Well, my husband Mike has been on me for quite a while now to have me add something to the blog. So here goes.
On a long drive home form Oregon a couple of weeks ago, I started thinking about a couple of evolutionary issues. I'd heard some explanations for them, but I wasn't convinced that they were good ones. I had a lot of time to think and develop my own theories, so I could research them when I got home. I haven't finished my work on these theories, but as a favor to Mike I'll post a bit about them now, and more later when I finish my research.
So these were the questions that struck me. Why do human males have such large penises? And what, if anything, is the evolutionary significance of female orgasm?
As to the first question- human males have penises that are much larger than one would expect for animals of our size- about 5 3/4 inches. The male gorilla, by contrast, is three times larger but is gifted with only three inches. Why are human males so well-endowed?
As to the second- if orgasm serves any useful evolutionary function in females, what could it be and why has selection for it been so weak? The majority of human females cannot reach orgasm through intercourse alone, and many women never reach orgasm through any means.
So, the theories that I came up with were these.
As far as the male penis, I theorized it evolved much as the antlers of a deer- to serve as an advertisement of "status" to other males and as an advertisement of mate quality to females. Other primates often use their penises in display; I recalled a picture of a colobus in a primate behavior textbook that I own "threatening the photographer" with an erection. I'd also read that bonobos practiced "sword fighting" while hanging from the trees by their toes.
As evolving human males lost hair and their canines shrank, they lost the primary signaling devices that other primates have. So something else needed to take their place. What better than the penis? In an upright, non-hairy hominid, it stood out quite nicely. In addition, the exposed glans of an erect penis added a bit of color to the display, which any mandrill could appreciate. A patch of pubic hair also helped draw attention to the display.
So there we go. Want to threaten the other males with how big and virile you are? Shake that at them. Want to impress the females with your health and quality? You've got a nice visual signal ready for display.
So that explained a lot-especially the still-existing fascination among both sexes for large penises (codpieces, anyone?), and the fact that so many males feel inadequate if they think theirs is not up to spec.
Female orgasm was trickier. None of the theories I could think of for its evolution could explain its spotty distribution. So perhaps it hadn't evolved at all.
No, I'm not turning creationist. But it struck me that female orgasm could be just a lucky accident of development. Both the male and the female genital organs develop from the genital tubercle. If you're male, some of that sensitive, blood and nerve-filled tissue becomes the glans penis. If you're female, it becomes the clitoris. The tissue is ideally situated to become the glans. There is strong evolutionary pressure for the development of sensitive tissue in the male, because male orgasm is necessary to reproduce. Making it pleasurable makes it even more likely that the male will ensure that his genes are propagated.
So, as a female, you still have that sensitive tissue. But, because it evolved to become the tip of the male penis, it's located some ways away from the vagina. It's not ideally situated for stimulation through intercourse. There hasn't been active selection for women who orgasm easily because, alas, it's not necessary for female fertilization.
So, female orgasm could be just a lucky accident of development; an embryological leftover.
Next installment- what the research showed. As it turns out, I wasn't the only one to come up with these ideas.