The episode opens with Stewart-Williams reflecting on whether his new book could have been published six years ago — probably yes, but it would have landed far worse. Chris Williamson asks what makes sex differences so radioactive a topic, and Stewart-Williams traces the reaction back to science's historical misuse against women. He quotes Gustave Le Bon's remarkable 19th-century claim that intellectually accomplished women were roughly as rare as a two-headed gorilla, and notes how this legacy makes people instinctively recoil whenever evolved sex differences are discussed. Yet he insists the intuitive response has it backwards: modern science has systematically disproved those Victorian caricatures, not confirmed them. His central provocation — that science is the solution to early sexism, not a continuation of it — sets the tone for everything that follows.

Chris Williamson recalls the shared experience of reading Robert Wright's The Moral Animal and describes how it reframed his understanding of human nature in a single sitting. Stewart-Williams echoes the sentiment — the book shaped his entire career and gave him the feeling of sudden insight that childhood explanations of the moon's phases had. The conversation quickly turns to the unavoidable social charge surrounding the topic: even expressing fascination with sex differences invites accusations of motivated reasoning. Stewart-Williams disarms this with his four-word philosophy: let people be themselves. He is careful to insist that evolutionary origins carry no normative weight — something being natural does not make it good, permissible, or desirable. He also warns against using multivariate aggregation of small differences to exaggerate how distinct men and women actually are: the same technique could make New Zealanders and Australians look like different species.

Chris asks what sex actually is, and Stewart-Williams cuts straight to the scientific definition: sex is defined by gamete size. Organisms that produce small gametes are male; those that produce large gametes are female. This is not just a generalisation — it is a definitional truth that holds across almost every sexually reproducing species. The podcast then digs into why this binary is evolutionarily inevitable. Start with same-sized gametes (isogamy) and you get an unstable equilibrium: some gametes are selected to carry more nutrients (getting bigger), while others are selected to be tiny and numerous to seek out the larger ones. The medium-sized gametes — neither big enough to survive well nor small enough to be produced in huge numbers — go extinct. The result is always a barbell: eggs and sperm, females and males. A ChatGPT lookup provides comic illustration: global human sperm production is approximately 200 quadrillion, versus 70 million eggs.

The nature-versus-nurture question is the hardest challenge in sex-differences research, and Stewart-Williams tackles it methodically. He concedes upfront that socialisation has a real impact — sex differences do vary in size and detail across cultures. But he argues that six independent lines of evidence collectively make a compelling case for an innate contribution. First: many sex differences appear as early as toddlerhood, before meaningful socialisation could have taken effect — including the fact that boys end up in emergency rooms from risk-taking at higher rates essentially from the moment they can move. Second: many differences appear despite cultural pressure, not because of it — parents and teachers actually tell boys off for aggression more than girls, yet the aggression gap persists and widens at puberty. Third: they are remarkably persistent over time, with the people-versus-things career interest gap stable from the early 1900s to today. Fourth: hormonal correlates are strong — women with congenital adrenal hyperplasia (CAH), exposed to high prenatal testosterone, show more male-typical interests, career preferences, and rates of bisexuality. Fifth: most key differences are cross-culturally universal. Sixth and perhaps most compelling: the same patterns appear in other species subject to the same evolutionary selection pressures.

The nature-versus-nurture question is the hardest challenge in sex-differences research, and Stewart-Williams tackles it methodically. He concedes upfront that socialisation has a real impact — sex differences do vary in size and detail across cultures. But he argues that six independent lines of evidence collectively make a compelling case for an innate contribution. First: many sex differences appear as early as toddlerhood, before meaningful socialisation could have taken effect — including the fact that boys end up in emergency rooms from risk-taking at higher rates essentially from the moment they can move. Second: many differences appear despite cultural pressure, not because of it — parents and teachers actually tell boys off for aggression more than girls, yet the aggression gap persists and widens at puberty. Third: they are remarkably persistent over time, with the people-versus-things career interest gap stable from the early 1900s to today. Fourth: hormonal correlates are strong — women with congenital adrenal hyperplasia (CAH), exposed to high prenatal testosterone, show more male-typical interests, career preferences, and rates of bisexuality. Fifth: most key differences are cross-culturally universal. Sixth and perhaps most compelling: the same patterns appear in other species subject to the same evolutionary selection pressures.

