Chimps, Like People, Get Picky About Friends as They Age

They prefer to spend time with just a few positive pals.

Common chimpanzees grooming each other
Older chimps typically have reciprocal relationships where they groom each other. Anup Shah / Getty Images

As people get older, the types and numbers of friends they have tend to change. As young adults, humans have large groups of friends. With age, they often prefer to spend their time with just a few close, positive individuals.

Researchers long believed that this aging attraction toward meaningful relationships was unique to humans, but a new study finds that chimps also have similar tendencies.

One explanation for the human inclination to get pickier about social connections has to do with awareness of mortality. As people age, they don’t necessarily want to be surrounded by a large group of negative friends, but would prefer just to be near a handful of close, upbeat individuals.

“Socioemotional selectivity theory proposes that people monitor how much time we have left in our life and prioritize emotionally-fulfilling relationships in old age when time is perceived to be running out,” one of the study’s lead authors Alexandra G. Rosati, a psychologist and anthropologist at the University of Michigan, tells Treehugger.

“The claim is that these changes in friendships depend on a sense of future personal time and awareness of one's mortality.”

Rosati and her colleagues were curious whether chimps would show similar traits even though they don’t seem to have the same impending sense of mortality.

They used 78,000 hours of observations made over 20 years from the Kibale Chimpanzee Project in Uganda. The data looked at the social interactions of 21 male chimps between 15 and 58 years old. The researchers only studied male chimps because they demonstrate stronger social bonds and have more social interactions than female chimps.

Researchers found that wild chimpanzees share a similar pattern of social aging with humans, Rosati says.

“They prioritize strong, mutual social bonds and interact with others in more positive ways as they get older. Younger adults, in contrast, were more likely to form lopsided relationships where their partner did not reciprocate and show more aggression.”

The older chimpanzees preferred spending more time with chimps that they had become friends with over the years. They would sit close to these long-time companions and groom each other. By contrast, younger chimps had more one-sided relationships where they would groom a friend, but the action wasn’t returned.

Older male chimps were also more likely to spend more time alone. The researchers said that they showed a shift from negative interactions to more positive ones, preferring to spend their later years in nonconfrontational, upbeat relationships. Researchers call the preference a “positivity bias.”

The study was published in the journal Science.

Understanding Healthy Aging

Researchers theorize that chimps, like humans, are able to change their social focus as they age.

“We propose that this aging pattern may be the result of shared changes in our abilities to regulate our emotions with age,” Rosati says. “This shared pattern between chimpanzees and humans could represent an adaptive response where older adults focus on important social relationships that provide benefits and avoid interactions that have negative consequences as they lose competitive fighting ability.”

Understanding why these behaviors occur can help scientists understand healthy aging and what triggers this change in social interaction.

“This study shows how long-term behavioral datasets from wild animals like chimpanzees can help us understand and promote healthy aging in humans,” Rosati says. “In addition, it highlights that our changes in behavior in old age, such as our shrinking social networks and prioritization of strong existing social bonds, represent changes in healthy aging that are shared in other species as well.”