The fittest being those who treat others as they wish to be treated themselves. Morals don't come from God. Even if you are willing to accept that God doesn't exist, you still live by a set of morals. Morals come from our individual values. Assuming our highest value is our own individual survival, we will avoid doing anything that may jeopardize it. We treat others fairly because life is harder if we don't. Treating others unfairly limits our ability to eat well. Simple as that. God has nothing to do with it other than that God serves the same purpose for adults that Santa Clause serves for children.