The nature-versus-nurture question is the hardest challenge in sex-differences research, and Stewart-Williams tackles it methodically. He concedes upfront that socialisation has a real impact — sex differences do vary in size and detail across cultures. But he argues that six independent lines of evidence collectively make a compelling case for an innate contribution. First: many sex differences appear as early as toddlerhood, before meaningful socialisation could have taken effect — including the fact that boys end up in emergency rooms from risk-taking at higher rates essentially from the moment they can move. Second: many differences appear despite cultural pressure, not because of it — parents and teachers actually tell boys off for aggression more than girls, yet the aggression gap persists and widens at puberty. Third: they are remarkably persistent over time, with the people-versus-things career interest gap stable from the early 1900s to today. Fourth: hormonal correlates are strong — women with congenital adrenal hyperplasia (CAH), exposed to high prenatal testosterone, show more male-typical interests, career preferences, and rates of bisexuality. Fifth: most key differences are cross-culturally universal. Sixth and perhaps most compelling: the same patterns appear in other species subject to the same evolutionary selection pressures.

The nature-versus-nurture question is the hardest challenge in sex-differences research, and Stewart-Williams tackles it methodically. He concedes upfront that socialisation has a real impact — sex differences do vary in size and detail across cultures. But he argues that six independent lines of evidence collectively make a compelling case for an innate contribution. First: many sex differences appear as early as toddlerhood, before meaningful socialisation could have taken effect — including the fact that boys end up in emergency rooms from risk-taking at higher rates essentially from the moment they can move. Second: many differences appear despite cultural pressure, not because of it — parents and teachers actually tell boys off for aggression more than girls, yet the aggression gap persists and widens at puberty. Third: they are remarkably persistent over time, with the people-versus-things career interest gap stable from the early 1900s to today. Fourth: hormonal correlates are strong — women with congenital adrenal hyperplasia (CAH), exposed to high prenatal testosterone, show more male-typical interests, career preferences, and rates of bisexuality. Fifth: most key differences are cross-culturally universal. Sixth and perhaps most compelling: the same patterns appear in other species subject to the same evolutionary selection pressures.

Rather than dismissing sociocultural explanations, Stewart-Williams stress-tests them. Research in Western societies actually shows parents treat sons and daughters fairly similarly in key domains — equally encouraging independence and success. Behavioural genetics' second law (identical twins reared apart are often no more different as adults than those reared together) pulls the rug from claims about large parental effects. Then comes the centrepiece: the gender equality paradox ^{[1] — Steve Stewart-Williams "Social role theory says patriarchy inflates sex differences. The data say the opposite. In the most gender-equal, least patriarchal societi…" 35:00 Play} . Both social role theory and patriarchy theory predict that stricter gender norms and more patriarchal societies should amplify sex differences. The data consistently show the opposite — in more egalitarian, less patriarchal societies, differences in personality, career interests, and even physical traits like height actually tend to be larger. Stewart-Williams admits this surprised even him: he had expected patriarchy to push the sexes further apart. The sociocultural rebuttal — that sex-segregated societies skew self-report comparisons — is acknowledged but countered: the paradox also appears in objective cognitive and physical measures, not just personality surveys.

Rather than dismissing sociocultural explanations, Stewart-Williams stress-tests them. Research in Western societies actually shows parents treat sons and daughters fairly similarly in key domains — equally encouraging independence and success. Behavioural genetics' second law (identical twins reared apart are often no more different as adults than those reared together) pulls the rug from claims about large parental effects. Then comes the centrepiece: the gender equality paradox ^{[1] — Steve Stewart-Williams "Social role theory says patriarchy inflates sex differences. The data say the opposite. In the most gender-equal, least patriarchal societi…" 35:00 Play} . Both social role theory and patriarchy theory predict that stricter gender norms and more patriarchal societies should amplify sex differences. The data consistently show the opposite — in more egalitarian, less patriarchal societies, differences in personality, career interests, and even physical traits like height actually tend to be larger. Stewart-Williams admits this surprised even him: he had expected patriarchy to push the sexes further apart. The sociocultural rebuttal — that sex-segregated societies skew self-report comparisons — is acknowledged but countered: the paradox also appears in objective cognitive and physical measures, not just personality surveys.

