Throughout human history and across all human cultures, civilizations have organized themselves into social collectives, to the extent that it seems fair to say that social groups are the natural ecology of our species. In many ways, these groups play the same role as do categories in other domains; after all, the world is an incredibly complex place, and dividing it into categories is a powerful way to simplify this complexity and maximize efficiency in learning. In the social world, this way of working through complexity is especially important, given the extreme range of variability that exists across human individuals and communities. Children must navigate a world full of people with a range of properties that appear to have little in common with one another, posing a particularly difficult learnability problem. Social categorization allows children to work through this complexity by selecting features that denote meaningful differences between people (see Chapter 13). As a result, social categories become a fundamental lens through which we see the world.