The Uncomfortable Science Of Sex Differences - Steve Stewart-Williams - #1120

Could you have released this book six years ago, or was the timing better now that the temperature has cooled?

I could have, but it would have landed worse; the climate is calmer now, which lets us have a clearer conversation.

Why is talking about sex differences still so loaded?

Because of a long history of sexism and bad science, even though many differences are modest, mostly about preferences, and often cast men in a less flattering light; good science corrects the old errors rather than repeating them.

So like how dark political history dogs behavioral genetics, the past shadows this field too.

Exactly, and the antidote to the old prejudice is better evidence, not silence.

Why study sex differences at all?

Because it’s deeply fascinating and clarifying; evolutionary psychology gave me that click-into-place feeling, like finally understanding the phases of the moon.

The moment you admit you’re interested, some people assume you want to hold progress back, when in fact understanding behavior can help build a better society.

My stance is simple: let people be themselves; evolutionary origins are morally neutral, and averages don’t dictate how any person should live.

People worry that evolutionary explanations excuse bad behavior.

We should say clearly that most gaps are modest, there’s huge overlap, and facts aren’t prescriptions; explaining is not excusing.

Stacking lots of small gaps can make two groups feel miles apart though.

Be careful with multivariate stacking; even coin-flip groups will look far apart if you add enough tiny differences.

Let’s define sex—what are we talking about?

Biologically, sex is defined by gametes: males produce small gametes and females produce large gametes; across almost all sexually reproducing species there’s a real binary.

So the two-currency system—sperm and eggs—really is the rule?

Yes; equal-sized gametes are evolutionarily unstable, so selection pushes toward very small, mobile gametes and large, well-provisioned ones, with the middle losing both ways.

What about within-sex variation and intersex conditions—do they overturn the binary?

No; there’s rich variation in traits within each sex, yet almost everyone still produces either sperm or eggs.

How do we tease apart nature and nurture when social roles touch everyone?

Multiple clues point to innate contributions: differences appear very early and often surge at puberty; they persist despite efforts to curb them, especially male aggression; many have held steady across the twentieth century; prenatal hormones predict later traits, as seen in girls with CAH; key patterns show up across cultures; and we see similar sex-linked behaviors in other species facing comparable selection pressures.

Puberty could reflect cultural pressure, but we also see fetal brain differences and early sex gaps long before socialization makes sense.

And cultures usually try to suppress male aggression, not amplify it; prenatal testosterone is linked to higher aggression, risk-taking, and more male-typical interests, including in CAH girls, some of whom also show higher rates of same-sex attraction.

Walk me through why averages must match while variance differs, and why sex ratios don’t skew toward fewer males.

Each child has one mother and one father, so averages align, but males often show greater variance—some have many offspring, some have none; equal sex ratios evolve because if one sex becomes scarce, parents who produce it gain an advantage; in humans, male investment is unusually high, which dampens male variance compared with many mammals.

So those big, meme-able skew numbers are likely overblown.

That’s my view; the skew exists but is smaller in our species because fathers often invest heavily.

There’s that bleak-but-useful idea that grief tracks reproductive value, plus the reminder to separate proximate from ultimate motives.

Right; we don’t consciously compute reproductive value, but our reactions can reflect ancient pressures, and that’s no more demeaning than any purely sociocultural account.

Humans are odd mammals—more like birds—because of pair bonding and shared parenting.

Exactly; most mammals have deadbeat dads, while most birds pair-bond, and we resemble birds on that front; the same evolutionary logic still applies, but our sex differences are muted by biparental care.

What are the biggest gaps?

Physically, upper-body strength and voice pitch diverge a lot; psychologically, the biggest is who each sex is primarily attracted to, and a large one in sex behavior is sociosexuality, where men on average are more open to casual variety, though there’s plenty of overlap.

How do drive, cheating, and casual sex fit the evolutionary story?

Selection favors mating opportunities for men more than women, but in humans that push is toned down by shared parenting; again, explanation isn’t exoneration.

The Ashley Madison numbers screamed that asymmetry; what about men’s stronger response to visual cues?

Both sexes care about looks, but men weight visual fertility cues more because of menopause, which helps explain higher porn use; women’s stronger appetite for romance fiction coexists with the fact that both sexes value long-term love.

Men can be very romantic too, yet content preferences still split; and there’s that sexual overperception bias.

Men more often overread female interest, probably projecting their own level of attraction; it’s a cross-sex mind-reading miss.

Error management helps explain the overreach without excusing it, and same-sex couples reveal baseline wants—how so?

Gay men have more casual sex than straight men, and lesbians have less than straight women, because neither has to compromise with the other sex’s preferences, making the signal cleaner.

In marriages, men often want more sex than they get, which is a quiet, ongoing compromise many women may not notice.

That trade-off likely falls more often on men, though of course some women make the same sacrifice; lesbian couples also report more dead-bedroom issues.

How aligned are mate preferences?

We’re strikingly similar: both want kindness, loyalty, stability, and some attractiveness; men on average place more weight on looks in long-term mates, women more on resources and status, but for short-term flings women’s weight on looks rises to match or even exceed men’s because good-gene cues and quick assessments matter more.

