Kanyawara Chimpanzee Male: Big Brown is an older male in the group. Image credit: John Lower

Humans prioritize close, positive relationships during aging, which can support physical and mental health.

But these social aging behaviors are also found in wild chimpanzees, who seek interactions with other group members in increasingly positive ways as they get older, according to a new study published in Science Oct. 23.

The work—led by researchers at the University of Michigan, Tufts University, Harvard University and the University of New Mexico—uses data from the Kanyawara chimpanzee community living in Kibale National Park in Uganda. The animals have been studied for decades by the Kibale Chimpanzee Project, and researchers used this long-term dataset to test socioemotional selectivity theory.

Dyad of Kanyawara Chimpanzees Grooming: Stout, an older male (on left) grooms Big
Brown (on right), another old male who is his long-term mutual friend. Image credit: Ronan
Donovan.

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 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,” said Alexandra Rosati, U-M professor of psychology and anthropology and the study’s lead author.

Rosati and 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,” said Zarin Machanda, professor of anthropology and biology at Tufts University and the study’s co-lead author.

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). Image credit: John Lower.

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 said.

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

The study’s co-authors are Lindsey Hagberg and Richard Wrangham, researchers at Harvard University; Drew Enigk, Melissa Emery Thompson and Martin Muller, researchers at the University of New Mexico; and Emily Otali, field director of the Kibale Chimpanzee Project.

More information:

• Study abstract: Social selectivity in aging wild chimpanzees
• Alexandra Rosati