by Angela Saini
Others have pointed out that the Gurs were never clear about the true magnitude of the statistical effect and how significant it actually is. “What proportion of all connections are different is a question they didn’t really address,” says Paul Matthews. Some have even accused the Gurs and their colleagues of cherry-picking the handful of possible pathways, among many, that happen to show some sex difference and using those selectively in their blue and orange illustrations of the brain. This also assumes that all the chosen pathways are being actively used, says Rippon, which isn’t necessarily the case.
“It assumes there is this dichotomy between males and females, that we’re completely separate,” she adds. This is sometimes described as our brains being “sexually dimorphic,” meaning that they take two completely different forms in the same species—in the same way as a penis and vagina are dimorphic body parts. Judging by the final, dazzling pictures, the differences looked huge. Neuroscientist and Tel Aviv University professor Daphna Joel echoed this complaint in a letter to the Proceedings of the National Academy of Sciences, which published the Gurs’ original paper on white matter. “No wonder the main message the reader is left with is of a ‘male brain’ and a ‘female brain’ that seem to have been taken from subjects from different galaxies, not just from different planets,” she wrote.
Certainly, more recent studies suggest that sex differences in parts of the brain are not as big as scientists once thought. A 2016 paper in the journal NeuroImage established that the hippocampus—a brain region that many researchers have claimed is bigger in females—is in fact the same size in both sexes. Led by Lise Eliot, an associate professor of neuroscience at Rosalind Franklin University of Medicine and Science in Chicago, researchers analyzed findings from seventy-six published papers, which together studied six thousand healthy people. Their findings helped dispel the assumption, on physical grounds at least, that women must have a stronger verbal memory, have better social skills, and are emotionally more expressive.
Eliot added that this analysis has shown that there’s also no difference in the size of the corpus callosum—the very region of white matter that Ruben Gur claims is on average bigger in women.
“Sex differences in the brain are irresistible to those looking to explain stereotypic differences between men and women,” she told reporters when her paper came out. “They often make a big splash, in spite of being based on small samples. But as we explore multiple data sets and are able to coalesce very large samples of males and females, we find these differences often disappear or are trivial.”
“Science doesn’t operate in a political vacuum.”
“The criticisms are nonsense, the criticisms are nonsense,” argues Larry Cahill, a professor of neurobiology and behavior at the University of California, Irvine. He tells me that attacks on Ruben Gur’s work by Gina Rippon, Daphna Joel, and others are “spurious” and “bogus.” Sex differences in the brain “range from small to medium to the enormous,” he continues. And on the enormous end of the spectrum are the differences in white matter. He doesn’t accept that scaling up for brain size alone can account for the variations.
For the last fifteen years, Cahill has been on what he describes to me as a “crusade” to prove that the brains of women aren’t the same as the brains of men. “The way I like to put it, it’s not an issue I was looking for. It was an issue that found me,” he explains. “I was a neuroscientist like any other, happily operating under the assumption that it doesn’t make a damn bit of difference whether or not I’m talking about a male or female, outside the very limited brain regions associated with reproduction.” Then, in 1999, he discovered a sex difference in the amygdala, an almond-shaped corner of the brain associated with emotional memory. “I published that in the year 2000, and that was a crossing-the-Rubicon moment,” he tells me.
When he started the crusade, he was warned by senior colleagues not to wade into what was then seen as politically sensitive territory. But he pressed ahead, nonetheless. “I came out of the womb stubborn, and when I’m convinced that I’m right about something, I tend to say ‘Damn the torpedoes! Full speed ahead!’ And that’s what I did. I’m glad that I did.” Studying the literature, he claimed to find “several hundred” papers supporting the idea that there were unexplained sex differences in the human brain. “It’s not the case that sex differences only matter for some tiny structures deep in the brain directly related to reproduction. No. Sex differences are everywhere.”
He adds that scientists like Ruben Gur are fully entitled to speculate about what their data might tell us about human behavior. “They engage in perfectly reasonable speculation about what these differences might mean. Just as you and I might engage in perfectly reasonable speculation about what the anatomical differences may mean.”
For Gina Rippon, this has become a tiresome battle. “There are people like Larry Cahill who call us ‘sex difference deniers,’ but it’s the same kind of attack that gets put on feminism at each stage, or whatever wave you think you’re in,” she tells me. “I’m not paranoid or a conspiracy theorist, but there is a very strong, quite powerful backlash in this area. It’s kind of acceptable in an odd way, which is not true if you’re talking about race or religion.” As someone outspoken about sexism in science, she occasionally receives misogynistic e-mails from men who disagree with her. The worst ones attach photos of their genitalia.
