Jul 6, 2026 · 2h 33m
Evolutionary psychologist warns denying innate sex differences harms societal progress
The Uncomfortable Science Of Sex Differences - Steve Stewart-Williams - #1120
Understanding the evolutionary roots of human behavior is essential for creating effective social policies that respect individual choices without denying biological reality.
- 1Biological sex is fundamentally defined by gamete size, creating distinct evolutionary pressures that shape male and female behavior.
- 2The gender equality paradox reveals that progressive social policies often widen rather than narrow sex differences in career choices.
- 3Parental investment theory explains robust differences in mating strategies, risk-taking, and physical aggression across species.
Don't miss
Steve Stewart-Williams explains the gender equality paradox and why progressive societies see wider gaps in career choices.
The brief
Evolutionary psychologist Steve Stewart-Williams joins Chris Williamson to examine the biological and psychological differences between men and women, arguing that denying innate sex differences poses a severe threat to both science and individual choice.
A central focus is the gender equality paradox, where more egalitarian societies actually exhibit larger, rather than smaller, sex differences in personality and career choices as individuals gain the freedom to pursue their innate preferences.
The discussion grounds these behavioral patterns in parental investment theory, showing how the biological asymmetry of large eggs versus small sperm drives distinct evolutionary strategies in mating, risk-taking, and aggression across species.
They explore how these evolutionary forces manifest in modern life, from distinct triggers for sexual and emotional jealousy to cognitive variance and the extreme representation of men at both the positive and negative ends of risk outcomes.
What was said on this episode
59 statements · 15 positive · 20 negative · 8 mixed · 16 neutral
Sex-differences science has disproved claims of women’s intellectual inferiority.
“I think that really the science of sex differences has disproved those kind of ideas.”
Listen at 1:30
People should be allowed to follow or reject traditional gender roles.
“let people be themselves”
Listen at 4:44
Evolutionary origins do not determine whether traits are morally good or bad.
“The fact that something has evolutionary origin doesn't necessarily mean that it's good. It doesn't necessarily mean it's bad either.”
Listen at 4:56
Most psychological sex differences are modest, with substantial within-sex variation and overlap.
“most of the gaps are not huge, most of the psychological sex differences are not huge, that there's a huge amount of variation within both sexes, tons of overlap between the sexes”
Listen at 5:56
Biological sex is defined by the size of gametes produced.
“sex is defined in terms of gamete size”
Listen at 8:09
Selection drives initially equal gametes toward differentiated smaller and larger gametes.
“when you have same size gametes, this selection for any trait that will increase the chances of being one of the gamete, of producing gametes that are going to produce offspring that survive”
Listen at 10:05
Sex is binary in species producing sperm or eggs, despite substantial within-sex variation.
“there is a sex binary”
Listen at 11:47
Sex differences in aggression and risk-taking appear very early in childhood.
“The aggression sex difference and the risk taking sex difference, both of those appear basically as soon as kids are mature enough that they can move around the place and are capable of risk taking, capable of aggressing, you get that sex difference like immediately.”
Listen at 14:55
Career-interest sex differences have persisted across the twentieth century.
“sex differences in career preferences as well, or career related interests. They were evident from the early 1900s when people first started measuring them and then they just stayed the same.”
Listen at 18:12
Shared childhood environments often add little adult personality similarity among identical twins.
“By adulthood though, they're often not much more similar at all, and in some cases no more similar than they would be if they had grown up apart.”
Listen at 21:13
Some sex differences are larger in more gender-equal societies.
“in more gender equal societies, societies that are less strict in terms of their gender roles and societies that are less patriarchal, you actually find larger sex differences, often rather than smaller ones.”
Listen at 22:49
Most men are primarily attracted to women, while most women are primarily attracted to men.
“The vast majority of men are primarily attracted to women. The vast majority of women primarily attracted to men.”
Listen at 28:29
Men score higher than women on average in sociosexuality.
“men on average score higher. However you measure that trait. They score higher than women on that trait.”
Listen at 29:31
Higher prenatal testosterone is associated with later aggression, risk-taking, and reduced parental inclination.
