MENTAL SEX DIFFERENCES

If maleness and femaleness can involve the body as a whole—its size, plumage, horns, behavior, etc.—then what about the mind? To be female, must you have a female brain? To be male, must you have a male brain? And what would that mean, anyway?

Many neuroscientists who study sex and gender—for example Donald Pfaff, author of Man and Woman: An Inside Story—say that areas of the brain involved in reproduction take two different forms due to the different hormones produced by testes and ovaries during fetal development. Pfaff writes that the preoptic area and medial basal hypothalamus each take two forms. "Destroying the preoptic area greatly reduces male sex behavior almost to zero. Destroying the medial basal hypothalamus greatly reduces female sex behavior, almost to zero.” Pfaff says this is the case in "a wide variety of vertebrate species,” though what the behavior amounts to is species-specific. A great deal of research on brain sex focuses on the mounting behavior of male mice and rats and lordosis in female mice and rats—the way females arch their backs and raise their bottoms to accommodate a male. When it comes to humans, neuroscientists seem to have a better grip on male sex behavior than female; Pfaff says abnormalities in the preoptic area reduce the capacity for erection, penetration, and ejaculation. On the other hand, he admits that the effect of brain and hormonal patterns "in higher primates has been diluted by cultural and social effects.”

In addition to those very limited sex-correlated differences, are there further differences between male and female brains, so that the male brain and the female brain are thoroughly different? Now we must restrict ourselves to one species, as there is no reason to assume the answer is always the same. It seems (but only seems) as if, in humans, the brain/mind is extensively sexed. After all, there are many aspects of the brain with respect to which males as a group differ on average from females as a group. According to psychologist Daphna Joel, "There are sex differences in the size of the brain and of specific brain regions, and in composition of neurons, neurotransmitter content, morphology of dendrites, number of receptors, etc.”

Along the same lines, psychologist Janet Hyde has gathered and exhaustively analyzed hundreds of scientific reports on psychological sex differences, and found some consistent results. For example, in her meta-analysis, girls smile and self-disclose more than boys in 418 and 205 reports, respectively. Boys are more physically aggressive than girls in 111 reports. Consistent with Joel and Hyde, neuroscientist Melissa Hines notes that male and female toy choices are different: boys choose vehicles and weapons more often and girls choose dolls, dress-up toys, and household items more often. If you think this is simply cultural, consider that the same is true of male and female monkeys!

So why not simply embrace the idea that boys have thoroughly male brains and girls have thoroughly female brains? In fact, the data doesn’t support that conclusion. First of all, many of these differences are on the group level only—as Joel, Hyde, and Hines all emphasize. Hyde’s meta-analysis shows that the differences that exist are in the small range in 48 percent of published reports, and near zero in 30 percent. She writes that “within-gender variability is typically much larger than between-gender variability.” Lise Eliot, author of Pink Brain, Blue Brain, says that out of 124 traits that are skewed by sex, 96 are only a little skewed, with over 76 percent of boys and girls being indistinguishable on that trait. Even the traits that are most skewed by sex are still not totally skewed. Males and females overlap in aggressiveness much more than they overlap in height. According to Donald Pfaff, "only the biologically- based more primitive behaviors related to reproduction are really convincingly sexually differentiated in humans.” That is to say, beyond areas relating to reproduction, brains don’t have parts that take two forms, with all males having one and all females having the other.

Furthermore, the traits don’t all line up. If a boy is male-typical in one respect, he can easily be female-typical in another. An aggressive boy might be highly verbal, or a doll-loving girl might be very good at mental rotations. According to Daphna Joel, a picture of an individual’s psychology, in gendered terms, would involve a mosaic. Some of the tiles are gender-neutral shades of yellow or green, and then there are the pink and blue tiles, with varying hues of pink and blue. Biological males don’t have minds built out of all blue tiles, and biological females don’t have minds built out of all pink tiles. The typical boy is a leaning-blue mixture, and the typical girl is a leaning-pink mixture.

So to count as female, do you need female gametes and the right body parts to use them reproductively, and a pink-dominated brain? Likewise, must a male have a blue-dominated brain? It makes sense to define biological maleness and femaleness in terms of gametes plus the bodily features that equip you to use them reproductively. And some of the machinery needed for reproduction is in the brain. However, not every weakly sex-linked mind/brain attribute is essential to being biologically male or female, because you really don’t need them to use your gametes reproductively. The normal man who smiles a lot (pink!) can father children perfectly well, as can the normal woman who’s physically aggressive (blue!). These are simply men and women, not semimen or semiwomen.

 
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