The co‐evolution of longevity and social life

Living in social groups could influence the evolution of senescence and longevity by affecting key life‐history parameters such as extrinsic mortality and the cost of reproduction. For example, a decrease in extrinsic mortality as a result of social life is predicted to lead to the evolution of increased longevity. We argue that benefits of social life in terms of increased survival are common only in species in which life in large groups is already the norm, most likely because these species have adapted to depend on social groups. By contrast, species with smaller social groups tend to show no clear association between survival and social group size. This lack of a consistent benefit of social life on survival casts doubt on the idea that extended longevity should follow the evolution of sociality. In line with this, most rigorous cross‐taxonomic studies failed to find an association between sociality and longevity, suggesting that a social mode of life does not systematically lead to the evolution of extended longevity. The only effect of sociality on longevity that has been convincingly demonstrated is increased longevity in high‐ranking individuals from cooperatively breeding vertebrates and social insects, who benefit from the protection and support of their non‐breeding helpers. In contrast, helpers in these species usually do not show evidence of increased longevity, with the exception of naked mole rats where both breeders and helpers live much longer than related solitary species. Where long‐lived phenotypes exist in highly social species, such as social insect queens and naked mole rats, the scale of longevity increase is often striking. The means by which increased longevity is achieved are still poorly understood, but both social and physiological mechanisms are involved in reducing the burden of disease, including cancer, thus increasing the chances of surviving to old age