Why are men more aggressive, more risk-taking, more interested in casual sex? Stewart-Williams traces all of these to a single upstream cause: variance in offspring number is greater in males. In many species, some males can sire vastly more offspring than any female can produce, while many males sire none. This creates intense selection pressure on males to compete for status, resources, and multiple mates. The famous 40/80 statistic — that only 40% of ancestral men reproduced versus 80% of ancestral women — comes up, and Stewart-Williams pushes back: he thinks the male reproductive skew in humans was actually lower than in most mammals, precisely because humans have unusually high biparental care. He explains why a 50-50 sex ratio is evolutionarily stable even when one male can theoretically service many females, using a clean parental-investment argument. Bateman's original principle and Trivers' extension to all forms of parental investment — gestation, birth, nursing, and beyond — are outlined clearly.

Why are men more aggressive, more risk-taking, more interested in casual sex? Stewart-Williams traces all of these to a single upstream cause: variance in offspring number is greater in males. In many species, some males can sire vastly more offspring than any female can produce, while many males sire none. This creates intense selection pressure on males to compete for status, resources, and multiple mates. The famous 40/80 statistic — that only 40% of ancestral men reproduced versus 80% of ancestral women — comes up, and Stewart-Williams pushes back: he thinks the male reproductive skew in humans was actually lower than in most mammals, precisely because humans have unusually high biparental care. He explains why a 50-50 sex ratio is evolutionarily stable even when one male can theoretically service many females, using a clean parental-investment argument. Bateman's original principle and Trivers' extension to all forms of parental investment — gestation, birth, nursing, and beyond — are outlined clearly.

The discussion drifts into one of the episode's most affecting tangents: research showing that parental grief tracks the reproductive value of the child who has died — rising through childhood, peaking a couple of years after puberty, then declining. Stewart-Williams notes this has been replicated since Robert Wright first discussed it in The Moral Animal. The case of Darwin — who lost ten children, with the death of his 12-year-old daughter Annie being the most psychologically devastating — illustrates the pattern. Nobody is consciously calculating reproductive value when they grieve; the proximate emotion of devastating loss is real and complete in itself. But the underlying evolutionary logic, operating invisibly, shapes the intensity of that grief anyway. This segues into a broader defence of evolutionary psychology's framing of emotion: the proximate feeling and the ultimate explanation are separate questions, and confusing them is one of the most common misreadings of the field.

Stewart-Williams explains the sex difference in sociosexuality — interest in no-strings-attached sex — with an effect size of around Cohen's d=1, making it one of the larger psychological sex differences. The evolutionary rationale traces back to reproductive variance: males that seek multiple partners can dramatically increase their offspring count; females cannot. He then makes a key correction to a common assumption: men being more interested in casual sex does not mean women are less interested in committed relationships. Both sexes are comparably invested in long-term pair bonds; women simply lack the additional layer of desire for casual variety. The natural experiment provided by gay men and lesbians ^{[1] — Steve Stewart-Williams "Gay men have more casual sex than straight men; lesbians have less than straight women. This isn't a coincidence — it's a natural experimen…" 1:11:35 Play} makes this vivid: gay men have more casual sex than straight men, while lesbians have less than straight women, showing exactly what each sex's baseline motivation looks like when the opposite-sex compromise is removed. The Ashley Madison data — 20 million male users versus 1,492 female users despite free membership for women — is cited as a real-world illustration. Men are also more turned on by visual stimuli, partly because youthfulness is a stronger fertility signal in women due to menopause.

Stewart-Williams explains the sex difference in sociosexuality — interest in no-strings-attached sex — with an effect size of around Cohen's d=1, making it one of the larger psychological sex differences. The evolutionary rationale traces back to reproductive variance: males that seek multiple partners can dramatically increase their offspring count; females cannot. He then makes a key correction to a common assumption: men being more interested in casual sex does not mean women are less interested in committed relationships. Both sexes are comparably invested in long-term pair bonds; women simply lack the additional layer of desire for casual variety. The natural experiment provided by gay men and lesbians ^{[1] — Steve Stewart-Williams "Gay men have more casual sex than straight men; lesbians have less than straight women. This isn't a coincidence — it's a natural experimen…" 1:11:35 Play} makes this vivid: gay men have more casual sex than straight men, while lesbians have less than straight women, showing exactly what each sex's baseline motivation looks like when the opposite-sex compromise is removed. The Ashley Madison data — 20 million male users versus 1,492 female users despite free membership for women — is cited as a real-world illustration. Men are also more turned on by visual stimuli, partly because youthfulness is a stronger fertility signal in women due to menopause.

