Like humans, wild chimpanzees focus on fewer yet more meaningful friendships as they grow older, say researchers who studied male chimps over two decades. Their study, a test of an influential psychological theory that attributes aging humans' social life changes to a sense of limited future time, provides the first evidence that nonhumans exhibit age-related social selectivity, too. Socioemotional selectivity theory (SST) suggests that people prioritize established and positive relationships more as they grow older because of their own impending sense of mortality, preferring to spend time with their closest, oldest and most important friends rather than in making new ones. While this inclination is widely observed across humans, who are assumed to exhibit unique complex reasoning about the future, evaluating whether an explicit sense of future personal time drives this behavior isn't easy; some recent evidence also suggests changes in socioemotional goals as people age can be independent of future time perspective. Here, taking advantage of the way comparative studies of humans and other social animals can inform human social behavior and its origins, Alexandra Rosati and colleagues tested whether key elements of human social aging are shared with wild chimpanzees. Using a study done over two decades in Kibale National Park, Uganda, the authors report on social interactions among 21 wild male chimps, ranging in age from 15 to 58 years. According to the findings, aging male chimps have more mutual and positive friendships than younger chimps, who had more one-sided, antagonistic relationships. And although they are more likely to be alone, older chimpanzees also socialize more with important social partners. The results show that increasing social selectivity can occur in the absence of a rich future time perspective, the authors say. "Thus, the patterns that SST was created to explain appear to generalize beyond our own species and might not depend on having a well-developed concept of time or conscious awareness of mortality," writes Joan Silk in a related Perspective.
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Journal
Science