Modern WisdomThe Uncomfortable Science Of Sex Differences - Steve Stewart-Williams
CHAPTERS
- 0:00 – 2:05
Why sex differences became a cultural flashpoint (and why the science isn’t sexist)
Chris and Steve open by discussing why a book on sex differences would have landed worse a few years earlier and why the topic triggers such intense moral suspicion. Steve argues the controversy is driven largely by the historical misuse of “science” to justify sexism, even though many real sex differences are modest and morally neutral.
- •Public climate around sex differences has cooled slightly compared to recent years
- •Sex differences are often modest preference gaps, not sweeping ability gaps
- •Historical scientific sexism (e.g., 1800s claims) fuels modern distrust
- •Studying evolved differences doesn’t imply endorsing inequality or disrespect
- •Science can correct past prejudice rather than perpetuate it
- 2:05 – 6:22
Why studying sex differences matters: fascination, self-knowledge, and avoiding the naturalistic fallacy
Steve explains why sex differences are worth studying: they’re intrinsically fascinating and practically useful for understanding ourselves and designing better institutions. They stress that evolutionary explanations are descriptive, not prescriptive—understanding causes doesn’t justify behaviors.
- •Evolutionary psychology as a “click” explanation for human behavior
- •Studying sex differences can help steer society more intelligently
- •“Let people be themselves” as a guiding moral stance
- •Naturalistic fallacy: evolved/natural ≠ good, bad, or permissible
- •Within-sex variation and overlap matter as much as mean differences
- 6:22 – 7:55
Multivariate sex differences: why stacking small gaps can mislead
Chris raises the idea that many modest differences may add up to large separations between the sexes. Steve cautions that multivariate clustering can exaggerate perceived differences, since even random group splits can look highly distinct when you stack many small trait gaps.
- •“Multivariate sex differences” and the intuition of two distinct clusters
- •Stacking many small differences can inflate perceived separation
- •Randomly divided groups can also look different via multivariate stats
- •Single-trait thinking is often more relevant than multivariate composites
- •A warning against overclaiming magnitude from statistical artifacts
- 7:55 – 13:21
What sex is (biologically): gametes, anisogamy, and why exceptions don’t erase the binary
Steve lays out the biological definition of sex in terms of gamete size: sperm vs eggs. They discuss anisogamy’s evolutionary logic, why isogamy is unstable, and why intersex variation doesn’t invalidate the underlying sex binary in sexually reproducing species.
- •Sex defined by gamete size: males produce sperm, females produce eggs
- •Anisogamy vs isogamy and why isogamy tends to break apart
- •Why mid-sized gametes are evolutionarily unstable (barbell logic)
- •Within-sex variation and intersex conditions don’t negate binary categories
- •Large reproductive-number asymmetries start with gamete economics
- 13:21 – 19:47
Biology vs socialization: six clues that sex differences aren’t ‘just culture’
They tackle the hardest methodological issue: separating innate influences from socialization when all humans grow up in gendered cultures. Steve outlines multiple converging lines of evidence (early emergence, puberty shifts, persistence, hormonal links, universality, and cross-species parallels) that together suggest biology contributes meaningfully to many differences.
- •Sex differences can appear very early (before plausible heavy social shaping)
- •Puberty-linked “skyrocketing” suggests hormonal/biological components
- •Some gaps persist despite cultural pressure to reduce them
- •Prenatal testosterone correlates and CAH evidence
- •Cross-cultural recurrence and parallels in other species as cumulative evidence
- 19:47 – 21:37
How much do parents shape boys vs girls? Behavioral genetics and limits of ‘parenting explains it’
Steve evaluates sociocultural explanations that do hold water while questioning how much parents alone can account for observed gaps. He highlights findings from behavioral genetics (e.g., identical twins) suggesting shared home environment has weaker long-run effects than many assume—complicating simple “parenting causes sex differences” narratives.
