The minimum group paradigm is a methodology In social psychology most commonly used to investigate the minimum conditions required for discrimination to occur between groups. The most trivial of distinctions, such as eye colour, reveal the propensity in humans to form an in-group bias.
The tendency to favour one’s own group, even a group formed over something as arbitrary as shirt colour, will manifest itself to the degree that this favouritism at the expense of others is actually unproductive for oneself. In studies in which groups are created and offered money a zero sum mentality is reflected by a group preference to maximise difference between groups rather than the amount their group receives.
Sam Bowles used mathematical models to show that conflict between groups for scarce resources was a necessary ingredient in our evolution for the emergence of altruism within groups.
The only similarly divisive species is the chimpanzee which gives weight to the idea that kindness and hatred are intertwined. Models show that the past conditions were ripe for both altruism and ethnocentrism, but only when both were present.