1Anthropology, University of New Mexico, 2Human Evolutionary Biology, Harvard University
Friday 4:30-4:45, Galleria North
Considerable evidence suggests that the steroid hormone testosterone mediates major life-history trade-offs in primates, supporting mating effort at the expense of parenting effort and survival. Specifically, the “challenge hypothesis” posits that testosterone is elevated during life-history phases when males are competing for mating opportunities. Most wild data, however, come from short-term, cross-sectional studies that cannot track individuals across the lifespan. We used >6000 urine samples collected over 13 years from male chimpanzees living in Kibale National Park, Uganda to examine longitudinal changes in testosterone production in this species. We also employed a novel measure of urinary creatinine to track developmental changes in muscle mass. We predicted that shifts in testosterone production would correlate with male mating effort over the life course, including physiological investment in sexually dimorphic muscle, and behavioral investment in dominance striving. Our results were consistent with this prediction. Males showed steep and steady increases in testosterone from the age of 9 to 15, a period in which they began to challenge other adults for status, and rise in dominance rank. Male testosterone levels and rank peaked in the late teens/early twenties, after which both showed steady declines with age at the population level. Consistent with the challenge hypothesis, however, males who maintained high rank at older ages continued to produce high levels of testosterone. Indirect measures of muscle mass showed similar patterns.
This research was supported by the National Science Foundation Grant BCS-0849380, the Leakey Foundation, and by an American Association of Physical Anthropologists Professional Development Award.