If unselfish love does not extend over the whole of mankind, if it is confined within one group— a given family, tribe, nation, race, religious denomination, political party, trade union, caste, social class or any part of humanity— such in-group altruism tends to generate an out-group antagonism. And the more intense and exclusive the in-group solidarity of its member, the more unavoidable are the clashes between the group and the rest of humanity. Herein lies the tragedy of tribal altruism not extended over the whole of mankind. An exclusive love of ones own group makes its members indifferent or even aggressive towards other groups and outsiders.