Abstract: Cultures and religions have produced major benefits for billions of people, mutilations of billions of people and deaths of millions. The most reasonable and parsimonious interpretation of these disparate phenomena starts with human nature. Humans, like other social mammals have an innate inclination to form exclusive cooperative groups that have conflicts with other groups of their own species and have restricted participation in reproduction. Cultures and religions provide identification of the members of a group. Cultures and religions are identifying behaviors, like passwords. They allow the development of very large groups.