1Human Evolutionary Biology, Harvard University, 2Evolutionary Anthropology, Duke University
Friday 2:30-2:45, Galleria North
Patterns of skeletal, behavioral, and cognitive development have been found to differ between humans’ two closest living relatives, chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). In particular, aspects of mating behavior and male aggression have changed significantly between the two species, suggesting a potential link between the production of testosterone and these shifts in developmental trajectories. Here we tested this hypothesis by measuring the ontogeny of testosterone production in chimpanzees and bonobos ranging from infancy to adulthood, utilizing a method of salivary steroid analysis validated by previous work. We also collected data on body weight in the two species across the same age range to provide a general growth index. We found that among chimpanzees, juvenile testosterone levels were low and both sexes showed markedly increased testosterone production during adolescence (males more so than females). In contrast, among bonobos, testosterone levels remained consistent throughout infancy, juvenility, and the transition to adulthood. The stability of testosterone production during bonobo development was not associated with stunted growth in our study population; data on body weight revealed that chimpanzees and bonobos showed broadly similar patterns of growth, with chimpanzees larger at every age. These results suggest that if elevations in testosterone occur during puberty in bonobos, they are short-lived. They also indicate that the ontogenetic pattern of testosterone production can be subject to rapid evolutionary change. In the case of bonobos and chimpanzees, changes in the developmental trajectories of testosterone production may provide one mechanism underlying broader developmental differences between the two species.
This work was supported in part by a European Research Commission Advanced Grant Agreement 233297 and National Science Foundation grant NSF-BCS-08-27552-02 to B.H, and an L.S.B. Leakey Foundation Grant, NSF DDIG 0851291, and Wenner-Gren Foundation Grant to V.W.