On Cultural Relativism and Rape

Christian philosopher Victor Reppert offered up an argument against condemning rape if cultural relativism is the case. He wrote:
I had a teacher at Arizona State who told me that in one culture rape is considered perfectly OK, so long as you do it at the right time. In the morning, it's forbidden. In the afternoon, it is frowned upon. At night, it is perfectly OK, since a woman who is away from the protection of her husband is asking for it. (He never said which campus fraternity he was referring to).

If cultural relativism is true, the rules of that culture, with respect to rape, are justified. There is no "court of appeal" that is over and above that culture and out culture that would permit us to say that their views on rape are wrong and ours are right. For us to suggest that they are "really" wrong in permitting rape is to elevate the rules of our culture to a kind of cosmic status they cannot have. It is to be intolerant.
This is my brief response:

Let's say morals evolve in the same way as species do. Grant me that, okay?

Then I don't see a problem. The caveman who clubbed a woman and drug her into his cave did nothing wrong just as a chimpanzee who exhibits homosexual activity, or a dominant lion who demands sex with all of the females, or a cat who shows no mercy to a mouse.

We humans adopt codes of conduct in order to have the benefits that our higher species need, like friendship, family ties, and so on. That best explains why our moral codes are similar around the world on the major, basic issues, and why they are diverse on the moderate, lesser issues.

So, in a caveman culture rape is considered right. But in ours it is not. Our culture is different. Is it better? I would argue so, at least from our evolutionary standpoint. It's because we have continued to evolve. Because we do our morals have evolved in tandum.

Besides, it's not relativists who argue for rape, anyway, it's religious people, like what we find in Muslim and Old Testament texts.