The most basic community of humans is the family. Multiple families working together form a tribe. Tribes can gather together to form larger communities — clans, city-states and nations. This is, in a general sense, the pattern of human civilization. But the family remains the basic unit, and because humans are animals too, we are also subject to kin selection, an instinctive desire to support family members over unrelated people, no matter how big or powerful our larger communities become.