Social interactions within the family enhance the capacity for evolutionary change

Classical models of evolution seldom predict evolution in the wild. One explanation is that the social environment has important, yet overlooked, effects on how traits change in response to natural selection. We tested this idea with selection experiments on burying beetles (Nicrophorus vespilloides), sub-social insects that exhibit biparental care. Populations responded to selection for larger adults only when parents cared for their offspring, and responded to selection for smaller adults only when we prevented parents from providing care. Comparative analyses revealed a similar pattern: evolutionary increases in species size within the genusNicrophorusare associated with the obligate provision of care. Synthesising our results with previous studies, we suggest that cooperative social environments enhance the response to selection whereas conflict can prevent further directional selection.