Essay of the week: Mars to Venus – is there really no difference between male and female brains?

We have, of course, come a long way since Victorian scientists attributed women’s “intellectual inferiority” to the “missing five ounces of the female brain”. But the brain remains a key battle site in the controversy over gender. What science tells us about it matters since it drives attitudes. For instance, the idea that boys and girls learn very differently has driven a movement for same-sex schools in the United States. And the idea that girls are biologically more inclined towards caring and empathy, and boys more interested in how things work, fuel the stark division of infant toys that will result in pink-filled stockings for girls this Christmas, and blue-filled stockings for boys.

So the recent publication of a study of MRI scans which show no inherent difference between male and female brains, represents a significant shift in the way we talk about gender. According to the project's lead researcher, Professor Daphna Joel, our brains are a “shifting mosaic” of features, some more common in females compared to males, some more common in males compared to females, and some common in both.

This mosaic metaphor chimes with our times. Many of us feel as if we are a mish-mash of characteristics and tendencies that belong to this traditional gender stereotype or that. I am good at fixing things, but bad at throwing a ball. My husband is great at parking a car, but appears befuddled by technology.

When I ask my eight-year-old son if he thinks girls’ brains are different from boys’, he looks puzzled. “I thought all brains were different,” he says.

Writing in The Guardian last week, neuroscientist Cordelia Fine, author of Delusions Of Gender, jubilantly declared that Joel’s research put a nail in the coffin of the persistent view that “there are female and male natures subserved by a ‘female brain’ and a ‘male brain’, respectively”. She pointed out that there is little link between having one stereotypically female characteristic and others. “Research shows,” she wrote, “that correlations between 'masculine' traits are weak or non-existent; so too for 'feminine' traits. Having one doesn’t imply you have another. For example, being gentle doesn’t imply that one is also dependent.”

All this is nothing new to many of us. In a survey, 41% of British people said gender was a social construct (though 36% opposed that view). Indeed, a small but growing number of people are refusing the labels "male" or "female" altogether, and describing themselves as "non-binary" or "gender-fluid". Last year the Scottish Transgender Alliance launched a campaign for the recognition of a third gender, which they said should be available to people who have a non-binary gender identity.

The idea that there is such a thing as a male brain and female brain has, however, been persistent in recent history. Books like The Female Brain by Louann Brizendine, or Simon Baron-Cohen’s The Essential Difference have driven home a message that the brain disparities between the sexes are profound. Baron-Cohen has built a popular following for his view that women are predominantly empathisers, men mostly systemisers, and the extreme male brain is an autistic one.

Of course, you can be a man with a female brain and vice-versa. Earlier this year, in an article promoting a BBC Horizon programme, The Daily Mail offered readers a series of tests supposedly determining whether their brains were male or female. One concerned which thumb you put on top of the others when your fingers interlocked; another asked which emotions were triggered by a series of photographs of eyes. My own results showed that I have a male brain, not a female one. Yet I am a woman.

The notion that when it comes to the way they think, Men Are From Mars And Women Are From Venus, has long been a big seller when it comes to popular nonfiction: a tradition that stretches back to John Gray’s classic book and beyond. The media is persistently riddled with male brain/female brain stories. Three years ago, researchers at the University of Pennsylvania, said the neurons within men’s brains were connected to each other in a very different way from the neurons in women’s brains. A more recent study found that those with so-called male brains have higher salaries than those with female brains.

But increasingly, media outlets have been publishing studies that contradict that idea. Last year, research found that caring for children awakens a parenting network in the brain – even turning on some of the same circuits in men as it does in women, and suggesting that the underpinnings of the so-called maternal instinct aren’t confined to women.

Previously, Rochester University researchers, Bobbi J Carothers and Harry T Reis, had found that “Men are from Earth, women are from Earth.” When they analysed data from 13 different studies, looking for sex differences, they found that outside “stereotypic activities, such as scrapbooking and cosmetics (women) and boxing and watching pornography (men)” there was no distinct gender difference. As they reported: “No matter how strange and inscrutable your partner may seem, their gender is probably only a small part of the problem.”

Discoveries being made about sex at a genetic and chromosomal level are also part of this story. At no level is the boundary between the genders a strict, unperforated line, and biologists are more aware of this than anyone. There are, for instance, people who are chimeras, whose bodies are built from the cells of two individuals, probably twin embryos, whose bodies may be part male, part female. Some researchers say that as many one person in 100 could have some form of sex development disorder, making them in some way intersex.

But it’s not only at a genetic level that sex is complex. Research has found that when a female baby is exposed to the masculinising effects of high testosterone in maternal blood, she is likely to exhibit more stereotypically masculine traits in adult life.

