The clearness and strength of the brain of the woman prove continually the injustice of the clamorous contempt long poured upon what was scornfully called “the female mind.”
—Charlotte Perkins Gilman, Women and Economics, 1898
On the twenty-ninth of September, 1927, a dead brain made the news. It appeared on page five of the Cornell Daily Sun.
Before I tell you why, let me tell you about this brain’s owner. It belonged to the teacher and writer Alice Chenoweth Day, who by the time of her death was better known by the pen name Helen Hamilton Gardener. Since 1875 Gardener had lived with her husband in New York, where she was a passionate advocate for the rights of women. One of her books, Facts and Fictions of Life, railed against the way women were kept subservient by society though unequal education and marriage.
Gardener’s work echoed that of suffragist and writer Eliza Burt Gamble, who was her contemporary. She, too, was incensed by the way scientific “facts” were being used to hold women back in their fight for equality. In 1888 Gardener gave a talk titled “Sex in Brain” at the convention of the International Council of Women in Washington, DC, complaining that scientists studying the brain claimed that women’s brains were lighter than men’s, and that by extension, they must also be less intelligent. One of the most high-profile men to suggest this was William Alexander Hammond, no less than surgeon general in the US Army and one of the founders of the American Neurological Association.
Gardener didn’t have the education she needed to prove that Hammond was wrong. Few people, she lamented, “had the anatomical and anthropological information to risk a fight on a field which assumed to be held by those who based all of their arguments upon scientific facts, collected by microscope and scales and reduced to unanswerable statistics.” If scientists wanted to make such outrageous assertions, what could she or any other layperson do to fight them?
“I finally, with fear and trembling, made up my mind to learn what he knew on this subject or perish in the attempt,” she announced. She ended up working alongside New York doctor Edward Spitzka, soon to become president of the American Neurological Association, in the hope of understanding the brain’s anatomy enough to be able to challenge the great William Hammond. It took her fourteen months to dissect his statistics, while corresponding with twenty anatomists and doctors across New York.
In a beautifully clever and witty letter eventually published in Popular Science Monthly, she revealed that all her experts couldn’t distinguish between a male and female brain at birth. Even among adults, it would be a mere guess whether a given brain was male or female. The overlap between the sexes was just too big. Her sharpest observation was that the weight of a person’s brain couldn’t be a measure of intelligence, anyway. It was the ratio of body weight to brain weight or body size to brain size that was important. If that weren’t the case, she remarked, “an elephant might out-think any of us.” Indeed we should expect a creature as huge as a whale, with its correspondingly huge brain, to be a genius.
Her arguments were compelling, but apparently not compelling enough. William Hammond replied to Gardener with a hefty five-page letter of his own (he complained that he nearly didn’t write it at all because he found the tone of hers was “so bad”). Mocking her “twenty leading brain anatomists,” he repeated his own results. He added, “Ten men who were remarkable for their intellectual development” were found to have particularly heavy brains, on average weighing more than fifty-four ounces. “Now, let Miss Gardener and the ‘twenty leading brain-anatomists,’ etc., search the records of anthropology and their own immense collections for the brain of a woman weighing as much as the least of these,” he challenged.
A month after her letter was published, George John Romanes, an eminent evolutionary biologist and friend of Charles Darwin, also weighed in. “Seeing that the average brain-weight of women is about five ounces less than that of men, on merely anatomical grounds we should be prepared to expect a marked inferiority of intellectual power in the former,” he argued in Popular Science Monthly. “We must look the facts in the face. How long it may take the woman of the future to recover the ground which has been lost in the psychological race by the woman of the past, it is impossible to say; but we may predict with confidence that, even under the most favourable conditions as to culture, and even supposing the mind of man to remain stationary,. . .it must take many centuries for heredity to produce the missing five ounces of the female brain.”
