“Normal humans in all societies manifest a sense of sympathy: an ability to treat the interests of others as comparable to their own. Unfortunately, the size of the moral circle in which sympathy is extended is a free parameter. By default, people sympathize only with members of their own family, clan, or village, and treat anyone outside this circle as less than human. But under certain circumstances the circle can expand to other clans, tribes, races, or even species. An important way to understand moral progress, then, is to specify the triggers that prompt people to expand or contract their moral circles. It has been argued that the circle may be expanded to include people to whom one is bound by networks of reciprocal trade and interdependence, and that it may be contracted to exclude people who are seen in degrading circumstances. In each case, an understanding of nonobvious aspects of human nature reveals possible levers for humane social change.” – Steven Pinker, “Why nature & nurture won’t go away”