New research has revealed that like humans, chimps concentrate on fewer friends and behave less aggressively as they age. When humans age, they tend to favor small circles of meaningful, already established friendships rather than seek new ones. People are also more likely 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. The study shows what’s believed to be the first evidence of nonhuman animals actively selecting who they socialize with during aging.
The study draws on 78,000 hours of observations, made between 1995 and 2016, which looked at the social interactions of 21 male chimpanzees between the ages of 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 actively 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.
Analyzing a trove of data, the researchers saw that the chimpanzees displayed much of the same behavior aging humans exhibit. The older chimpanzees they studied, for instance, preferred spending more time with — and grooming — chimps they’d developed mutual friendships with over the years while younger chimps had more one-sided relationships where grooming wasn’t always returned. Older males were also more likely to spend more time alone but interacted with more important social partners, like their aging mutual friends. And like older humans looking for some peace and quiet, the chimpanzees also showed a shift from negative interactions to more positive ones as they reached their twilight years. The preference is known as a positivity bias.
Journal Reference: Alexandra G. Rosati, Lindsey Hagberg, Drew K. Enigk, Emily Otali, Melissa Emery Thompson, Martin N. Muller, Richard W. Wrangham, Zarin P. Machanda. Social selectivity in aging wild chimpanzees. Science, 2020; 370 (6515): 473. Summary.
Also: NYT piece