Social bonds, social status and survival in wild baboons: a tale of two sexes

Abstract

People who are more socially integrated or have higher socio-economic status live longer. Recent studies in non-human primates show striking convergences with this human pattern: female primates with more social partners, stronger social bonds or higher dominance rank all lead longer lives. However, it remains unclear whether social environments also predict survival in male non-human primates, as it does in men. This gap persists because, in most primates, males disperse among social groups, resulting in many males who disappear with unknown fate and have unknown dates of birth. We present a Bayesian model to estimate the effects of time-varying social covariates on age-specific adult mortality in both sexes of wild baboons. We compare how the survival trajectories of both sexes are linked to social bonds and social status over the life. We find that, parallel to females, male baboons who are more strongly bonded to females have longer lifespans. However, males with higher dominance rank for their age appear to have shorter lifespans. This finding brings new understanding to the adaptive significance of heterosexual social bonds for male baboons: in addition to protecting the male's offspring from infanticide, these bonds may have direct benefits to males themselves. This article is part of the theme issue ‘Evolution of the primate ageing process'.

High social status males experience accelerated epigenetic aging in wild baboons

“…We measured cumulative adversity as a count of major adverse experiences suffered in early life, including low maternal social status, early life drought, a competing younger sibling, maternal loss, and high experienced population density (i.e., social group size). Second, we considered social bond strength in adulthood, which positively predicts longer adult lifespan in baboons, humans, and other wild social mammals [40][41][42][43] . Third, we considered dominance rank, which is a major determinant of access to mates, social partners, and other resources in baboons 40,[44][45][46] .…”

Genetic ancestry predicts male-female affiliation in a natural baboon hybrid zone

“…Males of these species may also benefit from social bonds with females. For example, baboon males who form strong social bonds with females tend to live longer than those who do not (Campos et al, 2020). Males may also benefit by gaining mating opportunities (although the evidence for this benefit is mixed), opportunities to care for their offspring, or access to infants that can be exploited for social gain (Ménard et al, 2001; Packer, 1979b; Smuts, 1985; van Schaik & Paul, 1996; Whitten, 1987).…”

“…If so, genetic ancestry effects on male-female social relationships may be more important than indicated by analyses of mating behavior alone. Specifically, because opposite-sex social affiliation also predicts lifespan in the Amboseli population (Archie et al, 2014; Campos et al, 2020), ancestry effects on this trait may secondarily affect how long individuals live and who they co-reside with, thus influencing the genetic composition of subsequent generations.…”

Insights from evolutionarily relevant models for human ageing

“…In fact, recent evidence from non-human primates indicates that social stress and ageing yield congruent physiological and molecular effects [106,107]. In this issue, Campos et al [102] report that baboons of both sexes experienced increased survival when they had strong social bonds, but as the mechanisms of social competition varied between the sexes, so did the effect of social rank on survival. However, social integration is also affected by ageing.…”

“…R. Soc. B 375: 20190605 reduced lifespan [102]. Conversely, among chimpanzees in sanctuaries, females exhibited more proatherogenic lipid profiles than males across the lifespan [98].…”