What is striking though is that, in recent years, there has been an increasing trend towards popular books disputing brain sex difference. It’s as if a substantial section of society, fed up with the polarising, "pink for girls, blue for boys" dichotomy, is developing an appetite for science and literature that allows us a glimpse beyond this gender prison. Among the scientists at the cutting edge of this work are Cordelia Fine, and neuroscientist Lise Eliot, author of Pink Brain, Blue Brain. Both try to unpick the assumptions made in much sex-difference research, and the popular science literature it has spawned. They aren’t saying there is no biological difference. Eliot says that, yes, “boys and girls are different”, though she maintains that most psychological sex differences “are not especially large”. “Genes and hormones light the spark,” she writes, “for most boy-girl differences, but the flame is strongly fanned by the essentially separate cultures in which boys and girls grow up.”

When it comes to the brain/gender issue, science seems to have become increasingly divided, split along heated ideological lines between those sometimes described as “anti-sex difference” (Fine, Eliot, Daphna Joel) and those involved in the thriving field of “sex-difference research” (Larry Cahill, Melissa Hines). However, no-one in the field of science appears to believe that sex has no impact on the brain whatsoever.

Last year, Larry Cahill, a neurobiologist at University of California, accused “anti-sex difference” researchers of “operating from a deeply ingrained, implicit, false assumption that if men and women are equal, then men and women must be the same”. Cahill wrote of a growing counter-reaction to sex-difference research which he said was “based on a misunderstanding of some key facts of brain biology”, and dismissed “the psychologist who calls people studying brain-sex differences neurosexists" [Cordelia Fine] as “a namecaller”. He proceeded to cite various pieces of research as evidence of significant difference between the sexes on certain traits. His essential message was that women and men are not the same, and that we shouldn't try to deal with them as such, particularly when it comes to medication and health treatment. “The truth is that of course men and women are equal (all human beings are equal),” he writes, “but this does not mean that they are, on average, the same. And, in fact, if two groups really are different on average in some respect, but they are being treated the same, then they are not being treated equally on average.”

Among the theories Cahill criticised was the "mosaic brain" model touted by Daphna Joel. While he conceded that Joel was correct in pointing out that “both males and females are exposed to both masculinising and feminising influences”, he questioned her conclusion, that we all have “an intersex brain (a mosaic of 'male' and 'female' brain characteristics)” .

Her “unisex view,” he wrote “fails to accommodate a host of facts ... such as dyslexia’s incidence in up to 10 times as many males as females ... We aren’t unisex, and every cell in the brain of every man and every woman knows it”.

Needless to say the “name-callers” and “anti-sex difference researchers” reacted, declaring their concern that the mistake of treating males as the norm will be “replaced with another, namely, treating males and females as two distinct entities”. They point out that there is “growing evidence that thinking about the brains and behaviour of males and females in this inappropriately categorical way has psychosocial effects that serve to sustain the gender status quo”.

Certainly that status quo seems to have us in a firm grip. Anyone looking for evidence of a profound difference between boys and girls from an early age could find it in the world around them, the young children they see, and in the Channel 4 series, The Secret Life Of 4, 5 and 6 Year Olds. Boys like rough play. Girls are further ahead in their linguistic skills than boys of that age. Girls like kiss-chase. Boys want to be leaders.

But what does that ultimately tell us? Often, as Fine and Eliot point out, parents assume because they’ve vaguely tried to treat their boy and girl children the same, or attempted to buy a few trucks for their daughter or dolls for their boy, that whatever gender stereotypical behaviour their children exhibit is biology fighting its way through. But, in a world where the first thing we like to know about a baby is whether it’s a boy or a girl, our children are receiving gender cues from the moment of birth. We may think we behave no differently with boy babies than girl babies, but we are wrong. Experiments have shown that girls disguised as boys are more likely to be perceived as angry or distressed; boys disguised as girls tend to be perceived as happy and socially engaged.

The truth is, we don’t yet know how much of gender is culture, how much biological, and whether the latter leads the former. All we know is that there are two things here: one the social construct of gender; the other biology, what we are made of, what we start out with and how that develops.

Yet the idea that there is a female brain and a male brain remains so powerful that it is a barrier to our understanding of the real complexities of the way sex works within our bodies, and a distorting factor in our personal lives, causing us to blame gender when really what may be at fault is our relationship with a particular human being.

Gradually though, this pink brain, blue brain story of human identity is beginning to disintegrate. That’s not to say that anyone is declaring that sex difference doesn’t exist, or doesn’t have a role to play in some elements of who we are, but it’s much more complex than is often presented, and the truth is far from being simply that we are two distinct biological systems primed for two very different roles.

What does that mean for us? Perhaps that a third gender, a non-binary category for human identity, should be welcomed. Or perhaps simply that we should stop making gender the fundamental marker of who they are, cease putting the sex box at the top of all but health forms, resist making the first question we ask a new parent whether their baby is a boy or a girl.