Male and Female Brains

My trek through the literature on sex differences continues. These podcasts from NeuroGenderings III are interesting, especially the talks by Anne Fausto-Sterling and Rebecca Jordan-Young.  The Jordan-Young talk led me to version 2, which she gave at a symposium in honor of Fausto-Sterling (video here).  And from there, I was led to two papers--"Male or Female? Brains are Intersex," by Daphna Joel; and "Reframing Sexual Differentiation of the Brain," by Margaret McCarthy and Arthur Arnold (which I haven't read yet).  A nice break in the technical slog: there's also this TED talk by Daphna Joel.

The Joel paper and talk (parts of which are highlighted by Jordan-Young) makes me wonder about several things.   First, a philosophical question.  What would you need to find out about brains to say there is a male brain and a female brain?  Joel is emphatic that there is no such thing as a male brain or a female brain because there aren't two forms for brains, just differences in averages on hundreds of parameters.  Plus, a person can score "female" on one parameter but "male" on another--the scores don't line up consistently. Plus, the scores on various parameters can change over time, for one individual, due to environmental factors like stress.  But what about the reproductive machinery in the brain, which takes different forms in males and females?  Donald Pfaff writes, "The most striking sex difference is that the female hypothalamus can command the pituitary to put out pulses of hormones that will cause ovulation by the ovary, whereas the male hypothalamus cannot do that."  (Man and Woman: An Inside Story kindle loc. 586).   How is it that this difference in the hypothalmus doesn't mean that there actually is a male brain and a female brain?  I have to surmise that "male brain" means, to Joel, a brain that's male through and through.  A difference in one part won't do.  Likewise for "female brain."

But why?  There are male and female bodies, right?  And they're male and female because of differences in certain parts. Among other things, males and females have different gonads.  You wouldn't say "there are no male and female bodies" just because male and female kidneys, livers, hearts, gall bladders, and so on, don't take different forms.  So I am honestly puzzled by this insistence that there are no male and female brains.

I suppose what's going on here is that folks like Joel want to disabuse people of a popular error--the belief that the brains of men and women are different through and through.  That is not the case (if Joel is right), though certain parts are different (if Pfaff is right).  I would think that, using language carefully and literally, the difference at the level of parts means there are male and female brains.  It's just that this isn't the super big deal some people say it is--like The Female Brain author Louann Brizendine.

Now for an empirical question. Jordan-Young embraces the part of Joel's paper that says it's impossible to say how one individual will score on one sex-dependent parameter, based on how they score on another. The various parameters don't necessarily line up, making each individual's mind/brain a pink, blue (and other) mosaic.  What I wonder, though, is what kinds of covariance you find between the different parameters.  Given a person scoring high on aggression, is there a higher probability that they will score high on other "male" traits like willingness to take risks?  If a person scores high on compassion, is it more probably they will score high on sensitivity and squeamishness?  This is really an important question for understanding sex, particularly if you want to evaluate a point Jordan-Young makes many times: sex is not a mechanism.  If there's even just pretty good covariance, it makes you think sex probably is a mechanism.  Something's got to be making these traits tend to cluster together (if they do).

The covariance question is an important question for me because I'm trying to think about the way parents react to the sex of their children, on ultrasound or at birth. If the mosaic of traits for each individual shows no internal coherence--from one tile you can't predict the others at all--then we ought not think much of it when we hear "it's a boy!" or "it's a girl!".  But if there's quite a bit of internal coherence--from one tile you can predict the others pretty well--then the natal sex of your child tells you more.

Questions, questions.  In another life I will study the neuroscience of gender full time, because it's a vast subject and awfully interesting.