by Angela Saini
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 thriv
ed 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.”