Our 'Tribalistic Tendencies'

"Humans originated by multilevel selection—individual selection interacting with group selection, or tribe competing against tribe," says sociobiologist E.O. Wilson (The Social Conquest of Earth) in an interview. He contends that this explains why we humans are rocked by conflicting emotions, such as selflessness vs. selfishness, and why "we never seem to be able to work things out satisfactorily, particularly internationally": http://www.slate.com/articles/health_and_science/new_scientist/2012/04/e_o_wilson_on_altruism_and_the_new_enlightenment.html