We can cooperate more easily with those who more easily intelligible to us, who are more familiar to us. But the advantages of specialization of labor often push us in the direction working with people who have different strengths and viewpoints than we do. I think that this is one major reason why moralities are always subject to change, because some of the people we cooperate with are going to be different from us in ways that often lead them to have different value orientations than we have; and interacting with them can change us.