For most of human history, people were hunter-gatherers. They lived in large camps, depending on one another for food, childcare, and everything else—all without walls, doors, or picket fences. In comparison, the number of people living in most households in today’s developed countries is quite small. According to the Census Bureau, fewer than three people lived in the average American household in 2010. The members of most American households can be counted on one hand, or even, increasingly, one finger: Single-person households only made up about 13 percent of all American households in 1960. Now, that figure is about 28 percent.