Parental care allows genetic variation to accumulate by relaxing selection

Benign social environments are thought to relax selection against deleterious mutations, enabling them to accumulate in the genome. However, it has not proved straightforward to demonstrate causality in this relationship. We allowed burying beetle populations to evolve with and without the benign effects of parental care for over 20 generations, before inbreeding lineages that were seeded from these experimental populations to expose any differences in their mutation load. We found that inbred lineages with a history of parental care went extinct most quickly, indicating that they harboured more recessive deleterious alleles.