Figure 1.

Mechanisms of equality and inequality in animals. Among the many examples in nature: (a) ravens co-feed with non-kin, are averse to inequity and reconcile after fights, (b) African wild dogs share food even with adults and adopt young born to others, (c) capuchins share food and are averse to inequity, (d) chimpanzees inherit tool sites and forgive each other after fights, (e) naked mole rat queens dominate reproduction within their unequal societies, (f) killer whales share food and knowledge, and (g) spotted hyaenas inherit social status and land within family lineages. Photographs reproduced via Creative Commons Licence or permission: (a) Stephan Dickson, (c) Frans de Waal, (d) (copyright: the Jane Goodall Institute)/by Fernando Turmo, (f) Callan Carpenter and (g) Bernard Dupont.