Stewart-Williams explains the sex difference in sociosexuality — interest in no-strings-attached sex — with an effect size of around Cohen's d=1, making it one of the larger psychological sex differences. The evolutionary rationale traces back to reproductive variance: males that seek multiple partners can dramatically increase their offspring count; females cannot. He then makes a key correction to a common assumption: men being more interested in casual sex does not mean women are less interested in committed relationships. Both sexes are comparably invested in long-term pair bonds; women simply lack the additional layer of desire for casual variety. The natural experiment provided by gay men and lesbians ^{[1] — Steve Stewart-Williams "Gay men have more casual sex than straight men; lesbians have less than straight women. This isn't a coincidence — it's a natural experimen…" 1:11:35 Play} makes this vivid: gay men have more casual sex than straight men, while lesbians have less than straight women, showing exactly what each sex's baseline motivation looks like when the opposite-sex compromise is removed. The Ashley Madison data — 20 million male users versus 1,492 female users despite free membership for women — is cited as a real-world illustration. Men are also more turned on by visual stimuli, partly because youthfulness is a stronger fertility signal in women due to menopause.

The conversation turns to the cultural puzzle of pornography versus romance novels. Men consume vastly more porn; women consume vastly more romance fiction and 'romantasy.' A common assumption is that this maps onto a male preference for casual sex and a female preference for relationships. Stewart-Williams challenges this: men and women are approximately equally interested in long-term committed relationships. The sex difference is additive, not substitutive — men have the same romantic drive plus an extra layer of interest in casual variety. In some respects, research suggests men are actually the more romantic sex: they fall in love faster, say 'I love you' sooner, and suffer more intensely after breakups. Why women still dominate romance novel consumption despite this remains somewhat unexplained. The mental-fantasy data — men cycle through four to six partners during a single fantasy while women tend to stick to one — is consistent with the broader pattern.

Despite all the emphasis on sex differences, Stewart-Williams is quick to note how similar male and female long-term mate preferences actually are: both sexes prioritise kindness, intelligence, mutual attraction, emotional stability, and good looks. The differences are in the weighting. Men place somewhat more value on physical appearance because youthfulness is a stronger fertility proxy in women (due to menopause). Women place somewhat more value on resources and status, either because these predict investment in children or because they signal good genes — or both. Crucially, in short-term mating contexts, this difference in emphasis on physical attractiveness nearly disappears: when commitment is off the table, genes are all that's left to assess, so women's preferences for physical markers of genetic quality sharpen dramatically. The evolutionary logic of status signals — expensive watches, fast cars in Miami nightclubs — is framed as the human equivalent of the peacock's tail, culturally variable in form but universally present in function.

Chris introduces the sperm-donor thought experiment: strip away seduction and you isolate exactly what traits women want their children to inherit. Stewart-Williams confirms the same preferences emerge, validating that mate-choice criteria are not just artifacts of attraction. The Clark-Hatfield study ^{[1] — Steve Stewart-Williams "In the Clark-Hatfield study, a good-looking stranger approached random campus students offering a date, a visit to their room, or immediate…" 2:04:08 Play} then provides the starkest possible empirical illustration: good-looking strangers approached random university students with offers ranging from a date to immediate sex. For the sex offer, 75% of men agreed; 0% of women did. Men who declined were apologetic and asked for a rain check. Women who were approached reacted with disgust and demanded an explanation. The divergent manner of refusal — not just the rate — is itself data about baseline motivations. The sexual overperception bias is introduced: men systematically overestimate women's sexual interest because the cost of a missed opportunity historically exceeded the cost of an awkward rejection. Women show the mirror-image bias, underestimating men's interest.