“higher levels of testosterone in the womb, for instance, are associated with high levels of aggression, later, high levels of risk taking, lower levels of parental inclinations and so on.”
Listen at 31:31
Prenatal testosterone exposure in females is associated with more male-typical traits.
“women who, when they're in the womb are exposed to very, very high levels of prenatal testosterone due to having a condition called congenital adrenal hyperplasia, or cah. They as girls and then as women, they exhibit a lot of male typical traits.”
Listen at 31:54
Many key sex differences appear across all or most cultures.
“most of the key sex differences that we've been discussing so far, they are found either in every culture or in the vast majority.”
Listen at 32:47
Greater female parental investment lowers females’ maximum potential number of offspring.
“the females, on the other hand, they invest a lot in each offspring. That lowers the ceiling for the number of offspring they can produce.”
Listen at 40:35
Humans resemble birds more than mammals in pair bonding and biparental care.
“in our primary reproductive behavior, humans are more like the average bird than like the average mammal.”
Listen at 56:07
Human males have greater reproductive variance than females, but less than most mammals.
“Men do have and have always had greater reproductive variance than women, but it's relatively low compared to most mammals.”
Listen at 57:33
Men place more weight on youthfulness because female fertility declines through menopause.
“men place a greater weight on those traits because of menopause, basically.”
Listen at 1:03:42
Women place more weight than men on resources and status in long-term mates.
“Women, on the other hand, tend to put more weight on resources and status and a long term mate than men do.”
Listen at 1:15:28
In the Clark-Hatfield study, more men than women accepted a direct offer of sex.
“75% of men said yes to that offer. So an even higher rate of men, whereas exactly 0% of women and said yes to the kind offer.”
Listen at 1:24:47
Men perpetrate more than 90% of homicides across available datasets.
“90 plus percent of homicides are perpetrated by men.”
Listen at 1:30:33
Men perpetrate sexual violence more often than women.
“Men are much more likely to do it.”
Listen at 1:45:19
Women provide more direct parenting and invest more in children across cultures.
“in every culture, again, where we have good data, women do more of the direct parenting than men do and they invest more in the young”
Listen at 1:52:25
In Israeli kibbutzim, mothers resisted communal childrearing more strongly than fathers.
“although both parents hated it, most of the mothers particularly hated it. And a lot of the agitation came from the mothers more than the fathers.”
Listen at 1:55:56
Higher local income inequality is associated with greater female self-sexualization and stratification.
“in areas with higher income inequality, women did more self sexualization and more stratification”
Listen at 2:11:06
Men's preferred female body size varies with economic conditions.
“men are more attracted to bigger women in times of poor economy and more attracted to skinnier women in times of bad. In times of good economy.”
Listen at 2:11:44
Men and women do not differ in average IQ or general cognitive ability.
“there are no sex differences in the cognitive ability that matters most to most people, which is IQ or general cognitive ability”
Listen at 2:13:48
Unbalanced IQ tests still produce similar male and female averages in representative samples.
“even when they haven't, they give basically the same averages with representative samples of people”
Listen at 2:14:31
Cognitive ability varies slightly more among men than women.
“The variance is slightly greater in men than in women.”
Listen at 2:15:04
Highly mathematically gifted women are more likely than men to also have high verbal ability.
“among the minority people who are really, really gifted at maths, the women are more likely than the men to also be gifted verbally”
Listen at 2:15:41
Men tend to perform better spatially, while women tend to perform better verbally.
“Spatial abilities, that's an example. Verbal abilities, though, women tend to be somewhat better.”
Listen at 2:16:05
Specific cognitive sex differences are likely partly innate and partly shaped by culture.
“Very likely, I think, to be partly innate.”
Listen at 2:16:40
Men are more prone than women to cardiovascular disease.
“men are more prone to cardiovascular disease”
Listen at 2:17:05
Women are more prone than men to immune-system and pain disorders.
“Women are more prone to immune system disorders, they're more prone as well to pain disorders.”
Listen at 2:17:18
Men are more prone to most cancers except sex-specific reproductive cancers.
“Men are more prone to most forms of cancer, other than sort of reproductive cancers that only strike one sex or the other.”
