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What sex-difference science misses about the messy reality of sex | Psyche

Photo by Martin Parr/Magnum

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What sex-difference science misses about the messy reality of sex

Photo by Martin Parr/Magnum

by Jeffrey W Lockhart + BIO

Sex sells. Not in the erotic sense (although that sells, too), but in the ‘men are from Mars and women are from Venus’ sense. Enormous scientific and publishing resources go to studying differences between male and female; findings of sex differences get outsized media and public attention. And while sex is an important part of our biology and society, the search for biological differences can lead us astray, too.

Listen to one of the advocates for sex-difference research and you will likely hear a familiar narrative. Women were excluded from clinical trials for a long time, meaning we do not know how medications will affect them, how symptoms might manifest, or what might interact with birth control, because we never tested on women. Therefore, it is important that we study not just women, but differences between women and men.

The search for sex differences has generated a breathless flurry of new results – more than 1,100 research papers per year by my last count, along with whole new academic journals and professional societies dedicated to sex differences. Based on the same logic, the US National Institutes of Health (NIH) added to the frenzy in 2016 by making the study of ‘sex as a biological variable’ a stipulation of their research funding, which totals more than $41 billion and reaches more than 300,000 researchers annually.

But there is more to the story. In 1986, the United States reversed its nine-year-long policy recommendation to exclude women from clinical trials. After 1993, women’s inclusion in them was required by law. Yet the subsequent three decades of clinical trials with both men and women did not produce the torrent of sex-difference findings that advocates had expected. To date, only one medication is recommended at different dosages for men and women by the US Food and Drug Administration (zolpidem, the active ingredient in the sleep aid Ambien). The evidence for a meaningful sex difference in how men and women process the drug was weak enough at the time that European regulators did not recommend different doses for men and women, and since then additional evidence has cast more doubt on the need for sex-specific dosing. Doubts aside, one clinically relevant finding in three decades of clinical trials is not a good track record for theories of omnipresent and often omnipotent sex differences embodied in slogans such as ‘every cell has a sex’.

The 2016 NIH policy required expanding the search for sex differences from clinical trials into preclinical and basic research, where the search for sex differences was already taking place but was not required. Unlike clinical trials, preclinical and basic research has far broader implications than medical treatment, as scientists in this area tell us. The Cambridge scholar Simon Baron-Cohen says he does sex-difference research and public engagement because he would like to give men ‘a resurgence of pride’. Baron-Cohen argues there is an ‘essential difference’ between male and female brains, where male brains are excellent at jobs like engineer, banker and lawyer, and female brains as better at jobs like primary school teacher, therapist and personnel staff. Others, such as the neuroscientist Melissa Hines, are sceptical of arguments that men and women have fundamentally different abilities, arguing instead that they have innately different preferences. In other words, these scholars do not argue that women are incapable of doing what men do, but rather that they are biologically programmed to want other things.

Reading essentialist descriptions of sex differences can make people endorse gender stereotypes more, even if the science is about plants

As scientists, we draw our ideas from the cultural and physical worlds around us, just like everyone else. For hundreds of years, those cultural worlds have led scientists to try to prove that women are fundamentally different from and/or inferior to men. The broad cultural appetite for those claims makes studying sex responsibly difficult even today. While thousands of new sex differences are ‘discovered’ and published each year, only a vanishingly small number of them stand up to replication. ‘Hype and hyperbole’ distort both the public’s and scientists’ understanding of sex differences to make them seem more common and larger than they really are. As comedy Twitter accounts such as @justsaysinmice remind us, preclinical research showing sex differences in animals often does not translate to humans, because our biological and social systems are different. Similarly, searching for sex in ‘every cell’ can become nonsensical when cells used in many studies have lost their X and Y chromosomes.

In trying to understand these failures and counteract the influence of sexist cultural assumptions on research, scientists have ended up debunking essentialist theories of sex in every field, including endocrinology (the study of hormones such as testosterone); neuroscience (brain research); genetics; psychology of cognitive abilities, personality and behaviour; pharmacology; cellular research; and reproductive health.

