Older chimpanzees accentuate the positive

A new KCP study published in Science shows that wild chimpanzees share social aging patterns with humans, by prioritizing strong social bonds and interacting with others in increasingly positive ways as they get older. 

KCP researchers led by Dr. Alex Rosati and Dr. Zarin Machanda leveraged our exceptional long-term dataset to test socioemotional selectivity theory – an influential idea in psychology aimed at explaining why humans show changes in social interactions during aging. Socioemotional selectivity 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.

Using 20 years of behavioral data, researchers found that chimpanzees, like humans, increasingly prioritized mutual and equitable friendships with others that invested in them as they got older. Younger adults, in contrast, were more likely to form lopsided relationships where their partner did not reciprocate. Older chimpanzees also were more likely to be seen alone, but tended to socialize more with important partners when they did join the group. Finally, they showed a positivity bias in their overall behavior: reducing their aggressive behavior while maintaining levels of affiliative grooming. 

Taken together, 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. This is the first demonstration that a nonhuman shares these characteristics with us. 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. This research highlights how long-term behavioral datasets from wild animals like chimpanzees can help us understand and promote healthy aging in humans. 

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