Psychologist Muzafer Sherif and colleagues created an experiment that demonstrated just how quickly we form alliances within a group against another group and how seriously we take these group differences. The experiment involved 3-week-long group experiences for 11- and 12-year-old boys at campsites in Oklahoma. The boys were initially grouped together and allowed to choose friends freely. Then, the boys were split into two groups: For each boy, about one-third of the new group-mates were part of their old friend networks and two-thirds were new. In a week, the boys changed their friendships so that most of their friends now came from the current group. More dramatically, when the boys engaged in a sports tournament, sportsmanship declined, and the boys ended up in aggressive, angry competition, including physical fighting. Competition was eliminated only after the two groups were asked to work cooperatively on a task of mutual interest (i.e., a superordinate goal).