Abstract # 220:

Scheduled for Monday, September 21, 2009 01:30 PM-01:40 PM: Session 24 (Shell Room) Oral Presentation


B. House and J. Silk
Department of Anthropology, University of California, Los Angeles, Los Angeles, CA, USA

Humans (Homo sapiens sapiens) often engage in prosocial behaviors that benefit others. These behaviors are difficult to explain, however, because often the beneficiaries are unknown to the actors and don’t directly reciprocate. Among non-human primates, prosocial behaviors are typically limited to familiar group members: close kin, mates, or reciprocating partners. Recent experiments have explored how we came to be such an unusual species by examining the prosocial preferences of human children and non-human primates in laboratory settings. If our prosocial preferences were inherited from an ancestral primate, then we might expect to also observe them in chimpanzees (Pan troglodytes). Surprisingly, we found that chimpanzees showed no preference for prosocial outcomes when given the opportunity to provide rewards to familiar individuals at virtually no cost to themselves (Silk et al., 2005; Vonk et al., 2007; Brosnan et al., in press). However, we found that in a comparable experimental context 4-8 year-old children strongly prefer prosocial outcomes, delivering benefits to age-matched peers more often when the peer will receive the benefit than when the peer will not receive the benefit [β=0.48; p=0.025]. This demonstrates that even young human children have stronger prosocial preferences than do chimpanzees. Since human prosocial preferences emerge very early in development and aren’t shared with chimpanzees, these results suggest that these preferences may be unique to our evolutionary lineage.