<p>Across species, a major axis of variation in social behaviour relates to how offspring are reared. Parental care behaviours have independently evolved in hundreds of animal lineages. Care is usually limited to one or both parents, but in some lineages parenting is a highly cooperative endeavour. In social insects, for example, entire societies have evolved around parenting, complete with distinct adult morphs that specialize in reproduction, nursing, foraging and defence. Recent advances in omic technologies have enabled data collection across diverse taxa, revealing broad patterns in the molecular regulation of parental behaviour. These studies indicate that evolution has systematically co-opted molecular machinery that pleiotropically regulates three deeply interlinked biological processes: feeding, growth and reproduction. Where more sophisticated social systems have evolved, the same factors have been further co-opted to additionally regulate the developmental differentiation of distinct morphs, division of labour between adults and behavioural changes associated with ageing. These findings suggest that complex behaviours evolve through repeated and predictable co-option of ancient molecular systems.</p>