The fight over those missing five ounces was a bitter one, and it was never resolved in Helen Hamilton Gardener’s lifetime. Scientists like William Hammond and George John Romanes “gave a black eye to their facts in preserving a blind eye to their faith,” she warned.
Gardener promised, fittingly, to leave her brain to science before she died. In 1925 it ended up in the Wilder Brain Collection at Cornell University (it’s still there, preserved in a jar). And this is how the Cornell Daily Sun happened to feature an article about Helen Hamilton Gardener in 1927. When it was studied, her brain weighed in at 1,150 grams (approx. 2.5 pounds), around five ounces less than the average male brain. But this didn’t mean she wasn’t vindicated. “In the structure of her own brain Mrs. Gardener has presented abundant evidence that the brain of a woman need not be inferior to that of a man of equal rank,” the newspaper report proclaimed. Hers happened to weigh the same as that of esteemed anatomy and neurology professor at Cornell, Burt Green Wilder—the very founder of the brain collection itself.
Gardener’s point was made. Today it’s well established that brain size is related to body size. Paul Matthews, the head of brain sciences at Imperial College London, tells me, “If you correct for skull size, there are very tiny differences between the two sexes, but their brains are much more similar than they are different.” The missing five ounces are accounted for.
But that hasn’t stopped scientists, even today, combing brains for evidence that women think differently from men.
“Males will have an easier time seeing and doing.”
“When did you first become interested in studying sex differences?” I ask Ruben Gur, professor of psychology at the Perelman School of Medicine at the University of Pennsylvania. He pauses. “Since adolescence! Before that, I wasn’t that interested,” he jokes.
Ruben is one of two Gurs, the other being his collaborator and wife, Raquel Gur (a professor of psychiatry in the same school, who doesn’t respond to my request for an interview), who have dedicated their careers to understanding how the brains of women and men differ and what this means. Their first experiment in this niche was published in 1982, when Ruben Gur was thirty-five years old. Measuring blood flow through the brains of healthy people they found, to his surprise, that women had 15 to 20 percent higher flow rates than men. It was such an unexpected result, he tells me, that CNN was outside his lab the next morning for an interview.
This marked the start of a long string of headline-grabbing scientific publications. And their timing was perfect. In the 1970s sex difference research had experienced a decline because gender scholars and women’s rights campaigners argued that it was sexist to look for biological gaps between women and men, just as it was racist to look for differences between black and white people. Gradually, though, it became acceptable again. Neuroscience is a field in its infancy when judged by the task it has ahead of it. The brain is as dense and complex a thing as anyone has ever studied, with billions of nerve cells and an impossibly sophisticated web of connections between them. But understanding has recently been improved thanks to new imaging technologies, which allow scientists to understand brain activity in more detail than ever. These technologies have reinvigorated the search for difference. In 2006 the Gurs were invited to appear on the Today show to use one of these scanners to spot differences between the show’s medical editor’s brain and that of her husband.
Looking for sex differences in the brain isn’t just socially acceptable nowadays, it’s almost fashionable. “Back in 1982, we were lone wolves in the wilderness. Now everybody’s doing it!” laughs Ruben Gur.
What has changed since the nineteenth century, though, isn’t only the technology but also what we know about what’s inside our skulls. Researchers can no longer weigh or measure brains like lumps of coal, then assume this tells them something about human behavior or intellectual capability. “Of course the male brain looks more like the female brain than either of them look like the brain of another species,” Ruben Gur admits. But this similarity aside, he’s nevertheless convinced that women’s brains are different in a host of other ways, and that this in turn reveals something about how women think and behave. “The whole brain volume is in keeping with the body size, but the composition of tissue within the brain is different, with females having a higher percent of gray matter and men having higher percent of white matter,” he tells me.
Upon this observation lies the latest battleground in the gender wars. Having failed to show that brain size makes any difference, scientists like the Gurs have instead turned their attention to composition.
