This article first appeared in Issue 14 of our free digital magazine CURIOUS.
The question of whether there’s a tangible difference between male and female brains is one of the most compelling – and controversial – in the history of neuroscience. On reading the title of this article, you might have immediately rolled your eyes: “What’s she going on about? Surely, we left these kinds of conversations behind with the suffragettes!” Or, you might have nodded sagely: “Of course there are differences, and I can’t wait to read an informed treatise on the subject whilst my wife fixes dinner.” As it turns out, we’re going to have to disappoint both hypothetical readers to some degree.
There are some differences, just as there is a difference in average height between biological males and females. The question of just how profound these differences are is a trickier one to answer, as is the arguably more important one: does it even matter?
The historical perspective
The idea that something fundamental sets male and female brains apart really gained momentum in the 19th century. As explained by cognitive neuroscientist Gina Rippon in her book The Gendered Brain, this era saw an increasing push from women for greater rights and inclusion in society. For some reason, this disturbed the men who had enjoyed a monopoly on all the power and influence, and galvanized the scientific community into producing evidence that women were far too incapable and fragile to be taken seriously.
Enter the “science” of craniology. The idea was simple: a bigger brain meant greater intelligence. Through much fudging of data and a somewhat laissez-faire approach to experimental consistency, many “measurements” that seemed to prove that men had the better brains were produced.
However, the theory did not stand up to closer scrutiny. Rippon explains how a team of mathematicians – including statistician Alice Lee, one of the first women to graduate from the University of London – produced data that led to the swift abandonment of craniology after demonstrating that some of the smallest heads in their sample belonged to a group of celebrated, and male, anatomists. As they say, size matters.
This wasn’t the only – or the last – attempt to use scientific thinking to demonstrate the alleged immutable differences between the sexes. For example, there was the argument made by Edward H. Clarke in Sex in Education; or a Fair Chance for Girls, that exposing women to the same teaching methods used to educate men was to risk “neuralgia, uterine disease, hysteria, and other derangements of the nervous system,” including such choice insights as, “Boys must study and work in a boy’s way, and girls in a girl’s way.”
You might be surprised (or horrified) to hear similar ideas persisted in education well into the 21st century. As neuroscientist Lise Eliot explained for The Conversation in 2021, “About a decade ago, teachers were urged to separate boys and girls for math and English classes based on the sexes’ alleged learning differences,” adding that “Fortunately, many refused.”
Archaic ideas about how males and females think and learn proved hard to shake off, and the advent of more sophisticated scientific techniques did not see the end of this debate.
New questions, but still no answers
In the age of EEGs, PET scans, and MRIs, a huge amount of energy has been devoted to finding an anatomical or functional difference between male and female brains. There’s no shortage of papers claiming evidence for this, but there’s also a lot of work that falls on the opposite side, including a 2021 review led by Eliot that roundly rejected the notion of sexual dimorphism in the human brain.
New ways of studying the brain only meant new ways of trying to find the difference that many remain sure is there, lest it reveal the reason behind supposedly sex-specific behaviors. As Rippon explains, “In looking for sex differences, neurologists cheerily matched their assumptions about which bits of the brain were the most important to their findings about which bits of the brain were largest in males, even if it meant reversing earlier conclusions.”
Let’s get one fact out of the way: males really do have larger brains, on average. The simple reason for this is that males, on average, have larger bodies. Similar differences, some even more pronounced, can be observed in other organs.
One problem, though, is that no one can seem to agree on the best way of correcting for this very real average difference in brain sizes. It’s also much more difficult than your biology textbooks would have you believe to go around linking certain parts of the brain to specific functions. To illustrate this, Rippon details the example of what she calls the “corpus callosum wars” (not the title of the next Star Wars spinoff).
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The corpus callosum is a bundle of nerve fibers, part of the brain’s white matter, which connects the two hemispheres together. A paper back in 1982 found that in females, part of the corpus callosum was larger. The fact that this difference was so minor as to be statistically insignificant did not seem to matter, and the idea took root.
It seemed to offer a neat explanation for some of the “known” differences in how men and women think. A smaller corpus callosum equals fewer connections between the left and right hemispheres. This should allow the two hemispheres to perform their supposed separate functions more effectively, giving men an advantage in the fields of mathematics and science, while women were hindered by the constant interplay between the emotional and rational halves of their minds. We’ll pause there while you stop laughing.
The fact that this finding, and others like it, gained so much traction speaks to another facet of this conversation: publication bias. Given how ingrained ideas about the “proper” places for males and females are in many societies, it’s perhaps unsurprising that research supporting these ideas is so attention-grabbing.
The role of environment
Modern neuroscience is learning more every day about just how adaptable the human brain is. Our brains physically change when we acquire new skills.
The classic example is that of London taxi drivers, who undergo a training program called the Knowledge to memorize the meandering layout of the city streets. Learning the Knowledge has been demonstrated to change the brain structures of those drivers who pass, most notably by increasing the gray matter in the posterior hippocampus, which is linked with spatial memory.
Other skills, like learning a musical instrument, also leave their mark on the brain. What this suggests is that differences between two individual brains may have more to do with their different experiences, rather than their biological sex.
The way young male and female children are treated in society could also be affecting their brain development. Much attention has been paid to the important question of gender biases in toys, and whether societal pressures are restricting girls’ future career choices.
Although some research has found that preferences for stereotypically “male” or “female” toys exist even in monkeys – who presumably have not had to endure a barrage of pink or blue advertising from birth – it would be difficult to say for certain that differences between male and female brains are innate when most people still grow up in an environment where a child’s gender expression affects something as basic as how adults speak to them.
When things go wrong
One sticking point in this debate has been the fact that certain psychological, neurological, and developmental disorders affect one sex more than the other. How else can that be explained other than some fundamental difference in their brains?
A 2020 study in PNAS found some differences in the sizes of brain areas between males and females, as well as different patterns of gene expression that were linked to sex chromosomes – something that had previously only been shown in mice. The authors suggested that learning more about sex-specific gene expression patterns could reveal more about sex differences in brain disease.
However, we also can’t ignore the fact that some of what we thought we knew about the different sexes’ susceptibilities to various conditions is turning out not to be true.
One example of this is autism, once thought to be something that almost exclusively affected males. In fact, under something called the brain organization theory, it was thought that sex hormones present during fetal development permanently “masculinized” boys’ brains in ways that made them, among other things, more likely to have autism. Recently, there’s been a rethink and a huge increase in our understanding of how autism presents differently in women and girls, leading to many more diagnoses.
Where does that leave us?
We can say with certainty that there are some differences between male and female brains, and that there’s more to be discovered about where these arise from. Redressing the balance by including females – be they human or otherwise – in research, where this has not always been a priority, would be a good start.
As to whether these differences tell some secret about the capabilities or aptitudes of men and women, that is becoming less clear with each new addition to the literature.
More interesting and instructive answers might come from looking at our brains as a function of the lives we’ve lived and experiences we’ve had, not only the sex chromosomes we were born with.
And thankfully, in much of the world at least, fewer and fewer of these potentially brain-altering life experiences are now solely the preserve of the menfolk.