Despite their often-tenuous nature, new ‘findings’ of essentialist sex differences are being published and reported in the media faster than ever, and they can have harmful effects on both society and scientists themselves. Reading essentialist scientific descriptions of sex differences can make people endorse gender stereotypes more, even if the science is about sex in plants. Similarly, exposure to race-based scientific descriptions of sickle cell anaemia increases students’ beliefs in racial intelligence differences, decreases their willingness to socialise across racial lines, and decreases their support for policies reducing racial inequality. Science with race and sex essentialist claims is also widely taken up by Right-wing extremists as justification for their views and actions.

This works because of what psychologists call ‘neurogenetic essentialism’. People hear that one difference between groups is biological, and wrongly assume all differences are biological. Hearing about even an unrelated or spurious biological difference between groups such as ‘male’ and ‘female’ can strengthen people’s belief in four key aspects of neurogenetic essentialism: first, the uniformity of groups, eg ‘all women are the same’. Second, the discreteness of groups, eg ‘men and women do not overlap’. Third, that there is an underlying essence of groups, eg ‘men have different brains or genetics’. And fourth, that those essences cause people’s appearances and behaviours.

Larry Summers made this mistake in 2005 when, as president of Harvard, he asserted that ‘intrinsic aptitude’ was the most important reason there are more men than women in STEM (science, technology, engineering and mathematics). Summers had not seen any evidence of men’s greater STEM ability, or even any research about sex/gender. Instead, he pointed to the field of behaviour genetics broadly as evidence that ‘things that people thought were due to socialisation weren’t, and were in fact due to more intrinsic human nature, and that set of discoveries, it seemed to me, ought to influence the way one thought about other areas’ – areas such as women’s STEM ability, about which Summers had no specific evidence.

These (baseless) beliefs have consequences. They can create a hostile work environment, leading some to quit academia. Further, transcripts from hiring committee meetings show that gendered assumptions can lead committees to deny even highly qualified women jobs. When university presidents such as Summers believe culture and discrimination are not major problems, it is a safe bet they will invest less in improving culture and reducing discrimination. Research shows that women and African Americans earn fewer bachelor’s degrees and fewer PhDs in fields where more practitioners believe ability is innate. My own work shows that women historically earn fewer PhDs in biology and health subfields when those fields publish more claims of essential sex differences.

Social scientists can tell us as much or more than biologists about the direct consequences these aspects of sex-related embodiment have for our lives

Those of us trying to relate sex science to everyday lives then have two major obstacles. First, sex is really complicated biologically, meaning that simplistic male-versus-female sex-difference research rarely holds up, or adequately describes how our bodies work. The solution is not for scientists to ignore sex, but to study it in all of its complexity, to understand that biological sex means different things in different contexts, that, instead of categorical distinctions, sex is often better understood as a set of messy, contradictory, overlapping phenomena engaged in feedback cycles with other biological and social processes. That is to say, there is no straight line between even simple biological things such as gametes (sperm and eggs) and body-fat distribution, let alone more complex and socially contingent phenomena such as housework, engineering or violence.

The second obstacle is that what science can tell us about sex is often far removed from what we actually care about. Biologically, one could say the core of human sex is anisogamy: one large gamete (an egg) joins with one smaller one (a sperm) to generate offspring. While it is more complicated than that, and other species do sexual reproduction differently, this is fairly uncontroversial. But anisogamy is not a very useful definition of sex unless we are trying to make a baby. When we talk about equal opportunities in education and the workplace, sexual harassment and discrimination, the division of household labour, or sport and bathroom access, we are not talking about gametes. In these conversations, we do not worry whether the one-in-20 men who are infertile should count as men or if the one-in-three women who undergo a hysterectomy are still women. Sperm and eggs are not the point, and extrapolating all of the social differences we care about for men and women from the gametes they do (or do not) produce is precisely the error of neurogenetic essentialism.

Our political, social and even most of the biological interest in sex lies elsewhere, in myriad sex-related things including hormone levels, muscle and fat distribution, body hair, voice pitch, physical and mental abilities, personality traits and preferences, and so on. Unlike gametes or chromosomes, these are things we see, hear and feel, and none of them are remotely binary or fixed. When it comes to these topics, social scientists can tell us as much or more than biologists about the direct consequences these aspects of sex-related embodiment have for our personal, professional and social lives.

No doubt more studies finding major sex differences between men and women will continue to be published, but scientists and the public should be wary of these overhyped and often later-debunked claims. It is time to get past ‘men are from Mars and women are from Venus’. We are all on Earth, where sex is messy, dynamic and socially situated.

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17 August 2022