OLDER CHIMPS BEHAVE LIKE ELDERLY HUMANS.

• Position: AGING

When humans age, they tend to favor 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 behaviors 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 work is described in the journal Science.

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

The older chimpanzees had, on average, more mutual friendships, while younger chimps had more one-sided relationships. Mutual friendships are characterized by behavior such as reciprocated grooming, whereas in lopsided friendships grooming is not always returned.

Older males also were 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. Like older humans looking for some peace and quiet, the chimpanzees showed a shift from negative to more positive interactions...