The big difference is that we're talking about species with oestrus cycles where there is a significant period of metoestrus or anoestrus between the receptive periods of oestrus. Males only harrass females in pro-oestrus or oestrus. They leave them alone the rest of the time. So the females get a break.
Human females are treated as potential mating possibilities 24/7 by human males. There is never a time when a woman can simply go about her business without the possibility of harrassment. Must be nice to be a bitch, really.
As interesting as the discussion of horse hymens is, I'd like to go back to this for a moment.
One of the other simple truths of the human condition is that because we mate all the time, not just at fertile periods, and because we don't just copulate with any available target, human females have to have a way of signaling sexual receptivity.
Needless to say, we are also the only animal where words and symbols can be a part of that signaling. Some of it is cultural. On top of that, we have a rather long term courtship compared to other species. A human female might signal availability, in a general sense, through one set of behaviors. There is another set of behaviors that might indicate to a particular male that he is a candidate for mating. Finally, a different set of behaviors signals that yes, she really does want to copulate, the sooner the better.
(Males have similar sets of behavior, although sometimes it seems that a human male indicates his willingness to mate by breathing. However, there is a different set of behaviors that indicates that he is willing to go to some effort to mate with that particular female, which seems to increase her willingness to mate with that particular male.)
Culture indicates what behaviors are associated with a willingness to mate. However, in our culture and an awful lot of other cultures, one very strong signal that a human female is ready to engage in copulation is that she takes off her clothes when a man is looking.
Of course, that can depend on circumstances. If you're in a clothing optional space, taking off your clothes does not mean that. On the other hand, I remember going to clothing optional spaces and, guess what. We were all checking each other out. And while no one was copulating at the swimming hole, there was a very significant sense of sexuality in the air, and I'm confident that after the clothes were put on when the swimming was over, they came back off in a more private setting later in the evening. (Ahh...memories, but I digress.)
The association with nudity and pending intercourse can be suppressed by cultural means, but it hasn't been. The consequence is that if a transwoman is in the locker room, a human female is now being asked to take off her clothes in the presence of a human male. That is normally a strong sexual signal. So, she's doing something associated with sexual signaling, but she is absolutely not wishing it to be a sexual signal, at all. She doesn't even know the male. All she knows about him is that he isn't very attractive, as a male, and is nonconformist in his sexual habits. And we wonder why the women aren't too keen to have this experience?
And that's on top of the fact that, if nothing else, clothing provides a physical and psychological barrier against involuntary intercourse.
Some people say that I have got it backwards when it comes to the association of nudity and intercourse. It is often said that there ought not be any connection between the two, and it is only cultural influence that makes any connection between the two. That could be true, but there are a couple of things to say about that. First, whether we are putting the cart before the horse or not, there's still a strong association between nudity and sex, and the association is deep enough that it isn't going away. Second, and related, while nudity might not be an instinctive sexual signal, I'm extremely confident that there is such a thing as sexual signaling, and in our culture, nudity is huge for that. So, regardless of the origin of the feeling, you're still asking people to do something that is a sexual signal, and then wondering why they might be anxious about it.
Furthermore, I'm not 100% convinced that the association with nudity and sexuality is completely cultural. "Common sense" would tell us that it couldn't be a product of evolutionary instinct, because our hominid ancestors didn't wear clothes. During the period when we evolved into humans, we were naked. However, humans have been wearing clothes for 100,000 years or so. That's 5,000 generations. We have no inbred, automatic way of signaling sexual receptivity the way most mammals do. I just have to wonder if concealment, and then exposure, of genitals is actually an evolved behavior as a means of signaling. Just a thought.
One final thought. We have mentioned "creepy" behavior a lot. What does that mean? I would say that for the most part it consists of people not noticing, or not caring about, the sexual receptivity signals. In other words, a guy is hitting on a girl that is clearly sending out "No" vibes, but the guy either doesn't know, or doesn't care.
