A veil of ignorance can promote fairness in a mammal society

Abstract Rawls argued that fairness in human societies can be achieved if decisions about the distribution of societal rewards are made from behind a veil ignorance, which obscures personal gains result. Whether ignorance promotes animal societies, is, resources to reduce inequality, is unknown. Here we show experimentally cooperatively breeding banded mongooses, acting over kinship, allocate postnatal care way reduces inequality among offspring, manner predicted by Rawlsian model cooperation. In this society synchronized reproduction leaves adults group ignorant individual parentage their communal young. We provisioned half mothers each mongoose during pregnancy, leaving other as matched controls, thus increasing and amount variation offspring birth weight litters. After birth, fed provided extra unfed mothers, not own young, levelled up initial size inequalities equalized survival adulthood. Our findings suggest classic idea moral philosophy also applies evolution cooperation biological systems.