By Lise Eliot, Ph.D.
Several colleagues and I just published a paper in Science, titled "The Pseudoscience of Single-Sex Education." (A podcast by our first author, Diane Halpern, is available here.) It's a provocative title, but we back it up with evidence from three lines of research: educational, neuroscience, and developmental psychology.
Gender segregation in schools is not supported by the voluminous existing research that compares single-sex to coeducational academic outcomes. It is also contraindicated by research in social and developmental psychology, which demonstrates that teachers and students both increase in sexist attitudes and stereotypical thinking when gender is made salient by segregation. My contribution to the article was to evaluate the brain research alleged to support single-sex education. I cover this in a much longer paper "Single-sex education and the brain" that was published in the journal Sex Roles in August.
I got into this debate after writing a book on gender development, Pink Brain, Blue Brain. In researching the book, I originally set out to link sex differences in the brain to the well-known sex differences in children's behavior. But I became increasingly frustrated by the lack of good evidence for brain sex differences in children. I hypothesized that, just as behavior and physical appearance grow increasingly sexually differentiated during development, the brain follows course.
Research on mental rotation, for example, finds no sex difference in boys' and girls' neural processing, whereas several studies have found differences in adults (though the several studies don't yet agree about precisely WHERE in the brain such sex differences lie). Given everything we know about the neural basis of learning (e.g., synaptic plasticity, circuit-level changes, and both gray and white matter volume changes), it stands to reason that as boys' and girls' differential experience adds up, their abilities and brains both grow increasingly disparate.
Men's and women's brains do differ in overall size and gray:white matter ratio. Other data are starting to hold together to indicate that adult males have a somewhat larger amygdala than females and women have greater volume in the ventromedial frontal cortex. None of these differences are large, and it is unknown the degree to which genes, hormones, and experience contribute to them, but it does look like adult men's and women's brains differ more than boys' and girls' brains do.
This is not, however, the message that single-sex school advocate (and Psychology Today blogger), Leonard Sax, has been conveying. In December 2010, he blogged about a PNAS paper by Raznahan et al. which he alleged shows that "sex differences diminish as a function of age" (his emphasis).
To Leonard Sax, this idea is very important. If boys' and girls' brains differ from each other more than adult men's and women's brains differ, it justifies sending boys and girls to different classrooms and teaching them in different ways. Adult men and women may work and govern together, given our highly similar brains, but children aren't ready for this integration, because of their metaphorically pink or blue neural circuits.
As evidence, Sax refers readers to an online movie which is based on Figure 1 of the PNAS paper, but he misinterprets the figure legend. (The movie didn't play for me, and Sax warns readers they may have trouble playing it, but I'm assuming it is the same movie shown in a Wall St. Journal article that repeats Sax's mistaken interpretation, including its faulty caption.)
The figure/movie shows beautiful colorized brains, with cortical areas that are thicker in males shown in a blue-purple color scale, while areas that are thicker in females are shown in white (with no color scale, to avoid confusion with the male-larger color scale). What you see as the images progress from 9 to 22 years of age is that blue/purple areas give way to white areas in the frontal lobe. In other words, during early adolescence, males' gray matter is thicker through much of the cortex, but in adulthood, females' frontal gray matter is thicker, while males' gray matter remains thicker in other cortical lobes.
But Sax misread the figure legend! He states that the white coloring shows areas of no sex difference in cortical thickness, when in fact, the white depicts areas that are thicker in females. So despite what Sax wrote in his Psychology Today blog, the paper by Raznahan et al. does not demonstrate that sex differences are globally greater in childhood and diminish in adults.
Instead, the authors conclude that sex differences "became diminished or inverted in some cortical subregions, but accentuated in others." Leonard Sax just picked the cherry he liked, then threw it to the Wall St. Journal. Jay Giedd, the senior author on the paper, was also quoted in the WSJ piece, but is careful to emphasize that their study cannot be generalized to educational issues.
Interestingly, Raznahan et al. include a sentence in their abstract that Leonard Sax carefully avoids: "Structural change is faster in the sex that tends to perform less well within the domain in question." In spite of his passion for this study, Sax never mentions this statement (admittedly somewhat questionable in its assumptions about functional circuitry. That's because this conclusion directly contradicts Sax's own oft-repeated claim that "while the areas of the brain involved in language and fine motor skills mature about six years earlier in girls than in boys, the areas of the brain involved in targeting and spatial memory mature about four years earlier in boys than in girls."
But I suppose all of this is moot now that Leonard Sax has disavowed neuroscience as a basis for sex-segregated education. His change of heart, new since our articles in Sex Roles and Science publicly debunked him, is encouraging. Is it possible that Dr. Sax now appreciates how exaggerated claims about male-female brain differences reinforce stereotypical thinking among parents, teachers, and students themselves?
