Sex On The Brain

Sex On The Brain – the biological differences between men and women, Deborah Blum, Viking, ISBN 0-670-86888-4.

There is seemingly no end to the making of books about the differences between men and women. They vary immensely both by approach taken, by the degree of bias, and by quality. There are a lot of bad books out there and a few good ones. This is one of the good ones – one of the very good ones.

Deborah Blum is a science writer with impressive credentials, among them the Pulitzer prize she won for Monkey Wars. Her writing is clear, literate, and witty. The dust jacket has enthusiatic (and warranted) praise from E.O. Wilson, Matt Ridley, Frans de Waal, and Helen Fisher.

The history of the “scientific” investigation of human sex and the differences between the sexes has been a sorry one. There has been a running thread of drawing broad conclusions from thimblefuls of data, conclusions that reflected the biases and predilictions of the investigator rather than legitimate reasoning.

The reason is obvious. Sex, differences between the sexes, and gender roles are very important to us. They are interwoven into our culture, our personalities, our religions, our art, and our politics. Having theories about gender, theories that tell us who we are and why we are the way we are, is necessary. The science, however, is hard. Human biology is monumentally complex; human cultures are complex; they interact in complex and poorly understood ways. It is fair to say that we are only recently getting a good handle on how little we know.

So what do we know and how do we know it? What has science learned of late? Quite a bit of work is being done. Sensationalized versions of what the scientists are learning appear regularly in the media. What you see in the TV specials, the pop news magazines, and the newspapers is often a long ways from what the scientists really have discovered.

Modern investigations into sex and the differences between the sexes involve a wide variety of disciplines such as evolutionary biology, neurophysiology, molecular biochemistry, genetics, anthropology, and developmental psychology. Blum does a pretty good job of covering the ground, giving us her best shot at honest unbiased reporting. What it seems to come down to is that there are differences between the sexes, differences that are not just differences of plumbing and gender socialization. The trouble is that mostly we don’t know what these biological differences mean. Here are a few bits and pieces drawn at random.

Sweaty t-shirts

Female mice and female humans are attracted to males whose MHC (major histocompatibility complex) genes are least like her own. These genes code for the disease detectors in the immune system – detectors, not killers. The more variety (within the species limits), the better. One of the experiments that bore this out was the famous sweaty T-shirt experiment.

A group of college men and women were tested. Each man was given a clean cotton T-shirt and asked to sleep in it over a weekend, avoiding things such as spicy foods, cologne, deodorants, smoking, drinking, and sex, the objective being to get the T-shirts smelling of uncontaminated male sweat.

Each woman was seated alone in a room at the time of her ovulation (the sense of smell is more acute then) and sniff each one. “The women were asked to rate every shirt for sexiness, pleasantness, and, I suppose, basic reek, although the scientists called it intensity of smell.” And it turned out that the sexiness of the shirts correlated with the degree of difference in the MHC genes.

Low testosterone hubbies

Tetosterone (and the other androgens) has three roles. One is to promote the development of male plumbing during development. One is to facilitate muscle development, etc. The third is to facilitate competitive aggression responses. Male testosterone levels bounce around all over the place. See a woman; the level jumps. Win a competition; mucho testosterone. Lose it; the level sags.

In polygamous species the dominant males are hyped on testosterone. In highly monomagous species males and females are very much alike in morphology and their testosterone levels are nearly identical. Homer sap is somewhere inbetween. Evolutionarily speaking we’re not a monogamous species but we’ve been evolving in that direction.

Which brings us to hubbies. Men who are in good, happy marriages tend to have lower basal levels of testosterone. The effect is quite marked.

Being pregnant is bad for your health

No, I’m not speaking of the obvious problems. The most prominent of estrogens is a hormone called estradiol. One of the major functions of estradiol is the enhancement of the immune system. The biological advantages that women have, health wise, are due to in large part to their superior levels of estradiol until menopause. (Estradiol production shuts down after menopause.) However the catch is that estradiol production also shuts down during pregnancy, apparently to keep the immune system from rejecting the fetus.

Of course, being male and pregnant is much worse for your health.

Homosexual sheep

It begins to look like it’s not really appropriate to lump male and female homosexuals together – male homosexuality is a variant of male sexuality and female homosexuality is a variant of female sexuality. But about those sheep.

Instances of male homosexual behaviour in other species is quite common. In most species it is a transient thing rather than a persistent preference. It may be a testosterone overload, part of a dominance ritual, or even just confusion on the part of an inexperienced young male. Given the chance they happily mate with females. Not so with sheep.

There are a significant percentage of rams that simply want to mate with other rams and have no interest in mating with ewes. Can’t get them to do it with ewes. They just don’t want to. Why, nobody knows. It’s hard to believe that they have dominating mothers.