Aging and friendship? Ask the chimp

    Images of three male Aging Chimps
    Three males groom together in a chain — Likizo (a younger male) grooms Big Brown (an older male), who grooms Lanjo (another younger male). Photo by John Lower

    When humans age, they tend to favour small circles of meaningful, established friendships rather than seek new ones, and to lean toward positive relationships rather than ones that bring tension or conflict. These behaviours were thought to be unique to humans but it turns out chimpanzees, one of our closest living relatives, have these traits, too.

    Understanding why can help scientists gain a better picture of what healthy aging should look like and what triggers this social change.

    The study draws on 78,000 hours of observations, made between 1995 and 2016. It looked at the social interactions of 21 male chimpanzees between 15 and 58 years old in the Kibale National Park in Uganda. It shows what’s believed to be the first evidence of nonhuman animals deliberately selecting who they socialize with during aging.

    The researchers looked only at male chimpanzees because they show stronger social bonds and have more frequent social interactions than female chimps. Analysing a trove of data, the researchers saw that the chimpanzees displayed much of the same behaviour aging humans exhibit.

    The older chimpanzees they studied, for instance, had on average more mutual friendships while younger chimps had more one-sided relationships. Mutual friendships are characterized by behaviour such as reciprocated grooming whereas in lopsided friendships grooming isn’t always returned.

    Older males were also more likely to spend more time alone and showed a preference for interacting with — and grooming — chimps they deemed to be more important social partners, like other aging chimps or their mutual friends. And like older humans looking for some peace and quiet, the chimpanzees showed a shift from negative to more positive interactions as they reached their twilight years. The preference is known as a positivity bias.

    “The really cool thing is that we found that chimpanzees are showing these patterns that mirror those of humans,” said Alexandra Rosati ’05, an assistant professor of psychology and anthropology at the University of Michigan and one of the paper’s lead authors.

    Future research can help determine if these behaviors constitute the normal or successful course that aging should take, she added. It can serve as a model or baseline.

    “There’s really a pressing need to understand the biology of aging,” Rosati said. “More humans are living longer than in the past, which can change the dynamics of aging.”

    This Research was carried out by a team of psychologists and primatologists, including current and former researchers from the Harvard Department of Human Evolutionary Biology. This article was originally posted on 

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