A few times now I've mentioned my new found interest in biological evolution, particularly human evolution. This doesn't mean, however, that I've become an atheist which many believe (including both theologians and prominent evolutionary biologists) is requisite for belief in evolution, at least human evolution. No, I remain a theist and I don't believe these positions are mutually exclusive. But I just as strongly do not think any version(s) of "intelligent design" or ID should become a regular part of any public school's science curriculum (which is sadly where my State appears to be headed).
Nevertheless, in a sort of half jest I've pointed out to some of my ID friends that there are certain oddities with human physiology that appear to defy satisfactory explanation from an evolutionary perspective, thus perhaps directly pointing to an intelligent designer. My favorite one to reference is the clitoris: the seat of female orgasm. Now since time immemorial women have known that the chief area of stimulation for them to reach orgasm lies at/in their clitoris (unfortunately some men come upon this revelation much too late to the chagrin of their female mates). And though some women can achieve orgasm through vaginal intercourse most can only do so through direct or at least indirect stimulation of the clitoris. Furthermore, many studies have borne this out over the last half century or so. (Since I'm sure the majority of women can personally attest to what I've just said it may seem a bit odd that I'm about to back my claims with some scientific studies but hey I'm trying to be as academic about this topic as possible.)
There are three in particular worth mentioning briefly here. First, there was the Kinsey report of 1953, one of the first academic studies (aside from some of the eccentric studies done by Freud) dealing with human sexuality. In the volume released that dealt with female sexuality it reported that out of a sample of 8,000 women only about 15 percent could reach orgasm through means other than clitoral stimulation whether during masturbation and/or sexual intercourse. Likewise, Masters and Johnson's book of 1966 had similar results in its study and concluded that "female orgasms are identical in physiology and clitoral in origin." And lastly The Hite Report of 1976 found that out of a sample of 3,000 women less than 25 percent could reach orgasm without at least indirect stimulation of the clitoris leading Shere Hite to conclude that "not to have orgasm from intercourse is the experience of the majority of women."
But what bearing does any of this have on evolution and intelligent design? Well, if one assumes that evolution occurs because of the utility of a newly evolved trait (and its subsequent replication in a species) then the existence of the clitoris seems problematic for the theory of evolution. To make sense of this argument let's consider the reproductive organ of males: the penis. The evolution of the penis makes sense because the peak of sexual excitement in a male occurs during ejaculation which of course usually takes place during vaginal intercourse that then leads (usually) to the further propagation of the species. In other words on an evolutionary account the appearance and development of the penis makes perfect sense because of the immediate and direct function it has in promoting the continuation of a species. However, the same cannot be said for the clitoris because it doesn't appear to perform any direct function in the reproduction of the species. Another way to think about this is that one would expect the interior of the vagina to be the primary site of female orgasm because that is the site of reproduction but as mentioned above it clearly isn't. To the contrary, the clitoris is decidedly away from the primary site for reproduction. In a nutshell, the existence of the clitoris is difficult to explain on the basis of evolutionary theory because it doesn't appear to have a basis in utility. Thus, the origin of my half jest that all one need do is point to the clitoris as proof of God's existence.
Of course when you think you've hit upon an original insight it is almost always the case that someone else had already done so long before you did. And that was the case here because a couple of weeks ago I stumbled upon this very issue in an essay by the late paleo-biologist Stephen Jay Gould entitled "Male Nipples and Clitoral Ripples" (it can be found in a collection of natural history essays by Gould in Bully for Brontosaurus). In this essay he deals with the difficulty in explaining male nipples and, for our purposes, the clitoris in terms of evolution. (For those curious about male nipples I would encourage you to read the essay though as you will see in a moment the solution to this puzzle is the same for both) And to my surprise he offers what I think is a very satisfactory account for the evolution of the clitoris.
But before revealing this explanation it's best to point out a misunderstanding (or perhaps, better, incomplete understanding) many have about how evolution works (this included me until reading Gould's essay). This "incomplete" grasp of evolution has to do with what I stated above, namely, the belief that a trait/characteristic evolves solely because it performs some sort of direct function for a species. In other words, the explanation for why a certain trait/characteristic evolved and developed must necessarily be for an adaptive purpose. Or as Gould puts it, "many are committed to a 'pop' form of Darwinianism that adopts a principle of pervasive utility for all parts of all creatures." (126)
However, as Gould notes a proper, holistic grasp of evolutionary theory holds that traits in an organism can also evolve for "structural nonadaptive" reasons, i.e, evolution may produce a structure in an organism that at least initially doesn't serve any purpose. And as Gould emphasizes in his essay modern evolutionary theory operates from a synthesis of both functional and structural perspectives.
With this in mind the explanation for the evolution of the clitoris is actually rather simple and has to do with a structure produced by evolution, namely, the human embryo. Perhaps it's best to just let Gould elaborate at this point:
"Both sexes are variants upon a single ground plan, elaborated in later embryology...the external differences between male and female develop gradually from an early embryo so generalized that its sex cannot be easily determined. The clitoris and the penis are one and the same organ, identical in early form, but later enlarged in male fetuses through the action of testosterone." (127)
"The reason for a clitoral site of orgasm is simple...the clitoris is the homologue of the penis-it is the same organ, endowed with the same anatomical organization and capacity of response." (129)
So then the clitoris and the penis are homologous structures and it is through subsequent sexual differentiation that the reproductive organs of the respective sexes appear; evolution having produced this structure or "ground plan" in the human organism. And there you have it: a satisfactory, evolutionary account of the origins of the clitoris. Sorry ID friends but I'm afraid that the clitoris is no longer proof that God exists.
*Note: the solution for male nipples is the same: the result of sexual differentiation from homologous structures. Also, Gould does note a few who actually try to account for the evolution of the clitoris from a purely adaptive perspective (e.g., as a means of pair bonding). He also takes on some of the ridiculous arguments of Freud concerning human female sexuality. For those interested I would encourage you to read the entire essay.