Journal of Hum

ia ria based on the principle that these anatomical features play a role in sex-specific reproductive effort (Plavcan, 2000). Evidence about the developmental processes yielding sex and species differences further contributes to interpreting their behavioral or functional implications. In the case of differences between chimpanzees Leigh, 1998), canine dimorphism arises mostly prior to puberty as a result of bimaturism (Schwartz et al., 2001). The timing and ontogenetic processes resulting in body size and canine sex dimor-phism appear to vary across primates, and even within the homi-noids (Leigh andShea,1996; Schwartz et al., 2001; Leigh et al., 2005). Wehypothesized that the differences in both social behavior and sex dimorphism that distinguish chimpanzees and bonobos also arise in part due to prenatal androgens, implying a potential role for endo-crine system changes in the evolution of chimpanzees and humans. * Corresponding author. Contents lists availa