Scientists have long gotten used to the idea that bodies are just genes’ ways of making more genes, survival machines that carry genes to the next generation. Think of a salmon struggling upstream just to expend its body (now expendable) in spawning. Evolutionary biologist Mark Pagel’s idea is that cultures are an extension of this: that the way we use culture is to promote the long-term interests of our genes.

When human beings’ lives became dominated by culture, they could have adopted habits that did not lead to having more descendants. But on the whole we did not; we set about using culture to favor survival of those like us at the expense of other groups, using religion, warfare, cooperation and social allegiance. What this means, Pagel argues, is that if our “cultures have promoted our genetic interests throughout our history,” then our “particular culture is not for us, but for our genes.” We’re expendable. The allegiance we feel to one tribe—religious, sporting, political, linguistic, even racial—is a peculiar mixture of altruism toward the group and hostility to other groups. Throughout history, united groups have stood, while divided ones fell.