Nightclubs make it obvious: men broadcast status with visible signals, women showcase beauty—our peacock tails rendered in culture.

Yes, and those displays vary by time and place; resource signals can work both ways, but they generally matter more to women.

Sperm-donor choices strip seduction away and reveal pure trait preferences; and on the street, the Clark and Hatfield study showed massive sex gaps in accepting offers.

Date invitations were roughly similar, but many more men agreed to go upstairs, and about three-quarters said yes to sex while zero percent of women did; women’s refusals were sharper, reflecting lower interest and real safety concerns.

Harsh refusals can also come from big mate-value gaps that feel insulting, as if the approacher is downgrading how you see yourself.

Flip it for a second: if a man thinks he is an eight and a three approaches, does he feel slighted or flattered?

Guys tend to overestimate their appeal, so a rare approach often lands as proof of their magnetism rather than an insult.

What do the data say about sex differences in aggression?

Men lead in direct aggression, and the gap widens with severity. Across cultures, roughly nine in ten homicides are by men, and men are often the victims; chimps show a similar pattern.

Why does that gap exist?

Male competition for status and mates has favored greater risk and male‑male aggression, while females gain less from fighting because they cannot multiply offspring the same way and face higher costs.

Women fear violence yet are drawn to men who can wield it; is controlled protectiveness the key?

Capacity without self‑control is a liability, but protectiveness and the ability to switch it off are attractive; muscles can help, yet character matters most.

We found that willingness to protect boosted attraction even more than raw ability; is it worse when a capable man fails to act?

Yes, not stepping in when you clearly can signals poor character, and many would choose a less imposing partner who will show up.

Why the height premium, and does partner size change it given the tall‑woman versus short‑woman debate?

Height sits with strength in the protection bundle, so interest tracks that, and a smaller partner does not reduce the value of a taller defender.

Who stalks or surveils more, and what drives it?

Both sexes can become fixated, but men more often escalate through aggression; jealousy fuels mate‑guarding for different reasons—paternity uncertainty for men and fear of desertion for women.

Cross‑sex mind reading often fails, and men overread interest from female friends; what about sexual violence rates?

Men perpetrate sexual violence far more often; explaining evolutionary roots is not excusing it, and 'natural' is not 'good'.

Coercion exploits male pursuit of no‑strings sex plus a willingness to use force, and it tramples a core value—female choice.

Female choice is fundamental across species, which helps explain why rape is uniquely violating.

Some push for perfect parity, but no one argues for equal homicide rates; equality is not always the target.

The aim is to cut violence, not balance it; shrinking the gap by raising female aggression would make things worse.

Parenting differences keep upsetting people; what does the evidence show, and what did the kibbutz experiment teach us?

Women do more hands‑on care in every measured culture, reflecting average inclinations. When communes tried communal child‑rearing, parents—especially mothers—pushed to bring kids back home; calling that fact an insult reveals that we undervalue caregiving.

Short leave and status pressure mean many mothers miss once‑in‑a‑lifetime milestones, and it is a brutal trade‑off.

Work and family pull both sexes, but the loss tends to hit women harder; many pause careers while kids are young, then ramp back up later.

How do sexual jealousy triggers differ?

Men are more upset by sexual infidelity, women by emotional defection that risks abandonment and resources.

Even decades later, a surprise half‑sibling can reignite jealousy despite no live resource threat, which shows how deep the reaction runs.

What about personality gaps?

Women score higher on neuroticism and agreeableness with small to medium effects; other Big Five differences are minor and mixed.

And the people‑versus‑things divide and the gender‑equality paradox?

One of the largest gaps is interests—men tilt toward things, women toward people—replicated for over a century and across nations. In more egalitarian countries the divergence often grows as preferences can express more freely.

Ecology seems to nudge display and attraction; we see more self‑sexualization where inequality is high—does the feast‑famine 'bigger body in bad times' idea hold?

I buy the inequality‑to‑display link, but I am skeptical that ancient feast‑famine cycles were strong enough to bake in robust size preferences.

Cognitive abilities?

Average IQ is equal; men show slightly more variance, women have a verbal edge, and men a small spatial edge, with most gaps modest and shaped by both biology and culture.

Physical health and lifespan, and that risk‑taking edge?

Men die younger, partly due to testosterone’s costs; in historical samples, prepubertal castration erased the gap. The same risk appetite that drives more foolish deaths also produces more heroism and big wins alongside big wipeouts.

Policy‑wise, hiding data breeds resentment and bad fixes; what is the better approach?

Give people the facts, clear genuine barriers, avoid overstating discrimination, and respect free choice, or you risk backlash and counter‑bias.

What about mental health splits?

Women face more anxiety and depression, men more antisocial disorders, autism, and ADHD, while bipolar is about equal; extremes often reflect costly byproducts of adaptive tendencies near the average.

What goes wrong when we deny or exaggerate sex differences?

Minimizing pushes a unisex straitjacket and blinds medicine to sex‑specific symptoms, while exaggerating fuels stereotypes, hides bidirectional abuse at lower levels, and invites backlash.

You crushed it; plug what you like, and for the record I am a fan of your books and those sharp link rundowns.

Thank you for having me; this was a joy.

Appreciate you, Steve—thanks for making the trip; until next time, goodbye everyone.