Humans are able to cooperate with others in sophisticated, flexible ways: assisting others who need help, working collaboratively in teams, and sharing resources according to what’s ‘fair’. How do humans accomplish these behaviors? In some views, we are initially driven by purely selfish motives and must be taught to be cooperative. Yet other views suggest we have a biological predisposition for cooperation that emerges early in childhood. I will discuss developmental studies with children and comparative studies with chimpanzees that provide insight into the origins of human evolution and development.