Group size and social rank predict inhibitory control in spotted hyaenas

Abstract

Inhibitory control is the ability to resist performing a prepotent, but ultimately incorrect, behaviour in situations that demand restraint. Inhibitory control is linked to brain size and intelligence in humans and animals, but it is unclear just how it evolves. Inhibitory control is thought to be particularly important in complex social environments where demands can shift frequently based on the social context and the identities or behaviours of other individuals in a group. Indeed, the social intelligence hypothesis suggests that the demands of living in complex social groups led to the evolution of sophisticated cognition. Here, we tested inhibitory control in wild spotted hyaenas, Crocuta crocuta, whose large social groups are structured by linear dominance hierarchies. We tested inhibitory control using the cylinder test, which requires subjects to inhibit going straight for a food reward. In support of our predictions, hyaenas living in larger groups had greater inhibitory control. In particular, the size of the cohort in which young hyaenas grew up, rather than the size of adult groups, had the strongest effect. In addition, the effect of group size was significantly stronger for low-ranking hyaenas, which must frequently inhibit both feeding and aggression in the presence of higher-ranking hyaenas. Contrary to our predictions, adult male hyaenas, which always occupy very low rank positions as adults, did not have better inhibitory control than adult females. This suggests that inhibition is not a canalized trait, but instead may be a flexible one such that its development is influenced by early life social environments.