Levelling: behaviours that constrain inequality in animal societies

Abstract Inequality is widespread in animal societies, with certain individuals gaining disproportionate benefits from group living. The degree of inequality varies, but little is known about its regulation. In this review, we explore the function, evolution, and mechanisms of levelling behaviours, which are actions that constrain the influence of high-powered group members and thus moderate inequality. Levelling functions by imposing costs on high-powered individuals. Evolutionary pathways to levelling depend on the costs and benefits to the levellers and the downstream consequences of reduced inequality that are shared by the whole group. Different mechanisms of levelling behaviours can lead to convergent outcomes that ultimately facilitate the maintenance of group living and drive variation in inequality across animal societies.