Sex differences innate?

I never doubted it, but here is more evidence in an informatively titled article by Christina Hoff Summers, "You Can Give a Boy a Doll, but You Can't Make Him Play With It."

One of my favorite bits:

The female preference for nurturing play and the male propensity for rough-and-tumble hold cross-culturally and even cross-species (with a few exceptions—female spotted hyenas seem to be at least as aggressive as males). 

I think that is interesting. The exceptions seem to be animals that we instinctively do not like, that we are inclined to see as reflecting some morally blameworthy quality. Of course, my impression of hyenas may be as distorted by inaccurate stereotypes as some maintain our culture's view of sexual differences are, and it may even not make sense to speak of animals as having moral behavior at all, but we associate hyenas with selfishness, opportunism, disloyalty and even cowardice. Is it, perhaps, no accident? If hyenas really are amoral creatures, really do have those character traits which popular myth ascribes to them, then I speculate that this amorality is related to their lack of sexual differences. Social animals that have no differences in abilities or inclinations have little to bind them together. They have little reason to for them to form long term bonds. They have few 'gains of trade' in Becker's sense. In a species where the sexes are no different from one another, the sexes are not bound to one another. In a species where the members are not bound to one another, there is little occasion for the qualities of self-sacrifice and loyalty that are the starting point for the qualities we call "moral".