Another recent clash was with the British chess grandmaster Nigel Short. In 2015 he wrote a provocative article in a chess magazine trying to explain why there are so few female players. “Men and women’s brains are hardwired very differently, so why should they function in the same way?” he asked. “I don’t have the slightest problem in acknowledging that my wife possesses a much higher degree of emotional intelligence than I do. Likewise, she doesn’t feel embarrassed in asking me to manoeuvre the car out of our narrow garage. One is not better than the other, we just have different skills.” When his comments went viral, Rippon was invited to talk about them on the national BBC radio show Woman’s Hour. “He thinks that there aren’t very many women chess players because they can’t play chess. It’s actually that they don’t play chess,” she argued. Female chess players have said that the aggressive, macho, and sexist atmosphere of professional chess can drive them away.
Rippon tells me that in her field it’s impossible not to see the scientific data politicized, especially when it enters the public realm. “Science doesn’t operate in a political vacuum,” she explains. “I think there are some sciences which can be more objective than others. But we are dealing with people, we’re not the Large Hadron Collider.” Unlike particle physics, neuroscience is about humans, and it has profound repercussions for how people see themselves.
“It’s not something that people don’t know much about. This is about everybody’s lives. Everybody has a brain, everybody has a gender of some kind,. . .they’ve either been in a mixed-sex school or they have worked in a mixed-sex environment. They’ve got boys and girls. So they see differences. And so, when you say there aren’t really any, they say you’re wrong,” she adds. She has seen it for herself when giving lectures about her work. “I go into schools and talk to girls, and their whole expectation is far more gendered than it used to be. These are toxic stereotypes and these girls’ futures are being affected by this.”
According to social psychologist Cliodhna O’Connor based at Maynooth University in Ireland, Ruben and Raquel Gur’s study on white matter is a textbook example of how research into sex differences can quickly become absorbed into people’s wider gender stereotypes. When the paper was published in 2014, she decided to monitor reaction to it. What she found was shocking. “It was covered in all the major national newspapers,” she tells me. “The main meaning that was taken out of it was just the fact that men and women are fundamentally different in some very essential, primitive, unavoidable way.”
O’Connor found that people in the thousands commented online and discussed
the research on social media such as Twitter and Facebook. “As a conversation evolved, cultural and gender stereotypes were progressively projected onto that scientific information, to the extent that people were describing the research as the discovery of stuff that wasn’t even mentioned in the original scientific article,” she says. People latched on to the idea in the press release, but not in the paper, that women are better at multitasking. Before long, they were using the study to argue that men are more logical while women are more emotional. “That dichotomy wasn’t mentioned either in the press release or the original article, but it was kind of spontaneously introduced when people were discussing the research,” she adds.
O’Connor tells me that this kind of distorted reaction to brain studies on sex and gender is common. “No matter how neutral the initial presentation of information, people do tend to gradually recruit the stereotypes and the associations that are prevalent in a culture and then project that,” she explains. It’s part of being human. We tend to interpret new information by categorizing it, using whatever understanding we already have, even if this is prejudiced.
Another factor that prompts people to behave this way is that we like to justify the social system we’re in. If everyone around us thinks that women are less rational or worse at parking, even the thinnest piece of information that reinforces that assumption will be pasted into our minds. Research that confirms what appears to be obvious seems right. Anything that contradicts it, meanwhile, is dismissed as aberrant. This is why, when theories come along that challenge gender stereotypes, we may also find them more difficult to accept.
But all this still leaves one unanswered question: If the brains of women and men aren’t so different, then why do researchers like Ruben Gur and Larry Cahill keep seeing sex differences?
“If you take any two brains, they are different.”
At the turn of this century, Londoners were surprised by a revelation about one of their most recognizable groups of workers. The brains of the city’s black-cab drivers, who are famous for their perfect navigational ability, down to the smallest and most hidden side streets, were being physically altered by their work.
Neuroscientist Eleanor Maguire at University College London discovered that the mental feat of memorizing the layout of twenty-five thousand streets and thousands of landmarks, known as “The Knowledge,” could be changing the size of a cabbie’s hippocampus, a region associated with memory. This piece of research had enormous implications. It helped confirm an idea that scientists had already been developing since the 1970s, particularly through animal studies: that the brain isn’t set in stone in childhood but is in fact moldable throughout life.
“These changes are terribly tiny, but they are measurable,” says Paul Matthews. Studying musicians, basketball players, ballet dancers, jugglers, and mathematicians has confirmed that brain plasticity is real. In the context of sex difference research, it also raises an important question: If intense experience and learning a new task can shape a person’s brain, could the experience of being a woman shape it as well? Could plasticity therefore explain the sex differences that are sometimes seen in the brain?
According to Gina Rippon, psychologist Cordelia Fine, and gender scholars Rebecca Jordan-Young in New York and Anelis Kaiser in Bern, Switzerland, plasticity is a phenomena that has been oddly ignored when people talk about sex differences in neuroscience. “Our brain actually absorbs a lot of information all the time, and that includes people’s attitudes to you, expectations of you,” says Rippon. Her own work is driving her toward the view that it isn’t just supreme feats of learning or traumatic experiences that affect the brain but more subtle and prolonged things, too, like the way girls and women are treated by society.
