Breeding in large, cooperative groups allows the costs of reproduction to be shared amongst individuals. This has enabled organisms to live in places that would otherwise be uninhabitable. However, a ubiquitous feature of animal societies is that breeding groups vary markedly in their size and composition. Why, given the benefits of cooperation, do large groups only sometimes emerge? Here I present a series of experiments on the worlds largest bird, the ostrich, where the answer to this question involves a tale of sex, cheating and cooperation in the struggle to reproduce in some of the hottest places on earth.