Historically, cities usually had R < 1. Cities were unhealthy places, and the urban poor had fewer opportunities to provide for their children than the rural po

Historically, cities usually had R < 1. Cities were unhealthy places, and the urban poor had fewer opportunities to provide for their children than the rural poor. Regardless, people continued to migrate to cities for economic opportunities, and cities were the places where social and cultural developments happened. Parents passing their values to their children does not seem to be the right model. Children choosing from the available opportunities is a bit better. Groups with high fertility rates tend to export people, because there is not enough room for the excess children in their ancestral culture. The ones who leave tend to be the ones who did not fit into the culture anyway, and they often adopt new values and a new way of life.