A very interesting theory to contemplate. I feel this helps make sense of our current state of tribalism and morality.

Territorial violence might have been necessary for development of altruism. The economist Samuel Bowles has argued that lethal, “out-group” hostility and “in-group” altruism are two sides of the same coin. His computer models suggest that altruism cannot emerge without some level of conflict between groups. If true, this is one of the many places where we must transcend evolutionary pressures through reason – because, barring an attack from outer space, we now lack of proper “out-group” to inspire us to further altruism.

Sam Harris

Explains why it seems that we are constantly looking for a “they”, “them”, or “other” to transgress upon, contradictory to the altruism we show “our” own group.