Social selectivity in aging wild chimpanzees

Abstract

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.

Age-related change in adult chimpanzee social network integration

“…2). Their selective focus parallels other findings from this field site using different measures of sociality, where males formed more equitable relationships with one another as they aged (Rosati et al, 2020). However, in this analysis, the effects of aging on cliquishness (grooming transitivity) and overt social effort (outdegree) were most affected by decreased interactions with females, as these two dimensions changed in mixed-sex but not in all-male networks.…”

“…To contribute to this goal, our present study examines patterns of social aging using a mixed-longitudinal behavioral dataset from one of our closest evolutionary relatives, wild chimpanzees. Although human and chimpanzee social worlds differ, recent evidence shows that male chimpanzees exhibit striking similarities to humans in how their dyadic friendships change with age (Rosati et al, 2020). We expand on work from Rosati et al (2020), by evaluating several life-history based drivers of social aging, and characterize multiple dimensions of sociality using a suite of social network integration measures in both males and females (Table 1 & Supplement).…”

“…Humans, however, are not the only animals that exhibit decreased social integration with age (e.g. red deer, Albery et al, 2021;macaques, capuchins, lemurs, reviewed in Machanda & Rosati, 2020;yellow-bellied marmots, Wey & Blumstein, 2010), and chimpanzees exhibit a suite of features associated with human social aging, including a positivity bias and strengthening of close friendships Rosati et al, 2020). Thus, valid interpretations of social aging require a more generalizable framework, such as that offered by life history theory.…”

Cofeeding tolerance in chimpanzees depends on group composition: A longitudinal study across four communities

“…Certain aspects of chimpanzee sociality are known to be temporally stable; for example, dyadic relationships can be maintained over many years ( Gilby and Wrangham, 2008 ; Kossi et al., 2012 ; Langergraber et al., 2009 ; Rosati et al., 2020 ), as can some alpha male tenures ( Goodall, 1986 ). It is unclear, however, to which extent this stability extends to group-level social styles.…”

How long‐term studies reveal otherwise hidden phenomena: The Long‐Term Animal Research Seminar Series

“…Long‐term datasets capture within‐individual longitudinal processes including senescence, lifetime reproductive success, and links between life history stages that are difficult to assess from cross‐sectional studies. Zarin Machanda used 78,000 hr of observational data collected over 22 years to show that older male chimpanzees ( Pan troglodytes ) were less aggressive and had more mutual friendships than younger males 7 . This work has implications for our understanding of the evolutionary origins of social aging in humans, which follows a similar pattern.…”