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Chimps focus on positive relationships in old age

Kanyawara chimpanzee triad grooming: Three males groom together in a chain—Likizo (a younger male) grooms Big Brown (an older male), who grooms Lanjo (another younger male). (Credit: John Lower)

As they get older, wild chimpanzees seek interactions with other group members in increasingly positive ways, a new study shows.

Humans prioritize close, positive relationships during aging, which can support physical and mental health. The researchers have now found these social aging behaviors in wild chimpanzees.

The study, published in Science, uses data from the Kanyawara chimpanzee community living in Kibale National Park in Uganda. Scientists with the Kibale Chimpanzee Project have studied the animals for decades, and researchers of the current study used this long-term dataset to test socio-emotional selectivity theory.

An older chimpanzee lays on the ground
Big Brown is an older male in the chimpanzee group. (Credit: John Lower)

The theory proposes that people shift their social behavior from a focus on forming new friends in young adulthood, to maintaining a smaller network of close, fulfilling relationships for companionship in old age.

“The proposal is that this shift happens because of our human ability to monitor our own personal time horizons—how much time we have left in our life—which causes us to prioritize emotionally fulfilling relationships when time is perceived to be running out,” says lead author Alexandra Rosati, professor of psychology and anthropology at the University of Michigan.

Rosati and her colleagues discovered that aging male chimpanzees have more mutual and equitable friendships characterized by high, equitable investment. Younger adult chimpanzees, in contrast, are more likely to form lopsided relationships where their partner does not reciprocate.

Older males are more likely to be alone, but also interact more with important social partners when they join the group. Males also showed a relative shift from more agonistic interactions to more positive, affiliative interactions over the lifespan, the researchers say.

“These results show that chimpanzees share these special social aging patterns with humans, even though they do not have the same rich future time perspective and knowledge of their own mortality that we have,” says co-lead author Zarin Machanda, professor of anthropology and biology at Tufts University.

The 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, she says.

The research highlights how long-term behavioral datasets from wild animals like chimpanzees can help us understand and promote healthy aging in humans, Rosati says.

Additional coauthors are from Harvard University, the University of New Mexico, and the Kibale Chimpanzee Project.

Source: University of Michigan