Arianne Shahvisi · What’s the difference? Sex in the Brain · LRB 8 September 2022 – London Review of Books

As a teenager,​
 I couldn’t find anyone to play chess with me, so I pored over a small yellow copy of Chess Made Easy and set up games against myself. Mine is the 26th edition of Cecil Purdy and Gary Koshnitsky’s primer, first published in 1942. Returning to it recently, I noticed a brief section towards the end on ‘Women in Chess’. It is often the case, the text notes, that when a husband and wife learn to play together, ‘the wife wins a majority of their games.’ One anticipates an adversative conjunction followed by some folk sexism to dash the hopes of a girl improver. Instead, there’s this:

Competitive chess is a different story. One basic reason may be that a woman’s time tends to be cut into more. But mainly it’s just fashion and tradition. Young girls generally just don’t study chess seriously, as many boys do. The very few who do so have considerable success.

A pocket book on chess isn’t the first place you’d look for an elegant nod to the effects of gender socialisation and the fragmentation of women’s leisure time. When asked, in 1963, about the obvious disparity in the game, Bobby Fischer said of women: ‘I guess they’re just not so smart.’ In 1989, Garry Kasparov insisted that chess ‘does not fit women properly. It’s a fight, you know? A big fight … Women are weaker fighters.’ (When he was reminded of these comments after Judit Polgár beat him in 2002, he said: ‘I don’t believe that now.’)

No woman has ever been world chess champion. Probabilistic effects are sufficient explanation for this – fewer women ‘study chess seriously’, so the pool of potential champions is much smaller – but ‘stereotype threat’ is also implicated. A study from 2007 showed that women play as well as men in online chess games provided they don’t know the gender of their opponent. Their performance suffers when they are told they’re facing a man and improves if they think they’re up against another woman, regardless of their opponent’s actual gender.

The British grandmaster Nigel Short wrote in 2015 that men are ‘hardwired’ to play better chess, and later tweeted ‘Men and women do have different brains. This is a biological fact.’ (Short too was defeated by Polgár, but evidently it didn’t do him any good.) That view isn’t borne out by a recent meta-analysis covering three decades of studies, which concluded that there is no evidence for sex dimorphism in the human brain once differences in size are accounted for. The brains of male humans are, on average, 11 per cent larger than those of females. They also have a higher proportion of white matter (so called because of the fatty white sheaths of myelin that provide electrical insulation to nerve fibres), since bigger systems require heftier infrastructure to transmit the same signal over longer distances. But this tells us next to nothing. Absolute brain size does not indicate greater intelligence: horses are not as clever as chimpanzees. Brains scale with body size, regardless of sex or species. When the average sizes of organs are compared by sex, there is a greater difference between lungs, livers, hearts and thyroids than there is between human brains.

Yet the belief persists that there are innate brain differences between the sexes. As the neuroscientist Gina Rippon writes in The Gendered Brain, dealing with the myths of ‘neurosexism’ is like playing ‘whack-a-mole’: each time you smack one down, more spring up elsewhere. Why are these myths so tenacious? For a start, findings are often based on small sample sizes, or observed effects are overblown. There are also reporting biases, the most obvious of which is the ‘file drawer effect’. Studies that discover differences between the sexes are readily submitted for publication, while those that don’t tend to be filed away. Observations of similarity therefore go underreported, and accounts of brain sex dimorphism are less likely to be undermined by research that fails to replicate their findings. As the psychologist Gerald Haeffel put it in a Royal Society paper published in June, ‘Psychological science is on an extraordinary winning streak. A review of the published literature shows that nearly all study hypotheses are supported. This means that either all the theories are correct, or the literature is biased towards positive findings.’

Science writers and journalists play their part in the myth-making. When they announce evidence of brain sex differences, they often omit to mention that the resounding effect relates to zebra finches or prairie voles, or – when the evidence is human – that the participants’ average age was sixty, so that scientists were scanning brains that had undergone the best part of a lifetime’s influences. Researchers and reporters know what they’re doing: sexism sells. There is an appetite for science that legitimises our prejudices. Perhaps there’s some version of the just-world hypothesis at work: my not being good at chess is less vexing if I can blame it on the sex limitations of my brain, rather than the competing demands on my time, the undermining effects of stereotypes, or my laziness. Or maybe it’s easier to digest simple explanations for troubling phenomena. Why grapple with the complex confluence of bodies and cultures when you can settle for believing that sex differences are rooted in our genes or in the lives of our ancient ancestors? Rippon mentions a paper whose authors attempt to trace the gendering of pink and blue to our evolutionary origins. Their conclusion is even sillier than the premise: food-gathering cavewomen had to be able to pick out blushing berries; cavemen hunters were adapted to scan the horizon against a blue sky.