- •Parents often don’t treat sons and daughters as differently as presumed
- •Second law of behavioral genetics: shared environment effects fade in adulthood
- •Why this challenges parent-driven accounts of sex differences
- •Cross-cultural variability exists, but doesn’t imply ‘all culture’
- •Sociocultural causes are real—just often overestimated
- 21:37 – 26:39
The gender-equality paradox: why some differences grow in freer societies
They explore the counterintuitive pattern that sex differences sometimes increase—not decrease—in more gender-equal countries. Steve reviews proposed rebuttals (e.g., self-report comparison effects) and notes the paradox also appears in some cognitive and even physical traits, making it harder to dismiss as mere reporting bias.
- •Social role/patriarchy theories predict smaller gaps in egalitarian societies
- •Empirical pattern often shows larger gaps where gender equality is higher
- •Possible explanation: sex-segregated societies distort self-comparisons
- •Counterpoint: paradox appears beyond self-report (e.g., spatial ability, height)
- •Implication: freedom can amplify preference-driven sorting
- 26:39 – 29:02
Biggest differences overall: anatomy, strength, voice—and the ‘obvious’ psychological difference people forget
Steve distinguishes between massive physical differences (reproductive anatomy, upper-body strength, voice pitch) and generally smaller psychological ones. He argues the biggest psychological sex difference is rarely named because it’s too obvious: each sex is primarily attracted to the other.
- •Largest gaps are physical: reproductive anatomy and upper-body strength
- •Voice pitch dimorphism is unusually large compared to other apes
- •Most psychological differences are moderate with large overlap
- •Biggest psychological difference: primary sex of attraction
- •Why ‘obvious’ differences are sometimes omitted in scientific summaries
- 29:02 – 32:42
Sex differences in sex: casual sex, porn, projection errors, and the logic of male overperception
They dig into sociosexuality—men’s higher average interest in casual sex and variety—and why the gap exists yet still shows overlap. The conversation spans porn vs romance consumption, sexual overperception bias, and how ‘smoke detector’ logic can produce systematic misreadings without excusing bad behavior.
- •Sociosexuality gap: men higher on average, but far from absolute
- •Why visual stimuli matter more for men (youth/fertility cues, menopause)
- •Women’s stronger romance/romantasy interest: intriguing and less settled
- •Sexual overperception bias: men more likely to infer interest that isn’t there
- •Smoke detector principle: asymmetric costs of missed vs false opportunities
- 32:42 – 54:41
Where sex differences come from: reproductive variance, Bateman/Trivers, and parental investment
Steve grounds sex differences in evolutionary fundamentals: males often have higher potential reproductive variance, selecting for risk-taking, competition, and mating effort. They clarify why averages must match across sexes (“it takes two”) while variance differs, and how biparental care in humans ‘nerfs’ some classic mammalian gaps.
- •Reproductive variance (not average) drives many evolved differences
- •Bateman’s principle and Trivers’ parental investment refinement
- •Why sex ratios tend toward 50/50 via individual-level selection
- •Parental investment sets ceilings on offspring number and choosiness
- •Humans’ biparental care reduces—without eliminating—many differences
- 54:41 – 1:14:13
Humans in the animal kingdom: pair-bonding ‘like birds,’ size dimorphism, and why males are often bigger
They ask whether human sex differences are unique and land on ‘yes and no’: humans are unusual among mammals for pair-bonding and paternal care, but not exempt from general evolutionary rules. They also discuss exceptions like insects/spiders where females are bigger, and how ecological and reproductive pressures shape dimorphism.
- •Humans are rare among mammals: durable pair bonds and paternal investment
- •In reproductive strategy, humans resemble many birds more than mammals
- •Lower human reproductive skew compared to typical mammals
- •Female-larger species: selection for egg production capacity
- •Male-larger mammals: intrasexual competition and fighting ability
- 1:14:13 – 1:29:21
Mate preferences: how similar we are, where we differ, and why status/looks shift by relationship context
Steve emphasizes large common ground in mate preferences (kindness, intelligence, mutual attraction) while identifying reliable average differences. They explain why looks matter more to men in long-term contexts, why women weight status/resources more in long-term contexts, and why women’s emphasis on looks rises in short-term mating where “genes” loom larger than investment.