A cross-section of the human brain looks something like a freshly cut cauliflower. At the flowery ends are pinkish gray areas, known as the “gray matter.” This is what we generally think of as the energy-consuming workhorse part. In the gray matter, the bodies of brain cells translate chemical signals into electrical messages that can travel through the brain, helping it to take care of functions such as muscle control, seeing, hearing, remembering, speaking, and thinking. This is why people sometimes use the terms “brain” and “gray matter” interchangeably.
But there’s more to the brain than the tasty, flowery ends of the cauliflower. At the woody stems is the white matter, containing the thin, stringy tails of the brain cells, which make longer-distance connections to and from different parts of the brain. Using the connections in white matter to understand the brain’s architecture is a fairly new trend in neuroscience. It can be thought of as figuring out how a radio works not just by looking at the transistors but also by studying the wiring.
This work has been helped by a fairly new technique for scanning the brain, called “diffusion tensor imaging,” which allows researchers to picture the strength of the connections in these wires. Neuroscientist Paul Matthews at Imperial College London tells me, “It has completely changed the game, because it allows observations to be made at scale. You can look at the whole brain very rapidly.” Observations that would once have taken years can now be done in an afternoon. And it’s this technology that Ruben Gur and Raquel Gur, along with a large team of colleagues, used in an important study, published in the January 2014 issue of Proceedings of the National Academy of Sciences, looking at how women’s brains are wired differently from men’s.
Their paper stood out among the hundreds, even thousands, of studies into sex differences that get published every year. One reason for this was that the team studied a large group of people, almost a thousand, between the ages of eight and twenty-two. This size helped to lend it greater scientific value. Second, the findings were dramatic. A study he did in 1999, explains Ruben Gur, showed that in males, “a much higher percentage of the brain is devoted to white matter.” Meanwhile, “females have the same volume, or even greater volume, of corpus callosum, which is the largest body of white matter, the nerve fibers that connect the two hemispheres.” This new 2014 study went beyond volume to investigate the strength of the connections inside these two areas of white matter. And it seemed to confirm that men have more connections within the left and right halves of their brain, while women have more connections between the two of halves of their brain.
One popular feature of their research was the pictures. Their published paper was peppered with dazzling images of brains overlaid with blue, orange, green, and red lines to indicate how strong some of these pathways are. One image in particular, which has been reprinted by newspapers and websites all over the world, shows a male brain crisscrossed by blue lines within the hemispheres, and, beneath it, a female brain with orange zigzags showing a dense cluster of wiring between the two hemispheres. It made for perfect headline material, appearing to be nothing less than a literal representation of how differently the sexes think.
When the paper came out, the Atlantic magazine immediately declared, “Male and Female Brains Really Are Built Differently,” while the Telegraph newspaper, in the United Kingdom, announced, “Brains of men and women are poles apart.” Not entirely convinced, the online magazine the Register went with a tongue-in-cheek headline: “Women crap at parking: Official.”
What really captured the world’s attention was what the scientists suggested their data might tell us about how men and women behave. An earlier behavioral study the Gurs and their colleagues carried out on the same group of people, published in 2012, claimed to see “pronounced sex differences, with the females outperforming males on attention, word and face memory, and social cognition tests, and males performing better on spatial processing and motor and sensorimotor speed.” They argued that their new wiring diagrams, produced using the power of diffusion tensor imaging, could explain some of these differences.
“You need white matter in order to do spatial processing. It requires a lot of interconnectivity between regions to create a three-dimensional object and be able to rotate it in your mind in different directions,” explains Ruben Gur. This, apparently, is a feature of the male mind. “Males will have an easier time seeing and doing.” When I press him on what this means in practice, he tells me that they might react faster to what they see. For instance, if a man spots a lion about to attack, he might run away more promptly. In females, meanwhile, he sees links between the “verbal, analytic” parts of the brain and the “spatial, intuitive” parts. “I think, for women, they may have an easier time putting together their verbal thoughts with their intuition. If they are more intuitive, then they will be able to articulate the intuition better, at least to themselves,” he speculates a little vaguely.
