There are certainly facts of how morality evolved, but the reason there's an is-ought problem is because there's another relevant fact: the prescriptions don't follow logically from any set of descriptions, including a description of how we evolved. So it doesn't follow that just because some trait is useful for an evolution purpose, we morally ought to use that trait. You mean to reduce morality to evolutionary functionality, whereas morality developed as a challenge to our evolutionary heritage, when we became "behaviourally modern," that is, when we invented culture around 200,000 years ago.

Rape may have had an evolutionary function, as it does in many species because the female's feelings are irrelevant to the genes, and what matters is the alpha's dominance which keeps the group together and which allows that leader to transmit the group's best genes to the next generation. If morality is the same as evolutionary functionality, then the function of rape would be the same as its moral value. But again, morality emerged later as a cultural reflection on what's right. Evolution may have influenced those reflections, as did our imagination, dreams, and even our delusions (such as religious ones). But when we arrive at the Western tradition, we find that morality has become an autonomous discourse, just as sciences which begin as philosophy become autonomous disciplines.