the cultural evolution of creative new societies requires more elbow-room than a single planet can provide. Creative new societies need room to take risks and make mistakes, far enough away to be effectively isolated from their neighbors. Life must spread far afield to continue the processes of genetic drift and diversification of species that drove evolution in the past. The restless wandering that pulled our species out of Africa to explore the Earth will continue to pull us beyond the Earth, as far as our technology can reach.