At the time the paper was released, the media were aided by a press release sent out by the University of Pennsylvania’s medical school, designed to translate the findings into terms the public might better understand. This release made claims that went far beyond what the paper actually said. It stated that the brain-wiring differences shown by the Gurs and their colleagues indicate that men are better at carrying out a single task while women are better at multitasking. Ruben Gur himself admits to me that he hasn’t seen any scientific evidence to support this claim, and he’s not sure how it made it into the press release.
But at the time, when researchers spoke to reporters, they went even further. One of the paper’s coauthors, Ragini Verma, an associate professor working in biomedical image analysis at the University of Pennsylvania, told the Guardian, “I was surprised that it matched a lot of the stereotypes that we think we have in our heads.” She added, “Women are better at intuitive thinking. Women are better at remembering things. When you talk, women are more emotionally involved—they will listen more.” She told the Independent, “Intuition is thinking without thinking. It’s what people call gut feelings. Women tend to be better than men at these kinds of skill which are linked with being good mothers.”
Characterizing the sexes in this way is sometimes euphemistically phrased as women and men “complementing” each other. Different but equal. They’re useful in their own ways, just not at the same things. It’s an idea that runs through some religious texts, but was also popular during the Enlightenment in Europe, as thinkers then grappled with how a woman’s role in society should be defined. The eighteenth-century French philosopher Jean-Jacques Rousseau was among many intellectuals—male and female—who argued against women’s equality on the basis that they weren’t the same physically or mentally, but each designed for their own separate spheres. The notion of complementarity thrived through to the Victorian era and ultimately became epitomized in the 1950s middle-class suburban housewife. She fulfilled her natural role as wife and mother, while her husband fulfilled his role as breadwinner.
According to Ruben Gur, his findings reinforce this idea that women complement men. “I’m impressed by the complementarity between the sexes,” he replies, when I question him on what his results tell us about the brain. “It almost looks like what is strong in one sex will be weaker in the other and whatever that difference is in the other sex you’ll find a complementary effect in the other. Biologically, we are built to complement each other.”
“I think they have a particular mission.”
“This is an eighteenth-, nineteenth-century problem. We really shouldn’t be talking in these terms. I don’t know why we’re still doing it,” complains Gina Rippon, professor of cognitive neuroimaging at Aston University in Birmingham in the United Kingdom. Her long, narrow office, in what proudly claims to be one of the biggest freestanding brick buildings in Europe, is scattered with books on neuroscience and gender. On the shelf are a couple of tiny replica brains and a white coffee cup shaped like a skull. She is one of a small but growing number of neuroscientists, psychologists, and gender experts scattered across the world who are desperately batting away claims that brains show significant sex differences. In the twenty-first century, she is fighting Helen Hamilton Gardener’s old war.
Rippon became interested in sex and gender when she was teaching courses on women and mental health at the University of Warwick, where she spent twenty-five years at the start of her career. More women than men tend to suffer from depression or have eating disorders, and she found that, time and again, their illnesses were being explained as something innate to them as females that made them vulnerable. She was instead convinced that there were stronger social reasons for their mental problems. This sparked a fascination with how biological explanations are used and misused, particularly when it comes to women.
“That’s the point I was called a feminist biologist,” Rippon tells me.
When she arrived at Aston University in 2000 and started working in neuroimaging, she decided to take a look at how the latest powerful imaging techniques were being used in research on women. Technologies like electroencephalography had already been used for almost a century to study electrical signals in the brain. But during the 1990s, functional magnetic resonance imaging—a technique that allows researchers to track changes in brain activity by measuring which areas see more blood flow—utterly transformed the field. There was an explosion of new studies, many of which came tagged with eye-catchingly colorful pictures of the brain.
With this, Paul Matthews of Imperial College London informs me, “cognitive neuroscience was born.” It became the most popular way of watching what happens to brain activity when people carry out different tasks or experience emotions.
