How we view and treat “the Other” is very important to human behavior. Much violence (whether war or between individuals) derives from antagonism between groups. We evolved, back when humans lived in small bands of hunter-gatherers, to feel part of the group of people we see around us and are familiar with, and to feel caution or antagonism toward other groups. That attitude protected us in our prehistoric social environment. But we inherited those same instincts although there’s been a drastic change in our population, both in number and organization. Dealing with the clash between our grouping instinct and the widespread contact and mixing of groups is a constant challenge, just as we need to deal somehow with the conflict between modern society and other ancient instincts (for example: the modern abundance of food vs. our craving for fat and sugar). To adapt, we should remember the instinct is present, study it, and test ways to live together happily and successfully.