The human tendency to gravitate towards people that are similar to them starts early. In school-age children, the behavior called homophily, or "love of the same" often has to do with how others dress or act. Adults tend to form groups based on social stature, professions or personalities. Turns out that forming cliques and shutting out those that are "different" is not just a human trait. South Africa's Chacma or Cape baboons display similar tendencies as well!