The conversation turns to one of the most discussed and misunderstood sex differences: women's attraction to men with the capacity for violence. Stewart-Williams frames it carefully — aggression per se is not attractive; protectiveness is, and muscularity and height are proxy signals for it. Andrew Thomas's theory is introduced: women prefer men who can turn violence on and off, not men with globally elevated aggression. This carries a real trade-off: the same traits that make a man a credible protector also make him a credible threat. Research is cited (though the original source was elusive) suggesting women would lose more attraction if their partner failed to protect them during a physical confrontation than if he cheated on them — and that the key variable is willingness to protect, not physical capability alone. The height preference is linked to the same cluster: above-average height signals protective capacity regardless of the absolute size of the woman being protected.

Stewart-Williams outlines how the aggression sex difference is not monolithic but scales with severity. Verbal aggression shows a modest gap (effect size ~0.5). Physical aggression shows a larger one. Homicide shows an enormous one: over 90% of killings are perpetrated by men in every nation where data exists. The chimpanzee comparison is striking — male chimps commit 92% of chimpicides and make up 73% of victims, virtually identical to human ratios of 95% and 70–80%. Both patterns trace to the same evolutionary root: male reproductive variance creates intense selection for within-sex competition. Sexual violence is then examined as the interaction of two sex differences — men's greater interest in casual sex and their greater willingness to use violence — and Stewart-Williams argues that the depth of women's evolutionary distress at sexual coercion reflects the fact that female mate choice is one of the most evolutionarily fundamental and protected drives across the animal kingdom. Analysis is not justification: the evolutionary account explains the pattern without excusing a single instance of it.

Stewart-Williams outlines how the aggression sex difference is not monolithic but scales with severity. Verbal aggression shows a modest gap (effect size ~0.5). Physical aggression shows a larger one. Homicide shows an enormous one: over 90% of killings are perpetrated by men in every nation where data exists. The chimpanzee comparison is striking — male chimps commit 92% of chimpicides and make up 73% of victims, virtually identical to human ratios of 95% and 70–80%. Both patterns trace to the same evolutionary root: male reproductive variance creates intense selection for within-sex competition. Sexual violence is then examined as the interaction of two sex differences — men's greater interest in casual sex and their greater willingness to use violence — and Stewart-Williams argues that the depth of women's evolutionary distress at sexual coercion reflects the fact that female mate choice is one of the most evolutionarily fundamental and protected drives across the animal kingdom. Analysis is not justification: the evolutionary account explains the pattern without excusing a single instance of it.

The parenting sex difference is among the most politically sensitive findings in the field. Stewart-Williams presents it carefully: in every culture where good data exists, women do more direct parenting than men, even though human males do vastly more than most male mammals. Average differences in parental inclinations — not just social coercion by men — seem to be part of the explanation. The kibbutz experiment ^{[1] — Steve Stewart-Williams "Israeli kibbutzim tried to replace biological parenting with communal child-rearing to eliminate traditional gender roles. It worked briefl…" 1:55:35 Play} provides a natural test: Israeli communes that tried to replace biological parenting with communal child-rearing found that parents hated it. Crucially, it was the mothers — more than the fathers — who agitated against the arrangement and eventually broke it down. This is a classic example of a sex difference emerging despite culture, not because of it. Stewart-Williams then introduces his 'soft bigotry of male expectations' critique (coined by Williamson): the implicit assumption that whatever men do is the norm means that saying women are more naturally parental is treated as an insult — which only makes sense if parenting is devalued, which is itself deeply sexist.

The parenting sex difference is among the most politically sensitive findings in the field. Stewart-Williams presents it carefully: in every culture where good data exists, women do more direct parenting than men, even though human males do vastly more than most male mammals. Average differences in parental inclinations — not just social coercion by men — seem to be part of the explanation. The kibbutz experiment ^{[1] — Steve Stewart-Williams "Israeli kibbutzim tried to replace biological parenting with communal child-rearing to eliminate traditional gender roles. It worked briefl…" 1:55:35 Play} provides a natural test: Israeli communes that tried to replace biological parenting with communal child-rearing found that parents hated it. Crucially, it was the mothers — more than the fathers — who agitated against the arrangement and eventually broke it down. This is a classic example of a sex difference emerging despite culture, not because of it. Stewart-Williams then introduces his 'soft bigotry of male expectations' critique (coined by Williamson): the implicit assumption that whatever men do is the norm means that saying women are more naturally parental is treated as an insult — which only makes sense if parenting is devalued, which is itself deeply sexist.

