Aging chimpanzees and aging humans: not that far apart

As humans and chimpanzees age, they exhibit similar patterns of social behavior. Aging behavior in humans was thought to be based on the ability to realize and understand that our lives were drawing to a close. But, that may not be the case. The similarities between aging humans and aging chimpanzees may point to a deeper evolutionary mechanism.

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*Rosati, A. G., Hagberg, L., Enigk, D. K., Otali, E., Emery Thompson, M., Muller, M. N., . . . Machanda, Z. P. (2020). Social selectivity in aging wild chimpanzees. Science, 370(6515), 473-476. [PDF] [Cited by]

“Social bonds have adaptive consequences over the lifespan: strong social support enhances health, longevity, and biological fitness.”

“As humans age, we prioritize established positive friendships over the new, but risky, socializing we do when we are young. Older adults across societies have smaller yet more emotionally-fulfilling social networks than younger adults” (due to the increasing focus on existing close relationships). “Older adults [also] exhibit a positivity bias, showing greater attention to and memory for positive versus negative socioemotional information, and reduced engagement in tension and conflicts.”

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” [that is, thinking about our mortality]. “To examine this theory, we test for key elements of human social aging in longitudinal data on wild chimpanzees.” Similar to humans, “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 also socialize more with important social partners. Finally, males show a relative shift from more agonistic interactions to more positive, affiliative interactions over the lifespan. Our findings indicate that social selectivity can emerge in the absence of complex future-oriented cognition, and provide an evolutionary context for patterns of social aging in humans.” There is something deeper going on …

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