Kanyawara chimpanzees enjoy low mortality risk

In a new study just published in the Journal of Human Evolution, KCP directors Martin Muller and Richard Wrangham examine mortality risk at Kanyawara over the past 25 years. Life history data from wild chimpanzees are important for understanding the evolution of the human life history, but previous data on chimpanzee mortality came primarily from sites that had suffered dramatic, human-induced declines, and were consequently unrepresentative of long-term patterns. The Kanyawara community, by contrast, has grown slightly over the past 25 years, avoiding both simian immunodeficiency virus and the worst impacts of human contact. Demographic data from the site are thus particularly valuable. Estimates of mortality risk in Kanyawara were substantially lower than those from other long-term sites. In the Kanyawara sample, life expectancy at birth was 19. The comparable number for a composite sample from Gombe, Tai and Mahale was 13. Kanyawara chimpanzees that lived to age 14 could expect to live for another 24 years. At other sites, they could only expect to live for another 14 years. Rates of infant mortality at Kanyawara were similar to those of the Hadza, a human foraging population. 55% of Kanyawara chimpanzees lived to age 11, compared with 59% of Hadza children in a study by Nicholas Blurton Jones. Such low mortality is good news for chimpanzee conservation, but with climate change and a growing human population in East Africa, there is no guarantee that it will continue.