Chimpanzees can lead surprisingly long lives in the wild under the right ecological conditions, a 20-year study of a large community of our close primate relatives has found.
The study 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 on chimpanzees in Uganda's Kibale National Park are important for understanding the evolution of chimpanzee and hominin life histories, the researchers said.
"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 at Yale University in the US.
"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," said Wood.
The Ngogo chimpanzees reside in the centre of Kibale National Park, in southwestern Uganda.
The directors of the Ngogo Chimpanzee Project 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.
The study reveals that Ngogo chimpanzees have the highest life expectancy on record for any group of wild chimpanzees.
Favourable 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.
The research team argues that this rich food supply helps buffer the Ngogo chimpanzees against periods of hunger, and helps fuel their ability to stave off diseases that would otherwise lead to higher mortality.
The Ngogo chimpanzees also benefit from a low risk of predation, because leopards are not found within Kibale National Park, and from the fact that during the study, the chimpanzees did not experience major disease epidemics, either introduced by humans or due to other causes, like those that have affected wild chimpanzees at several other long-term research sites.
The Ngogo chimpanzees' higher survivorship appears to be an adaptive response to a more abundant and less varied food supply than that of Kanyawara, the researchers said.
The study was published in the Journal of Human Evolution.
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