Listen at 2:17:26
Prepubertal castration could eliminate the average male-female lifespan difference.
“castration before you Hit puberty”
Listen at 2:18:21
Testosterone increases male size, strength, and aggression while shortening male lifespan.
“it would work is, it's interesting. Does show that it's testosterone that is making us bigger, stronger, more aggressive, but also shortening our lifespan as well.”
Listen at 2:18:30
Reducing male mortality to female rates would save more life-years than curing cancer.
“If male mortality were at female rates, we would save more years of life than if we cured cancer.”
Listen at 2:18:50
Men constitute 88% of Darwin Award deaths and 90% of Carnegie Hero recipients.
“88% of people who die through stupid self inflicted ways are guys. And 90% of people who risked one's life to save a stranger are also guys.”
Listen at 2:19:22
Greater risk-taking increases both men's chances of business success and failure.
“They're more likely to go in both directions. So they're more likely to succeed because they take bigger risks, More likely to fail because they take bigger risks.”
Listen at 2:19:59
People should receive complete information about the benefits and costs of risky choices.
“Tell men and women all the facts. This approach to life, this risky approach cuts both ways.”
Listen at 2:20:24
After removing bias and barriers, society should respect individuals' career and life choices.
“respect people's choices about their own lives and how they want to live them and what careers they want to do.”
Listen at 2:20:49
Attributing occupational gender gaps entirely to discrimination can create unnecessary resentment.
“if we say any kind of gaps that you see are products of discrimination, first of all, it's going to create unnecessary resentment”
Listen at 2:22:01
Interventions targeting discrimination may fail when preferences primarily cause occupational gender gaps.
“Those interventions are probably not going to work because they're targeting things that are not the causes, the primary causes of the gaps in the first place.”
Listen at 2:22:18
Women are more prone than men to depression and anxiety.
“women are more prone to depression and anxiety”
Listen at 2:23:42
Men are slightly more prone than women to schizophrenia.
“Men are slightly more prone to schizophrenia.”
Listen at 2:23:58
Men are much more prone than women to antisocial personality disorder and psychopathy.
“Men are much more prone to like antisocial personality disorder, sociopathy, psychopathy”
Listen at 2:24:01
Bipolar disorder occurs at approximately equal frequencies in men and women across cultures.
“you don't find a sex difference is bipolar disorder. That is, I'd say in the book that that's the least sexist disorder on record because it's basically this same across cultures. It's about the same frequency of both sexes.”
Listen at 2:24:12
Sex differences in depression and anxiety may result from sex differences in neuroticism.
“with the depression and anxiety, I think that's just a side effect of the neuroticism sex difference”
Listen at 2:24:31
Clinical depression and anxiety are not adaptive traits, despite adaptive average-level differences.
“I don't accept adaptive explanations for clinical depression or clinical levels of anxiety depression disorders.”
Listen at 2:25:09
Autism and ADHD are more common among boys than girls.
“autism is more common among boys and girls. ADHD is more common among boys and girls as well.”
Listen at 2:25:41
Ignoring sex differences may cause clinicians to overlook women’s heart-attack symptoms.
“if you don't focus on sex differences, you might be more likely to overlook the symptoms of heart attacks in women”
Listen at 2:28:19
Autism is likely underdiagnosed in girls because its presentation differs by sex.
“there is a strong case that it's under diagnosed in girls”
Listen at 2:28:37
Assuming partner abuse is exclusively male-to-female underestimates female-to-male abuse.
“If we assume that all intimate partner abuse only goes in one direction, like male to female, then we're going to to underestimate the center, which sometimes goes in the, in the other direction.”
Listen at 2:29:06
Men predominate in severe aggression even in Western societies.
“when it comes to severe aggression, though even in the west, men do predominate”
Listen at 2:29:45
Exaggerating sex differences in cardiovascular disease can cause women’s cases to be overlooked.
“If you exaggerate the frequency of cardiovascular health problems, you will say, well, you find them in men, not women.”
Listen at 2:30:47
Men account for approximately one-third of depression cases.
“And a significant minority of people who suffer depression are men. About a third of cases are guys.”
Listen at 2:31:20
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