, juveniles pay for themselves. Only under more derived life history conditions do overlapping offspring present a constraint for mothers and pressure to recruit adult cooperation.

Funding Sources: National Science Foundation, National Institutes of Health, Harvard University