Both sexes are prone to jealousy, but the triggers differ systematically. For men, sexual infidelity is typically more distressing than emotional infidelity because it introduces paternity uncertainty — the only species-wide reproductive threat unique to males. For women, emotional infidelity tends to be more distressing because it signals probable desertion: a partner who falls in love with someone else is likely to leave, which was historically catastrophic for a woman with dependent children. This asymmetry generates different mate-guarding behaviour: men are more focused on monitoring sexual access, women on monitoring emotional commitment. A 23andMe anecdote about a paternal affair discovered three decades later prompts a discussion of how jealousy evolved as a gut reaction that fires regardless of whether the evolutionary circumstances still apply — another illustration of proximate versus ultimate causation.

Moving to personality, Stewart-Williams focuses on the two most consistent sex differences in the Big Five: neuroticism (women higher, ~0.2–0.5 SD) and agreeableness (women higher, ~0.2–0.5 SD). Neuroticism is explained as the flip side of male risk-taking — anxiety is self-protective, and women evolved more of it because the cost-benefit calculus of risk is different when your ceiling offspring number is lower. Agreeableness maps onto reduced within-sex competition and stronger selection for cooperative, compassionate social bonding. Smaller differences in openness, conscientiousness, and extraversion are noted. The episode's most empirically striking finding in this section is the people-versus-things career interest gap ^{[1] — Steve Stewart-Williams "People vs things difference found in 80/80 nations: The sex difference in people-versus-things career interests was found in 53 out of 53 n…" 2:06:40 Play} : an effect size of around one standard deviation or more, first documented in 1911, and found in 53/53 nations in one study and 80/80 in another with half a million participants. Despite decades of deliberate social pressure to close it, the gap has not budged. Its persistence through the gender equality paradox — growing larger in more egalitarian societies — is one of the strongest arguments for an innate contribution.

Stewart-Williams acknowledges cognitive abilities as the most controversial terrain in the book and navigates it with notable care. The headline finding: no meaningful sex difference in average general intelligence (IQ). Some studies show tiny male advantages, but Stewart-Williams attributes this to sampling bias — low-IQ males are more likely to 'fall through the cracks' and miss inclusion in studies, slightly inflating the female average. The real cognitive sex difference is in variance: males show slightly greater spread at both extremes, meaning more male geniuses and more males with intellectual disabilities. This is a relatively small effect, and he is quick to note that where specific ability differences exist, they are equally likely to favour women (verbal ability) as men (spatial ability). An intriguing wrinkle: among highly mathematically gifted individuals, women are more likely than men to also be verbally gifted — a 'double threat' advantage. Cognitive sex differences are smaller than personality differences, which are themselves smaller than interest differences.

Stewart-Williams surveys the major physical health sex differences: men are more prone to cardiovascular disease, most cancers, and early death; women are more prone to immune disorders and pain conditions. The male mortality disadvantage is particularly stark — men die younger than women in the vast majority of cultures, including most where women face high maternal mortality. The mechanism becomes clear when you consider the Korean Joseon Dynasty eunuch data ^{[1] — Chris Williamson "Eunuchs lived longer than intact men: Korean Joseon Dynasty eunuchs lived significantly longer than intact males of identical social standi…" 2:17:30 Play} : eunuchs castrated before puberty lived significantly longer than intact males of identical social standing, directly implicating testosterone. Stewart-Williams points out we technically already have a known intervention to close the lifespan gap — it just comes with obvious drawbacks. Randy Nesse's evolutionary medicine calculation ^{[2] — Chris Williamson "Curing male mortality gap > curing cancer: Evolutionary medicine researcher Randy Nesse calculated that if male mortality rates were reduce…" 2:18:38 Play} lands as the most striking statistic in this section: if male mortality rates were reduced to female levels, more years of life would be saved than if cancer were entirely cured. The 88%/90% symmetry of Darwin Awards and Carnegie Hero Awards closes the section: male risk-taking cuts in both catastrophic and heroic directions with almost identical frequency.