Despite the promise of this new technology, however, the pictures it painted weren’t always pretty. Especially for women. “I did a review in 2008 of where we were going with the emerging brain imaging story and gender differences, and I was horrified,” says Rippon. Studies, including some carried out by Ruben Gur at the University of Pennsylvania, saw sex differences in the brain when it came to almost everything. Examples included verbal and spatial tasks, listening to someone read, responding to psychological stress, experiencing emotion, eating chocolate, looking at erotic photos, and even smelling. One claimed that the brains of homosexual men had more in common with the brains of straight women than straight men.
“I just got drawn into it because I thought this is horrendous, that it is being used in exactly the same way as people in the past saying women shouldn’t go to university because it will mess up their reproductive systems,” she tells me.
Rippon wasn’t the only one raising her eyebrows at some of these brain studies. Functional magnetic resonance imaging produces pictures that can be easily skewed by noise and false positives. The best resolution it can reach is a cubic millimeter or so, and with many machines, it’s considerably less. This may sound like a tiny volume, but is in fact vast when it comes to an organ as dense as the brain. Just one cubic millimeter can contain around a hundred thousand nerve cells and a billion connections. Given these limitations, people inside the scientific community began to be concerned that they might be reading too much into brain scans.
All over the world, what started as quiet criticism became a crescendo. In 2005 Craig Bennett, then a first year graduate student at Dartmouth College in New Hampshire, carried out an equipment test that inadvertently revealed how it might be possible to read just about anything into a brain scan. He and a colleague tried to find the most unusual objects they could fit inside a functional magnetic resonance imaging machine, to help calibrate it before their serious scientific work began. It was a joke that started with a pumpkin and ended with a dead, eighteen-inch-long, mature Atlantic salmon wrapped in plastic. A few years later, when Bennett was looking for evidence of false positives in brain imaging, he dug out this old scan of the salmon. By chance, proving the critics right and showing how even the best technologies can mislead, the picture happened to show three small red areas of activity close together in the middle of the fish’s brain. The dead fish’s brain.
Amusing though the salmon experiment was, it highlighted what some saw as a far more serious problem in neuroscience. Eight years after Bennett’s fish trick, the journal Nature Reviews Neuroscience published an analysis of neuroscience studies and reached the damning verdict that questionable research practices were leading to unreliable results. “It has been claimed and demonstrated that many (and possibly most) of the conclusions drawn from biomedical research are probably false,” the article began.
The authors explained that one big complication is that scientists are under enormous pressure to publish their work, and journals tend to publish results that are statistically significant. If there’s no big effect, a journal is less likely to be interested. “As a consequence, researchers have strong incentives to engage in research practices that make their findings publishable quickly, even if those practices reduce the likelihood that the findings reflect a true. . .effect,” they continued. They pointed out that “low statistical power” was an “endemic problem” in neuroscience. In summary, scientists were being pressured to do bad research, including using small samples of people or magnifying real effects, so they could appear to have sexy results.
Paul Matthews, a highly respected British neuroscientist, admits that in the early days of functional magnetic resonance imaging, many researchers—himself included—were caught out by unintentionally bad interpretations of data. “The errors that have been made have been fundamental statistical errors. We’ve all made them,” he says. “I’m more careful about it now, but I’ve made them, too. It’s a very embarrassing thing. It’s born of this strong drive to derive results from whatever works one’s completed, because one can’t do anymore. . . . Most people, if not the overwhelming majority, don’t intend to cheat. What they try to do is get excited because of exploration, and they misstate the degree to which they’re exploring the data or the meaningfulness of the exploratory outcomes.”
The problem has at least been recognized. Even so, Gina Rippon believes that sex difference research continues to suffer from bad research because it remains such a hot-button topic. For scientists and journals, a sexy study on sex difference can equal instant global publicity.
