As scientists apply our new understanding of the human genome to genetics, we’re getting answers to big-picture questions about our species. What is race? How did humanity spread around the globe? How should we pick a mate (genetically speaking)? We talk with Adam Rutherford, geneticist and author of “A Brief History of Everyone Who Ever Lived: The Human Story Retold Through Our Genes,” about the history of our genes, and what they reveal about our species.