LAUSR

Old chimp friends As humans age, we prioritize established positive friendships over the new, but risky, socializing we do when we are young. It has been hypothesized that this shift may come as our own sense of mortality kicks in. Rosati et al. analyzed a rare, long-term dataset on social bonds among male chimpanzees and found a very similar focus on old and positive friendships (see the Perspective by Silk). Though there is evidence of some sense of time among nonhuman animals, it seems unlikely that they have the same impending sense of mortality that we experience; thus, these results suggest that a different, and deeper, mechanism may be at play. Science, this issue p. 473; see also p. 403 Male chimps focus on old friends as they age. Humans prioritize close, positive relationships during aging, and socioemotional selectivity theory proposes that this shift causally depends on capacities for thinking about personal future time horizons. To examine this theory, we tested for key elements of human social aging in longitudinal data on wild chimpanzees. Aging male chimpanzees have more mutual friendships characterized by high, equitable investment, whereas younger males have more one-sided relationships. Older males are more likely to be alone, but they also socialize more with important social partners. Further, males show a relative shift from more agonistic interactions to more positive, affiliative interactions over their life span. Our findings indicate that social selectivity can emerge in the absence of complex future-oriented cognition, and they provide an evolutionary context for patterns of social aging in humans.