The vast majority of experiments and studies show no sex difference, she adds. But they’re not the ones that get published. “I describe this as an iceberg. You get the bit above the water, which is the smallest but most visible part, because it’s easy to get studies published in this area. But then there’s this huge amount under the water where people haven’t found any differences,” Rippon explains. People end up seeing only the tip of the iceberg—the studies that reinforce sex differences.
Ruben Gur and Raquel Gur have contributed a sizeable chunk of work to the visible tip of the iceberg, she says. “I think they have a particular mission.”
In her 2010 book Delusions of Gender, psychologist Cordelia Fine coins the term “neurosexism” to describe scientific studies that fall back on gender stereotypes, even when these underlying stereotypes are themselves unproven. Ruben Gur’s 2014 study on sex differences in white matter between men and women, Gina Rippon tells me, is among those that deserve to be described as “extremely neurosexist.”
“Ruben Gur’s lifelong passion is to investigate, enumerate, identify, and prove that there are sex differences in the brain,” she continues. “A very strong belief in psychological sex differences and explaining them in terms of brain characteristics. That’s his life’s work, and his lab is still producing that material. It’s an impressive body of work, but it’s not until you start drilling down into it, in quite an arcane fashion in some cases, that you see that actually some of it is quite flawed.”
Critics have questioned, for instance, the Gurs’ underlying assumption that men and women perform differently when it comes to social cognition tests, spatial processing, and motor speed. Study after study has shown almost all behavioral and psychological differences between the sexes to be small or nonexistent. Cambridge University psychologist Melissa Hines and others have repeatedly demonstrated that boys and girls have little, if any, noticeable gaps between them when it comes to fine motor skills, spatial visualization, mathematics ability, and verbal fluency.
When it comes to the paper on white matter, Rippon explains, every sex difference that Ruben Gur and his colleagues claim to see can be accounted for by the fact that men have a larger body size and brain volume. As the brain gets bigger, other areas have to get bigger too, in different proportions depending on what’s important to keep the brain functioning normally. “If you look at it as a scaling problem, the gray and white matter will change as a function of the brain size, so even that is to do with size.”
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.”
Researchers rarely look at the brain in this way. Very often they’re studying just one brain region, like the amygdala or hippocampus, or one particular behavior, like mathematical ability or watching porn. Looking at the brain and behavior as a whole produces very different results when it comes to sex difference. Joel’s research reveals that, depending on the study, between 23 and 53 percent of people show variability in their brains, with features associated with both men and women. Meanwhile, the proportion of people in the studies she has analyzed that have purely masculine or purely feminine brain features is between none and 8 percent.
“If you take any two brains, they are different, but how they differ between any two individuals, you cannot predict,” she explains. By this logic, there can’t be any such thing as an average male or average female brain. We are all, each one of us, a mix. Our brains are intersex.
Having the fresh perspective of female researchers like Gina Rippon, Anne Fausto-Sterling, Melissa Hines, Cordelia Fine, and Daphna Joel—while it may not immediately change how science tackles sex difference—may at least force a rethink of old beliefs that women’s minds must be essentially different from men’s because the only alternative would be that they’re identical. They take the black and white divisions of the past and reveal that the truth is more likely to be gray.
Anne Jaap Jacobson, a philosopher and emeritus professor at the University of California, Berkeley, now based at the University of Houston, has coined the word neurofeminism to describe this alternative approach to brain science, which attempts to root out stereotypes and look at brains objectively. “A lot of the research starts off with the assumption that various people call ‘essentialism.’ That men and women are essentially different, that the differences are really sort of basic,” she tells me.
“The problem with this question of difference and similarity is that we’re all different and we’re all similar,” explains Daphna Joel. “When people want to study sex in the brain, they immediately translate this to studying sex differences. But already here they make many assumptions, and the first is that there are two populations of brains, male and female. This is an assumption that needs to be shown scientifically, or proven. They say: ‘This is solid ground, and from here I continue.’ I question the solid ground.”
