That is silly. Because we know that morality can't be reduced to selfishness. Because our moral rules are against selfishness and for altruism. They are against selfishness and for the opposite. When you think about what it is that morality entails, you don't believe that morality is really about being selfish.
Morality is about being unselfish, or at least it entails that.
Which makes my point that this description, based on evolution, does not do the job. It doesn't explain what it is supposedly meant to explain. It doesn't explain morality. It is simply reduced to a promotion of selfishness which isn't morality at all. Morality is something altogether different.