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'.
Highlights
Sociologists have long known that social integration [1,2] and socio-economic status [3,4] are among the most powerful predictors of mortality risk in humans
Similar strong relationships between lifespan and social environments have been revealed in primates [5,6,7,8,9,10,11,12,13], hyraxes [14], ungulates [15,16], whales [17,18], rodents [19], carnivores [20] and lagomorphs [21]
It remains unclear to what extent strong social bonds and high social status enhance longevity in male non-human primates, as they do in men [1,2,4,29,30]
Summary
Sociologists have long known that social integration [1,2] and socio-economic status [3,4] are among the most powerful predictors of mortality risk in humans. In long-lived iteroparous mammals, empirical and theoretical work indicates that lifespan is the most important component of Darwinian fitness in both males and females [24,25] In spite of this fact, the relationship between social environments and survival in male mammals remains understudied. We present a Bayesian model that enabled us to include time-varying covariates of social bond strength and social status (dominance rank) in estimating age-specific mortality in wild male and female baboons (Papio cynocephalus). We apply this model to an unprecedented dataset spanning 35 years of longitudinal life-history data and fine-grained observations of social environments for 265 adult female and 277 adult male baboons in Amboseli, Kenya. Our results contribute to a growing body of evidence that takes advantage of non-human primate studies to shed light on physiological, reproductive and actuarial senescence in humans, and on the evolution of lifespan [31,32,33,34,35,36,37]
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