Why do Woman ... Well, you'll see.

It's often been asked, evolutionarily speaking (it's a harder question for a creationist, though) why do male mammals, including ourselves of course, have nipples?  No functional purpose can be assigned to them so you think natural selection would "prefer" males who don't.  I think there's an even better question however:  why do female mammals have a clitoris?

The answer is clearly not for pleasure.  First, nature doesn't give a hoot about pleasure in making its choices.  Second, outside of humans and some other mammals, females don't enjoy sex at all (just watch two cats at it; she's clearly in pain and drives him off as quickly as they have intercourse).  She's driven by hormonal changes and attracts males to mate to her.  So why do they have an organ of pleasure if they don't use or need it?

I think the late, famous paleontologist Stephen Jay Gould would have the answer to this.  It isn't known exactly when (pre?) mammalian genitalia evolved (maybe as much as 200-250 million years ago, or much more recently), but they probably evolved from their reptilian ancestors who used a "primitive" cloaca system (everything comes out one tube) -- a system still basically in use by most modern reptiles and birds.  One of Gould's basic themes in his life is the natural selection is not all-powerful; it can't sculpt living this to exact specifications or proportions.  In a sense this is obvious (despite Richard Dawkin's ill-deserved reputation for "claiming" otherwise); natural selection can only work on gene selection, and most genes don't do just one thing -- we have about 20-25,000 genes and these interact in the body of the embryo/fetus/child and the physical and chemical environment of the womb to form all the millions of individual features we possess.

Here's the trick with we mammals.  As very young embryos we are all females; the basic genitalia and internal sex organs all develop within the abdomen.  No doubt the nerves that lead to sexual arousal and please largely develop then too, and have been since the beginning.  Why?  We'll probably never know because soft tissues are rarely fossilize -- we can make intelligent guesses about it (same about why not in reptiles and birds), but that's about all.

There is a gene, dubbed SRY, on the Y chromosome (which, recall, only males have; females are XX) which at several weeks into gestation, becomes active and causes the release of testosterone in the male body.  This causes a number of physical and chemical changes.  One of these changes is the decent of the proto-penis and testicles downward, into their position when he is born.  Prior to this however, the progenitor of the penis exists in both sexes; in females it descends too.  In other words, the penis and the clitoris start off as the same structure, already equipped with sexual nerves.  There probably aren't any available mutations that would eliminate the clitoris or its sexual nerves (genes to many things, remember) so natural selection cannot achieve this.  The net result as that as least some female mammals (and potentially perhaps all of them) get to enjoy this accidental benefit.  But accident is just what it is.