The final substantive chapter is Stewart-Williams's most pointed policy argument. He takes direct aim at the asymmetry in public discourse: enormous attention is paid to the dangers of exaggerating sex differences, virtually none to the dangers of denying them. But denial has concrete costs. Women's cardiac symptoms — more likely to involve shortness of breath than the classic male 'shooting pain down the arm' — are routinely missed because doctors trained on the male presentation fail to look for them. Autism is underdiagnosed in girls because the female presentation involves fewer repetitive behaviours. Male victims of intimate partner violence are systematically undercounted because the assumption that abuse only flows male-to-female prevents anyone from looking in the other direction. Exaggeration carries symmetric costs: men's depression goes unnoticed when the disorder is framed as a female problem, occupational gender gaps are misattributed entirely to discrimination when preferences also play a role, and coercive interventions designed to close gaps that are partly preference-driven generate resentment without fixing the underlying issue. Stewart-Williams closes by noting a fascinating irony: the people most likely to minimise sex differences in general are often the same people who maximise and moralise them when it comes to violence and harassment — a selective application that reveals motivated reasoning on both sides.

The final substantive chapter is Stewart-Williams's most pointed policy argument. He takes direct aim at the asymmetry in public discourse: enormous attention is paid to the dangers of exaggerating sex differences, virtually none to the dangers of denying them. But denial has concrete costs. Women's cardiac symptoms — more likely to involve shortness of breath than the classic male 'shooting pain down the arm' — are routinely missed because doctors trained on the male presentation fail to look for them. Autism is underdiagnosed in girls because the female presentation involves fewer repetitive behaviours. Male victims of intimate partner violence are systematically undercounted because the assumption that abuse only flows male-to-female prevents anyone from looking in the other direction. Exaggeration carries symmetric costs: men's depression goes unnoticed when the disorder is framed as a female problem, occupational gender gaps are misattributed entirely to discrimination when preferences also play a role, and coercive interventions designed to close gaps that are partly preference-driven generate resentment without fixing the underlying issue. Stewart-Williams closes by noting a fascinating irony: the people most likely to minimise sex differences in general are often the same people who maximise and moralise them when it comes to violence and harassment — a selective application that reveals motivated reasoning on both sides.

The final substantive chapter is Stewart-Williams's most pointed policy argument. He takes direct aim at the asymmetry in public discourse: enormous attention is paid to the dangers of exaggerating sex differences, virtually none to the dangers of denying them. But denial has concrete costs. Women's cardiac symptoms — more likely to involve shortness of breath than the classic male 'shooting pain down the arm' — are routinely missed because doctors trained on the male presentation fail to look for them. Autism is underdiagnosed in girls because the female presentation involves fewer repetitive behaviours. Male victims of intimate partner violence are systematically undercounted because the assumption that abuse only flows male-to-female prevents anyone from looking in the other direction. Exaggeration carries symmetric costs: men's depression goes unnoticed when the disorder is framed as a female problem, occupational gender gaps are misattributed entirely to discrimination when preferences also play a role, and coercive interventions designed to close gaps that are partly preference-driven generate resentment without fixing the underlying issue. Stewart-Williams closes by noting a fascinating irony: the people most likely to minimise sex differences in general are often the same people who maximise and moralise them when it comes to violence and harassment — a selective application that reveals motivated reasoning on both sides.

The final substantive chapter is Stewart-Williams's most pointed policy argument. He takes direct aim at the asymmetry in public discourse: enormous attention is paid to the dangers of exaggerating sex differences, virtually none to the dangers of denying them. But denial has concrete costs. Women's cardiac symptoms — more likely to involve shortness of breath than the classic male 'shooting pain down the arm' — are routinely missed because doctors trained on the male presentation fail to look for them. Autism is underdiagnosed in girls because the female presentation involves fewer repetitive behaviours. Male victims of intimate partner violence are systematically undercounted because the assumption that abuse only flows male-to-female prevents anyone from looking in the other direction. Exaggeration carries symmetric costs: men's depression goes unnoticed when the disorder is framed as a female problem, occupational gender gaps are misattributed entirely to discrimination when preferences also play a role, and coercive interventions designed to close gaps that are partly preference-driven generate resentment without fixing the underlying issue. Stewart-Williams closes by noting a fascinating irony: the people most likely to minimise sex differences in general are often the same people who maximise and moralise them when it comes to violence and harassment — a selective application that reveals motivated reasoning on both sides.