They have morals because they feel an intense desire, like religious people, to build a better society for themselves and their children. According to them, this desire has an evolutionary origin, because people who feel this desire will contribute to a good, functioning society. A good functioning society will lead to prosperity for all of its members and will therefore result in reproductive success. This reproductive success will result in future generations who share the same DNA with their parents and therefore have the same desire to be moral.