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

People who are more socially integrated or have higher socio-economic
status live longer. Recent studies in nonhuman 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 nonhuman 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.