1Dept of Biological Sciences, University of Southern California, 2Davis School of Gerontology, University of Southern California
Friday 10:00-10:15, Ballroom A
The benefits accruing to alpha males in primate social groups have been debated for many years. In wild chimpanzees, alphas may reap enhanced reproductive success and resource access, but also incur increased cortisol levels and a higher parasite load, in addition to a greater risk of injury. We surveyed published data from five long-term chimpanzee study sites on 17 alpha male tenures and longevity compared to the longevity of 14 males who never reached alpha rank. We excluded males with unknown life histories and those that did not reach adulthood. The life expectancy for males that reached age 15 was 14.3 years (equals an overall lifespan of 29.3 years), similar to the result reported by Hill et al. (2001). Adult life expectancy was 33.4 years for alpha males (n = 17), versus 24.4 years for never-alphas (n = 14; ty = 3.17, p = .005). Alpha males were deposed at a mean age of 29.3 years, on average 6 years after achieving alpha status. Alpha males live on average an additional 4 years after being deposed compared with their never-alpha counterparts. Fifty-nine per cent of alphas outlived the oldest never-alpha male in the dataset.
We discuss possible explanations for the correlation between alpha status and extended life expectancy, including the parallel with humans. Alpha male chimpanzee status is more fluid and less stable than is reported in human demographic studies. We consider the evolutionary similarities and contrasts between nonhuman primate and human cases.