As efforts to improve diversity in science, technology, engineering and maths accelerate, so the voices of those who question those efforts seem to get louder.
They say the STEM gender gap has its roots in innate biology, that men are inherently better at or more interested in these subjects. One of their favourite supporting arguments is that differences in male and female brains are clearly influenced by prenatal testosterone. Is there any truth in this claim?
As a biologist, I appreciate that genes and hormones are important in brain and behavioural development. But my research over the past 20 years indicates that the differences between boys’ and girls’ brains are subtle, and that testosterone isn’t a key determinant of interest in or aptitude for STEM subjects.
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First, in spite of decades of MRI studies, there is little evidence that boys’ higher prenatal exposure to testosterone affects their brain structure or function. Most recently, the two largest studies of the brains of newborns found between boys’ and girls’ functional brain networks and that prenatal testosterone exposure had a on specific neural structures.
Even the most clear-cut gender difference in infant behaviour – verbal ability, which develops more slowly in boys – hasn’t been linked to prenatal testosterone.
Of course, male and female brains are different, but not in the way the diversity critics claim. At birth, boys’ brains are 6 per cent larger on average than those of girls, but boys’ birthweight is also typically about 7 per cent heavier. This difference in brain size has long been known to parallel sex differences in height and weight across the lifespan. Every other organ, such as the heart and kidneys, is also some 15 per cent larger in males.
All in proportion
However, there are no specific regions of the brain that are disproportionately larger in one sex or the other, another overstated fallacy of the . Once you account for a person’s overall brain or head size, the difference between men’s and women’s specific brain regions shrinks to “” levels, such that gender accounts for a mere of the total variance in structure sizes across the population.
In a similar vein, my colleagues and I disproved about two structures in the limbic, or emotional brain: the , long rumoured to be larger in women, and the , often said to be larger in men. Using meta-analysis of MRI data from dozens of studies and thousands of participants, we found that both structures are larger in men when measured “raw,” but exhibit no sex difference when their volumes are adjusted for subjects’ overall brain volume.
Even the most about brain-sex differences in recent years – a paper from University of Pennsylvania researchers claiming that women’s brains are more connected between hemispheres – turns out to be an of brain size.
What does help explain the gender gap is neuroplasticity. Whether the task is writing computer code, reciting poetry, solving differential equations or even the simple act of , there is little we humans do that isn’t acquired through . If one gender is a lot better at mentally rotating objects, it is because their brains have had a lot more practice at mentally calculating object movements and trajectories.
So the issue isn’t how testosterone “hardwires” the brain for different interests and skills. Rather, it is how boys and girls spend their time and envision their futures, given brains that start out much more similar than different. And to understand this divergent development, we need look no further than the highly gender-divided culture that children are reared in.
As has been widely noted, women were actually much during its earliest days, before the field developed a “male” label. They will get there again, but first we must move beyond the myth that testosterone sets some kind of limit to women’s achievement in tech or other high-status jobs.
