In this talk, Chris Kuzawa (Northwestern Uni) argues that human body fat co-evolved not just with the energetically-demanding and vulnerable brain, but also with the cultural strategies that humans use to buffer offspring intake. The human infant's need for ample baby fat traces to the fact that the main causes of nutritional stress at this age are infections, which force a reliance on onboard energy by reducing appetite and impairing digestion. However, by early childhood, we are less reliant upon this resource as a result of another uniquely human buffering system: food sharing and our cooperative strategy of caring for and feeding our young. (#30218)