Speaker
Steve Stewart-Williams
Appearances over time
1 episodes
Episodes
1
Podcasts
Quotes & moments
In more gender-equal, less patriarchal societies, sex differences in personality, career preferences, and some cognitive abilities tend to be larger, not smaller — the opposite of what social role theory predicts.
The sex difference in verbal aggression has an effect size of about 0.5, but for homicide the gap is enormous — men perpetrate 90%+ of killings in every nation where data exists.
The commonly cited figure that only 40% of ancestral men reproduced versus 80% of women is likely an overestimate of male reproductive skew, according to Stewart-Williams, because humans have unusually high levels of biparental care.
Men score about one standard deviation higher than women on sociosexuality (interest in casual, no-strings-attached sex), meaning roughly two-thirds of randomly paired men will score higher than their female counterpart.
The sex difference in people-versus-things career interests was found in 53 out of 53 nations in one study and 80 out of 80 nations in another, making it one of the most cross-culturally universal findings in social science.
Only about 5–10% of mammal species form pair bonds and have biparental care, whereas roughly 90% of bird species do — making humans more like the average bird than the average mammal in their primary reproductive arrangement.
Research has found that average parental grief levels track the reproductive value of the deceased child, peaking when the child is a couple of years past puberty — the age of maximum reproductive value.
In the Clark-Hatfield street study, 75% of men agreed to have sex with an attractive stranger who approached them on campus, while exactly 0% of women agreed to the same offer.
For most of human history, approximately 50% of children born did not survive to reproductive age, making infant mortality one of the greatest causes of misery in human history.
The sex difference in people-versus-things career interests was first documented in 1911 and has remained consistent ever since, predating most modern gender role pressures.
Everyone lists aggression, risk-taking, and parenting when asked about sex differences. Stewart-Williams points out the one that's hiding in plain sight: which sex each sex is attracted to. It has the clearest evolutionary rationale of all, yet it's routinely omitted from academic summaries.
No single piece of evidence proves sex differences are innate. But six independent lines all point in the same direction: early appearance, resistance to cultural pressure, persistence over time, hormonal correlates, cross-cultural universality, and animal homologues. When every arrow points the same way, the case becomes compelling.
Only 5–10% of mammal species form pair bonds and share child-rearing. But roughly 90% of birds do. That puts humans squarely in the bird camp — and the implication is powerful: biparental investment is the primary reason human sex differences are more muted than in most mammals.
The most common misreading of evolutionary psychology is conflating proximate causes (why it feels good) with ultimate causes (why the trait exists). Nobody has sex because they want to pass on their genes. They have sex because it feels good. These are different questions. Confusing them derails half the debates about evolution and behavior.
In the Clark-Hatfield study, a good-looking stranger approached random campus students offering a date, a visit to their room, or immediate sex. For the sex offer: 75% of men said yes, 0% of women did. Men who declined apologised and asked for a rain check. Women who were approached simply reacted with disgust.
The verbal aggression gap between men and women is modest. The physical aggression gap is bigger. For homicide, it's enormous — men perpetrate over 90% of killings in every nation where data exists. The same pattern appears in chimpanzees, where males commit 92% of chimpicides. This is reproductive variance made lethal.
Ashley Madison, the infidelity website, had 20 million active male users and 1,492 active female users — even though women got free lifetime membership and men had to pay. The ratio almost exactly mirrors the global sperm-to-egg production asymmetry discussed earlier in the episode.
The deeper you go into sex differences, the more everything traces back to one thing: variance in offspring number is greater in males. When some males can have many offspring and others have none, selection becomes intense — for aggression, status-seeking, risk-taking, and interest in multiple partners. Females, with a lower ceiling, evolve to be choosier.
Start with same-size gametes and you get an unstable equilibrium. Some gametes get bigger to carry more nutrients; others get smaller and more numerous to outcompete them. The middle disappears. This is how the biological sex binary emerges — and why it appears in virtually every sexually reproducing species on Earth.
Gay men have more casual sex than straight men; lesbians have less than straight women. This isn't a coincidence — it's a natural experiment. Without having to negotiate with the other sex, each group's baseline sexual motivation is exposed. Straight couples are always compromising, with women generally setting the frequency floor.
Critics of the gender equality paradox argue that sex-segregated societies skew self-report data. Stewart-Williams fires back: the paradox also appears in cognitive abilities like spatial reasoning and even in physical traits like height — not just personality surveys. The critique doesn't land.
Social role theory says patriarchy inflates sex differences. The data say the opposite. In the most gender-equal, least patriarchal societies, sex differences in personality and career interests are consistently larger, not smaller. Nobody predicted this — including Stewart-Williams himself.
Israeli kibbutzim tried to replace biological parenting with communal child-rearing to eliminate traditional gender roles. It worked briefly. Then the parents — especially the mothers — revolted. The women agitated more than the men to reclaim direct parenting of their own children, despite the commune's ideology pushing in the opposite direction.
Analysis
What they talk about
- Science 46%
- Society & Culture 39%
- Health & Fitness 15%
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