This idea has in turn been woven into an even bigger and more radical new theory that might explain how the small sex differences we occasionally see in brain composition might emerge. Rippon, Fine, Jordan-Young, and Kaiser have argued that biology and society are “entangled”—that they work in concert with each other, through mechanisms like plasticity, to create the complicated picture we call “gender.”
Their ideas are supported by a growing body of evidence on how gender differences shift over time. Research in the 1970s and 1980s revealed that the number of American boys with exceptional mathematical talent outnumbered girls by thirteen to one. At the time, it was seen as a shocking imbalance. Since then, however, as psychologists David Miller and Diane Halpern (Halpern is a former president of the American Psychological Association) have pointed out, this ratio has plummeted to as low as four, or even two, to one. In a paper published in 2014 in Trends in Cognitive Sciences, they note that there have been equivalent drops in gaps in general performance on math tests in the United States.
But how? If mathematics ability were rooted in biology and sex differences were fixed, then we wouldn’t expect to see these changes over time. What’s more, we would expect the differences to be the same everywhere. And they’re not. Among Latino children in American kindergartens, for example, girls tend to be the best achievers in mathematics tests, not boys. “Challenging the notion of universal male advantage in mathematics, sex differences in average mathematics test performance are not found in many nations and are even reversed (female advantage) in a few,” Miller and Halpern observe. What looks like a biological difference in one particular place and time can turn out to be a cultural difference after all.
Plasticity and entanglement suggest that, like London cabbies memorizing street layouts, culture can have a ripple effect on biology. We know, for instance, that playing with certain toys can actively affect a child’s biological development. “We’re good at what the brain allows us to be good at and, as we become good at something, our brain changes to enable that,” explains Paul Matthews. Playing action video games or with construction sets, for instance, improves spatial skills. So if a young boy happens to be given a building set rather than a doll to play with, the stereotype of males having better spatial skills is physically borne out. Society actually ends up producing a biological change.
On the flip side, exposing someone to bad stereotypes can impair their performance. In one controversial study that Miller and Halpern cite, women who are reminded of negative stereotypes about female abilities in math go on to perform worse on math tests. “Removing stereotype threat can improve both men’s and women’s academic achievement,” they write.
With all these effects on the brain, in a world as gendered as ours, says Rippon, it’s actually surprising that we don’t see more sex differences in the brain than we do. But then, so many factors other than our gender affect us. Plasticity and entanglement imply that every single brain must be unique, for the simple fact that every person’s life experience is different. It is this, argues Daphna Joel at Tel Aviv University, that makes looking for differences between groups so fraught with error. Evidence of sex difference in the brain is statistically problematic because each brain varies from the next.
This may go some way to explaining why neuroscience and psychological studies often get different results when they’re looking at the same thing. If one piece of research doesn’t confirm a sex difference where another claims to have found one, scientists sometimes assume that they must have made some mistake and pulled out a false negative. “They have many explanations to explain why they fail to find differences,” says Joel. “They never say that maybe there are no differences, and the fact that someone else found a difference is just a chance finding, and it’s actually a false positive. It’s especially amazing, because in science this is the first thing you need to think, that if you don’t find difference, maybe the theory is wrong.”
This way of thinking suggests that it’s not varying environments, false negatives, or bad experiments that are obscuring evidence of the brains of women and men being sexually dimorphic. It’s that there isn’t dimorphism in the brain to begin with. “Every brain is different from every other brain,” Gina Rippon explains. “
We should take more of a fingerprint type of approach. So there is some kind of individual characteristic of the brain, which is true of the life experiences of that person. That’s going to be much more interesting than to try to put them all together, trying to squeeze into some kind of category.”
Daphna Joel’s theory, published online by the Proceedings of the National Academy of Sciences at the end of 2015, states that, rather than being distinctly male or female, the brain is a unique “mosaic” of characteristics. In any given person, you’re likely to find features in a form that’s more prevalent in men and also in a form that’s more prevalent in women. To illustrate, she gives me the example of porn and soap operas. Watching porn is an interest strongly associated with men, but not all men watch porn, and of those who do, some also love watching soap operas, which is an interest commonly associated with women. Add up all the different interests that overlap and, in any person, you’re left with a huge gender mix. “Of course, most of the features will just be in an intermediate form, something that is common in both males and females,” she adds.
The idea of exploring a range of features across the brain as a whole came as a revelation to Joel. It was sparked by studies reporting that environmental factors can reverse the effects of some sex differences in rats. “Regardless of how stressed your mother was when she was caring for you, where you live, or what you eat, your genitals will not change. The sex effects on the genitals are fixed, always the same. But when I saw that the sex effects on the brain can actually be opposite, so what you see in one sex under some conditions, you can see in the other sex under other conditions, I realized that I was using sex effects on the genitals as an implicit model when thinking about sex effects on the brain,” she tells me. “This is not a good model.”