To exploit ecological niches where constraints have favoured selection for group living and cooperation, both vertebrates and invertebrates have evolved elaborate social systems. In mammals, numerous divergent taxa have converged at similar solutions to these ecological challenges (such as food distribution and predator avoidance), culminating in the social insect-like behaviour of the naked mole-rat. Characteristically, breeding is partitioned unequally in such groups, resulting in a 'reproductive skew'. New research linking studies of physiology, behaviour and molecular ecology in African mole-rats is helping us to elucidate why different proximate mechanisms that control groups of cooperative breeders might have evolved.