A 20-year demographic study of a large chimpanzee community in Uganda's Kibale National Park has revealed that, under the right ecological conditions, our close primate relatives can lead surprisingly long lives in the wild. The study, published March 19 in the Journal of Human Evolution, establishes an average life expectancy of about 33 years in its sample of 306 chimpanzees, nearly twice as high as that of other chimpanzee communities and within the 27- to 37-year range of life expectancy at birth of human hunter-gatherers. These findings are important for understanding the evolution of chimpanzee and hominin life histories, the researchers argue.
"Our findings show how ecological factors, including variation in food supplies and predation levels, drive variation in life expectancy among wild chimpanzee populations," said Brian Wood, assistant professor of anthropology at Yale University, the study's lead author. "They also inform the study of the evolution of human life history, helping us to imagine the conditions that could have changed mortality rates among our early hominin populations." The Ngogo chimpanzees reside in the center of Kibale National Park, in southwestern Uganda. The directors of the Ngogo Chimpanzee Project—David Watts (Yale), John Mitani (University of Michigan), and Kevin Langergraber (Arizona State University)—have monitored births, deaths, immigrations, and emigrations in the unusually large Ngogo chimpanzee community since 1995, producing the largest demographic dataset available for any community of wild chimpanzees. This study reveals that Ngogo chimpanzees have the highest life expectancy on record for any group of wild chimpanzees. Favorable ecological conditions largely account for the Ngogo community's high life expectancy, according to the study. The forest in Ngogo provides a relatively consistent and abundant supply of high-energy and nutritious foods, including easily digestible figs.