Writing in the New Humanist in 2009, Raymond Tallis advised: ‘If you come across a new discipline with the prefix “neuro” and it is not to do with the nervous system itself, switch on your bullshit detector. If it has society in its sights, reach for your gun.’ There is now a whole genre of popular science devoted to debunking the neuroscience of sex differences. This sometimes results in a stodgy, carping sort of writing, and one wonders how many minds are actually changed by it, but as long as the ‘neurotrash’ piles up, it is important to have patient, conscientious rebuttals on the record. Rippon, in her comprehensive book, doesn’t reject the possibility of brain sex differences outright, but instead shows that tugging at the thread of most of the claims in circulation reveals a gendered origin story. Male infants walk earlier, but do so after greater motor encouragement; female infants talk earlier, but are usually spoken to more. Men tend to outperform women on ‘mental rotation’ tasks, that is, when visualising the way an object would appear from a different vantage point. But the difference isn’t observed in young children and is more reliably correlated with time spent playing computer games: it’s less a question of neuroanatomy than of who has a Nintendo. A survey of a million people across 48 countries, published in 2015, indicated that women have significantly lower self-esteem than men. In trying to account for that striking finding, you can either choose to probe the brain’s self-evaluation centres and tell just-so stories about archaic humans, or you can take seriously the fact that every culture has ways of making women feel bad about themselves.

When we scour brains for signs of sex, we’re bound instead to find the imprints of gender. And unless we’re careful, we’re apt to mistake one for the other. If there are primordial sex differences, we have spoiled our chances of finding them: sexism not only changes our brains, it also tends to blunt the objectivity that’s needed to do good science. Maybe some of us are innately worse at chess, or maths, or mental rotation tasks, but stereotypes and material barriers set far lower ceilings than biology does. To accept this means starting our inquiry from a different point. In her recent book The Disordered Cosmos, the cosmologist Chanda Prescod-Weinstein asks: ‘What are the conditions we need so that a 13-year-old Black kid and their single mom can go look at a dark night sky, away from artificial lights, and know what they are seeing? What healthcare structures, what food and housing security are needed?’* Most brains are good enough for most things; the problem is that too many are underfed, sunk in cortisol, hemmed in by stereotypes and taken up with the demands of survival. Prescod-Weinstein’s words echo those of Stephen Jay Gould forty years ago: ‘I am, somehow, less interested in the weight and convolutions of Einstein’s brain than in the near certainty that people of equal talent have lived and died in cotton fields and sweatshops.’

Studies of sex in the brain are also beset with terminological difficulties. Researchers rarely specify what they mean by ‘sex’, and most rely on participants’ self-reporting of their gender. What, then, are they actually studying? I’m reminded of science classes at school, in which we were assured that electrons orbit the nucleus of an atom at set distances, like planets. Those who carry on with physics or chemistry discover they were lied to: not only are those clean orbitals in fact fuzzy balloons of probability, but electrons are not in those clouds, they are the clouds. The half-truth prepares you for a knottier reality. Understanding sex and gender requires a similar pedagogical manoeuvre. The usual simplification prises sex and gender apart with the mantra ‘Sex is biological; gender is social.’ By those lights, hairdressers’ should really be ‘unigender’, not ‘unisex’; and a ‘gender reveal’ party should really be a ‘genital reveal’ party (it’s unclear whether this is an error, a euphemism, or both) – foetuses don’t have genders any more than they have accents or handwriting. The mix-up is common even among experts: more than a hundred biomedical papers in the last five years claim to be studies of ‘foetal gender’.

The truth is that sex and gender aren’t so easily divided. One appears to be grounded in hard biological facts, while the other rests on the seemingly slippery notion of identity. Yet most of us have a much firmer grip on gender than we do on sex. Gender is an observable part of our everyday world, while the decisiveness of sex is mostly taken on trust. The US army confidently defines biological sex as ‘a person’s biological status as male or female based on chromosomes, gonads, hormones and genitals’. But the four things don’t come as a multipack, and no single one of them supplies the basis for a clean binary opposition between the sexes. Some elite athletes, obliged to submit to dubious, prurient and often racist testing regimes, have been told that while they have the ‘right’ genitals for their competitive category, they have the ‘wrong’ hormone levels or chromosomes. Which bit tells us the truth about sex? Professional sport has always been a peculiar business of seeing what atypical bodies can do when subject to atypical forms of conditioning. The continual gerrymandering of the line that promises to divide the sexes only emphasises the absurdity of the exercise.

‘Gender critical feminists’ adopt a strategic simplicity, describing women as ‘adult human females’, most often defined by their possession of a uterus, or of the right genitals. Penises are associated with sexual assault and vaginas with sexual vulnerability, which sets up exactly the sort of fairy-tale fear-mongering that puts them in league with the far right. Theirs is, as Judith Butler writes, ‘a rich fantasy, and one that comes from powerful fears, but it does not describe a social reality’. Trans women are more likely to be sexually assaulted than cis women, and vulnerability to violence is, for most women, a more concrete definition of what unites and constrains us. Though they might reject the terms of the question, those intent on excluding trans women from their concerns must reflect on some version of Audre Lorde’s challenge: ‘What woman here is so enamoured of her own oppression that she cannot see her heel-print on another woman’s face?’

