People frequently speak about how divided the United States is right now. This comment is often associated with things like left-wing protests on college campuses, discussions of partisan media, and gridlock in Washington DC. This divisiveness is frequently attributed to “tribalism.” But “tribalism” doesn’t strike me as a very informative explanation. It is merely a description of the effect but, doesn’t say a lot about the cause. The question then is, what makes our society more or less tribal...