Jul 112010

figleaf, over at realadultsex asked some highly pertinent things about the role of male orgasm in the evolution of humans. So much so, that I’m taking two posts to discuss them.

In Part 1 I talked about how we might investigate the idea that men’s orgasms function as a reward mechanism for ejaculation. Part 2 – this part – is about what else men’s orgasms might be for.

Figleaf said, among other things:

[...] I just think it’s really, really critical not only to ask what use orgasms serve in women (which is still a darn good question) but to ask what purpose they serve in men.

My guess is that homology really does play a big role — we really do start out with the same genital buds, and as far as I know there’s nothing specific on the Y chromosome that codes for more than testosterone, with all other sex differentiation resulting from testosterone’s affect on the expression of more universal genes.

A few years ago I even speculated (only slightly seriously) that men’s bigger-than-strictly-necessary orgasms might be due to homologous benefits deriving from completely nonsexual selective pressure based on women’s need to grow some kind of / any kind of padding for the urethra in the birth canal. (My big-headed son damaged my partner’s urethra so badly coming out her bladder nearly ruptured before they could get a catheter through it.)

Anyway, my burning questions are a) why should we assume men need big orgasms either, b) how much of a role does homology really play, and c) can we be certain big orgasms are directly selected for in either men or women?

To begin with, here’s the best supported theory about where women’s orgasms came from:

They are the result of biological homology. “Homology” means having the same biological origin. An example: women have orgasms for the same reason men have nipples. They are HUGELY vital (it’s argued) to the survival of the species, so it’s just cheaper, biologically, to put them in place developmentally very very early, and then about half the time an organism becomes female and requires those nipples in order to feed her offspring, and in about a half the organism becomes a male and the nipples do no harm.

If we have orgasms for the same reason, the claim relies on this idea that men’s orgasms are, like nipples, crucial for our survival. Which is a claim not without problems – see part 1.

I’ve never before heard the idea about the homology of women needing urethral padding resulting in men’s orgasm. I suppose it would go something like this:

Women having dangerously narrow birth canals (due to ability to walk upright) but also bearing babies with massively big heads (due to ginormous brains) results in cephalopelvic disproportion, which results is highly dangerous, painful childbirth. So the body evolves the urethral sponge to protect the urethra during childbirth, men get one too (in the form of a prostate) which results in big but not strictly functional orgasms.

Interesting! Honestly I know nothing about the evolutionary origins of the prostate/urethral sponge, so I can’t comment. Mostly when people talk about the biology underlying orgasm they talk about the phallus (penis and clitoris) because that’s where the bulk of the sensation comes from.

My own personal theory – which could be utter bullshit – is that human male orgasm is about attachment. Certainly it’s all the same chemicals involved, the same brain parts, etc – though in all honesty those brain parts are involved in more or less every motivation system. Some evidence suggests that attachment style is associated with orgasm frequency. If I’m right, then orgasm was NOT selected for directly, but indirectly; it was a spandrel, an evolutionary leftover that sexual selection picked up and thought, “Huh, I bet I can do something with that!”

Here’s the general idea:

There’s no question that orgasm IS a reward – how strong and how long lasting, I don’t know. There’s also quite strong evidence that orgasm is linked to attachment. Attachment is there so that infants and adult caregivers bond, but it also bonds adults to adults.

So here we are, this species with MASSIVELY dependent offspring – due to that cephalopelvic disproportion thing, we’re born too early, utterly helpless and dependent for a LONG TIME – and the more adult care we can get the better. If a male partner is attached to a female, maybe he’ll participate in her survival and in her offsprings’ survival. Men provided only a small proportion of the calories in the environment of evolutionary adaptedness, but it COULD (maybe?) be the case that that small proportion made a large difference in survival, and if you’re the attachment object of a man who almost literally brings home the bacon, maybe he’ll favor you with some extra. More fat, more protein, better brain development and less malnutrition, ya know?

So IF – IF – orgasm attached a male to his partner and IF – IF – that attachment results in better nutrition for mother and offspring, then orgasm has resulted, via attachment, in better survival of offspring to reproductive age.

One of the things I like about this theory, for totally unscientific reasons, is that it implies that a “good genes father” and a “good parenting father” can be one and the same, something the standard ev psych party line rejects. THEY tell a story about women looking for healthy genes to get pregnant and nice, rich men to parent the children. There’s interesting evidence around this idea, but it is not contradictory to this orgasm idea; if a man – let’s just say it out loud and get it over with – if a man falls in love with a woman and therefore takes care of her and the baby, his genes get farther. Orgasm, I’m suggesting, is there to make him attach and keep him attached. And it would HAVE to be a big orgasm to counter the ways in which testosterone etc reduces sensitivity to oxytocin.

Call it the sexy daddy hypothesis.

A WHOLE LOT of caution is necessary in all this because the differences between males and females is tangled up with the SIMILARITIES between males and females. Males and females, after all, are essentially all the same parts, just organized differently. Sorting out the ways in which the differences are actually relevant or important is neither simple nor easy.

But that’s my theory. Could be wrong.