1. Social adaptations of this sort are really quite rare and not usually universal when they happen in human beings; for example, there are still plenty of people around who can't digest cow's milk and wheat (despite the clear evolutionary advantage to doing so post the domestication of cows and wheat), but there aren't plenty of people around who have their clitorises located in any other than roughly the normal position. In general, the sociolbiologists have better luck when they try to use biological facts to explain social ones rather than vice versa.
2. The mechanism seems way too weak to explain the biological facts. Remember that the "just so story" we're talking about here would actually go thus: "once upon a time, women had clitorises in all sorts of weird and wonderful places. But as time went on, the ones who had them conveniently located weren't able to see how much trouble their husbands were prepared to take over their pleasure, and so they tended to get married to shiftless and unsuitable men, and as a result they are extinct." It doesn't seem very likely to me.
Surely the bookies' favourite explanation would have to be that the clitoris *is* more or less conveniently positioned, if you are on all fours and copulating from behind. (You can try this experiment at home, I am told, although remember that an ape's pelvis is rather more angled than a human being's, being adapted for ape-like knuckle walking). As we developed into homo erectus, the very major morpohological changes that would have been needed to put the clitoris anywhere else (think of the plumbing!) just didn't take place, and we learned to live with it as best we could.
This also fits in with the development of the human penis, which is much bigger than that of other great apes - according to biologists of my acquaintance, this is a result of it trying to keep up with the progress of the female pelvis as it tilted further and further in the direction of upright walking, until we gave up the ghost and human beings adopted face-to-face copulation.
Eyebrows *certainly* have the purpose of keeping sweat out of your eyes; something like them are very common on basically any animal that sweats.
best dd
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