Others take the gold standard for the identification of sex to be chromosomes – incontrovertible evidence, written into the very code of our cells, of who each of us really is. Yet most of us will never know anything of our chromosomes. (A study published in June, based on UK Biobank data, estimated that as many as one in five hundred men might have an extra X or Y chromosome.) We know even less of the chromosomes, gonads, hormones and genitals of others. What we register are hair and clothes and whatever can be discerned of fat and muscles. Almost all of these markers are readily modified through dieting, exercise, depilation, surgery, hormones and make-up. We interpret differences that have been contrived or magnified through techniques of gender as differences attributable to sex.

Sex chromosomes​ are life-shaping, but not in the ways one might assume. The geneticist Sharon Moalem, in The Better Half, argues that what matters is whether or not your parents pass on to you the genetic equivalent of belt and braces. ‘Females’ are homogametic: they have two X chromosomes, one from each parent. ‘Males’ are heterogametic: they have one X chromosome and one Y chromosome.† (In birds, this is reversed: male birds are homogametic and females heterogametic.) An X chromosome hosts eight hundred or so protein-coding genes, while a Y chromosome has just seventy. Each human cell needs to use the genetic material on one X chromosome. Where there are two, one X is silenced and the other left active. This selection is made early in embryonic development, and different cells make different choices. Until recently, it was believed that X-inactivation was complete and permanent, but in fact around a quarter of genes on the ‘silenced’ X escape inactivation and remain available to the cell. Homogametic beings are therefore left with a wide and responsive armoury of genetic resources. When exposed to threats, heterogametic beings have just one set of genetic tools. That’s fine if those genes are up to the challenge, and potentially disastrous if not. For those with two X chromosomes, the auxiliary set of genes offers a back-up plan.

Moalem shows that genetic redundancy confers an advantage on around half of us when it comes, among other things, to immunological brawn, averting developmental abnormalities and colour vision. Crucially, a set of six genes that are important for the suppression of cancerous tumours are among those able to escape X-inactivation. A single mutation on one X chromosome can turn off a tumour-suppressing gene, leaving a person more vulnerable to a range of cancers, but in those with a second X, these ‘escape’ genes remain functional. Such variations may explain the striking difference in longevity between the sexes. At birth, there are 105 heterogametic for every hundred homogametic babies, but by age forty males have lost their majority. Females make up 80 per cent of those who live to one hundred, and 95 per cent of supercentenarians. Heterogametic immune systems are apt to be overly enthusiastic (‘self-critical’, as Moalem puts it), leading to higher rates of autoimmune disease as bodies turn on themselves.

Moalem’s work has serious consequences for health research, but it isn’t concerned with the social meanings of sex. Rippon reserves the most glaring area of contention for a few paragraphs at the end of her book. If there are no ‘male’ and ‘female’ brains, how should we understand the mismatch between identity and the body articulated by many transgender people? That would seem to require that we speak of a brain that is oriented differently from its body, i.e. a brain that is sexed. Rippon’s gloss echoes the ‘colour-blind’ response to racism: ‘Perhaps we should be challenging the concept of any kind of pre-labelled box into which human beings are slotted?’ The boxes are certainly a problem. But she makes the mistake – often made in relation to sex work – of confusing one potential (or utopian) goal with what is fair in the present. Wanting a world without inflexible gender categories shouldn’t require that the people harmed by those categories be sacrificed to the cause. People have to live in their bodies. And we’ll sooner break or escape the boxes by cheering acts of subversion than by wishing the boxes away.

What’s more, being sceptical of sex differences doesn’t detract from the fact that brains are diverse along many other axes, and can relate to their bodies in ways that chafe against the world’s expectations. Maybe it’s nature, maybe it’s nurture; probably there will never be a useful way of cleaving one from the other. Perhaps we should just concede that we don’t know what makes trans people trans any more than we know what makes gay people gay, and that there can be something suspect in needing to know, rather than being ready simply to accept.

One of the many contradictions of these discussions is that those intent on finding and policing binaries are often resistant to the idea of broader forms of diversity. There are, after all, a great many differences between us. Some of us are much more vulnerable to sexual violence than others. Some of us are more likely to have our time cut into. Some of us are given games consoles, forgiven for long absences while we are at play and become freakishly good at mental rotation tasks. Some of us have our labour devalued and our ideas stolen. Some of us have more robust genetic resources. Some of us are able to become pregnant and are at risk of having our futures held hostage to that fact. Each of these differences matters, and at any moment might be the locus of a definition or a demand. These differences are also connected, but not by our biology so much as by the political and economic roles in which we have been cast. ‘Male dominant society has defined women as a discrete biological group for ever,’ Catherine MacKinnon said in an interview in 2015. ‘If this was going to produce liberation, we’d be free.’