Neuroscientist Paul Matthews agrees that this approach could be a useful corrective for neuroscience. “Comparing males and females at any one time point is a complicated question to make meaningful, because it is actually so ill-defined as posed,” he says. “There’s a lot of variability in individual brains. In fact, the anatomical variability is much greater than we ever realized before. So the notion that all people of the male sex have a brain that has fixed characteristics that are invariant seems less likely to me. In fact, so much less likely that I think the notion of trying to characterize parts of the brain as more male-like or more female-like actually isn’t useful.”
Ruben Gur, while he refuses to shift in his conviction that sex differences in the brain are the rule rather than the exception, admits to me that these days he has changed the language he uses. “A lot of people are using the term ‘sexual dimorphism’ when they talk about sex differences in brain structure, and I’m guilty of that myself,” he says. “I’ve done that, but I don’t do that anymore. Because if you think of it, when you talk about dimorphism, you’re really talking about sexual dimorphism. You’re talking about different forms. So a penis versus the vagina, that’s a sexual dimorphism. Having breasts is a dimorphism. I wouldn’t go so far as saying the brain is dimorphic. I would say there are some significant differences, sex differences, in brain anatomy, but I wouldn’t say they rise to the level of being dimorphic.”
All this work on sex difference in our bodies and brains has a story underneath it.
When neuroscientists like Ruben Gur and Simon Baron-Cohen claim to see profound gaps between women and men, they are aware that these gaps aren’t spontaneous. If they’re there, they’re there for a reason. Gur has described them as revealing how we are “built to complement each other,” suggesting that humans must have evolved with some sexual division of labor between them. Women, he implies, are the more empathic, intuitive sex, perhaps built for parenting. Men are better at seeing and doing, he says, which seems to suggest they are the natural hunters and builders. Baron-Cohen also argues that men tend to be the systemizers while women are the empathizers.
“If your job is to lift a hundred and fifty pounds, and you can’t do it, why should you want to work in that job?” Gur asks me.
It’s hard to argue with that kind of logic. But while he’s willing to speculate on what biology tells us women have evolved to be able to do, it’s a question that’s beyond his job description. It belongs to the field of evolutionary biology.
The evolutionary perspective reminds us that our bodies weren’t created yesterday. They were forged over millennia, every part slowly adapting to the pressures of the environment to better serve some need. From breasts and vaginas to brain structure and cognitive ability, for every difference or similarity we see, there must be some evolutionary purpose to it. This is where the sex differences and similarities that biologists claim to see in our bodies and brains connect with the story of our past. If women are better survivors than men, the explanation for it is in this tale. If women and men have quite similar brains, the reasons for that are here, too.
Evolutionary biologists have the almost impossible task of deciphering this story. Did the sexes complement each other, the way Ruben Gur suggests, or did they do the same jobs and share parenting? Were women crouched around a campfire, tending to children and waiting for male hunters to bring home the bacon? Were they independent, hunting for their own food? Were they monogamous or promiscuous? Were males always dominant over females?
They are questions that science may never fully answer, but there are ways to try. One window on the past is provided by primatologists studying our closest animal cousins, the great apes, from whom humans split around five million years ago. Studying how they interact gives us some insight into what our basic way of life may have been before we became the species we are now. Another window comes from evolutionary psychologists, who try to picture life in the Pleistocene, the epoch during which modern humans evolved looking anatomically the way we do now. Then there’s archaeological evidence, such as tools and bones. By observing the lives of modern-day hunter-gatherers, anthropologists can also draw portraits of how early woman might have lived.
Writing our evolutionary story isn’t easy and it’s also plagued by controversy. As Charles Darwin’s work in the nineteenth century proves, the narratives have often been shaped by the attitudes of the time. Even he, the father of evolutionary biology, was so affected by a culture of sexism that he believed women to be the intellectually inferior sex. It’s taken a century for researchers to overturn these old ideas and attempt to rewrite this flawed tale.