Female gregariousness is a hallmark of elephants and many social mammals. This chapter examines the ecological and evolutionary explanations for sociality among elephants. Social life comes with costs (competition, subordination) and benefits (protection, knowledge) that differ across ecological contexts. The fundamental selective pressures and trade-offs represented by varied resource distributions and predation or hunting risks are discussed, taking pains to differentiate between species and populations. The influence of seasonality on resource availability, and in turn on fission-fusion dynamics and dominance interactions, provides a rich space of possible social interactions at multiple levels of organization and complexity. Disruptions to elephant societies, either because of deaths or management interventions, provide insights into both the fragilities and resilience of their social systems.

Examining variation in social behaviour and associated endocrine physiology across groups of the same species can help identify consistent hormone–behaviour interactions. We investigated differences in urinary oxytocin levels of individuals, of two neighbouring chimpanzee groups related to (a) socio-positive and -negative interaction frequencies, (b) within-group cooperation associated with between-group competition and (c) group-specific differences in urinary oxytocin reactivity of individuals in response to the same behavioural contexts. We found higher rates of cooperative group-level behaviours and larger relative party sizes in East Group males, while South Group males had higher non-directed aggression and copulation rates. Individuals of both groups showed consistent urinary oxytocin reactivity after the same behavioural contexts. However, East Group males had higher urinary oxytocin levels across contexts than South Group males, including higher baseline levels. Our results support the oxytocinergic system’s involvement in cooperation and gregariousness, and suggest an association between group-specific social dynamics and oxytocinergic profiles.