- •Shared priorities dominate: kindness, intelligence, stability, attraction
- •Long-term: men weight looks somewhat more; women weight resources/status more
- •Short-term: women’s emphasis on physical attractiveness increases markedly
- •Status as both investment capacity and possible fitness indicator
- •Sperm-donor and on-the-street studies as windows into preference structure
- 1:29:21 – 1:52:10
Aggression, stalking, and sexual violence: consistent gaps, escalating at extremes, and ‘analysis ≠ justification’
They map how sex differences in aggression grow larger as behaviors become more severe—from verbal aggression to homicide. Steve discusses stalking as a distorted extension of mating effort and addresses sexual violence carefully, arguing evolutionary accounts can explain risk patterns without excusing harm.
- •Aggression gap increases with severity: verbal < physical < violent crime < homicide
- •Male perpetration rates are remarkably cross-culturally consistent
- •Parallels with chimpanzees in the sex ratio of lethal aggression
- •Stalking as maladaptive/antisocial pursuit behavior more common in men
- •Sexual coercion: linked to mating effort + aggression; explanation isn’t endorsement
- 1:52:10 – 1:58:59
Parenting differences and the kibbutz case study: when egalitarian ideals collide with parental instincts
Steve argues sex differences in parenting are universal and controversial partly because people read them as moral prescriptions. They discuss the ‘soft bigotry of male expectations’ and the kibbutz experiments, where communal child-rearing often broke down under parental resistance—especially from mothers—suggesting some caregiving preferences persist despite ideology.
- •Across cultures, women do more direct caregiving though men invest unusually much for mammals
- •Parenting differences trigger moral anxiety more than aggression differences
- •‘Soft bigotry of male expectations’: male-typical becomes the default ideal
- •Kibbutz communal childcare: parents (especially mothers) resisted and reversed it
- •Work–family tradeoffs and why policy debates often miss emotional realities
- 1:58:59 – 2:03:29
Jealousy, mate-guarding, and paternity uncertainty: why men and women fear different betrayals
They examine sex differences in jealousy: men are more upset by sexual infidelity, women more by emotional infidelity—on average—given different adaptive risks (paternity uncertainty vs desertion). The discussion extends to surveillance/mate-guarding and how evolved “gut” reactions can misfire in modern contexts (e.g., decades-late paternity discoveries).
- •Male jealousy prioritizes sexual infidelity; female jealousy prioritizes emotional infidelity
- •Paternity uncertainty as a uniquely male adaptive problem
- •Female risk of desertion and being ‘left holding the baby’
- •Mate-guarding behaviors: monitoring, suspicion, and modern ‘surveillance’
- •Proximate vs ultimate explanations help explain irrational-seeming reactions
- 2:03:29 – 2:26:20
Personality, interests, cognition, and health: where differences are real, modest, or mainly about variance
Steve surveys sex differences in Big Five traits (notably neuroticism and agreeableness), the large people-vs-things interest divide, and the contested terrain of cognitive abilities. They also cover sex-linked patterns in physical health, lifespan, and mental health—highlighting both average differences and how ignoring them can harm diagnosis and care.
- •Big Five: women higher on average in neuroticism and agreeableness (modest gaps)
- •People-vs-things interests show one of the largest psychological differences cross-culturally
- •Cognition: no average IQ difference; small ability gaps and slightly higher male variance
- •Health: men die younger; testosterone as a tradeoff; sex differences in disease presentation
- •Mental health: women more depression/anxiety; men more antisocial traits; mixed/unknown causes for some disorders
- 2:26:20 – 2:32:35
Policy and culture: harms of denying differences vs exaggerating them (and how both distort society)
Steve argues the debate is lopsided: people rightly fear exaggerating sex differences, but denying them creates its own harms—from unrealistic ‘unisex’ expectations to flawed explanations of workplace gaps. He also notes medical and social consequences when sex differences are ignored or overstated, and how misattribution can fuel resentment and counterproductive interventions.
- •Denying differences can replace gender roles with a ‘unisex straitjacket’
- •Over-attributing occupational gaps to discrimination can misdirect interventions
- •Ignoring sex differences can worsen health outcomes via misdiagnosis
- •Exaggerating differences can cause neglect of minority cases (e.g., male depression)
- •Both extremes can generate backlash and worsen trust in institutions
- 2:32:35 – 2:33:38
Closing: Steve’s book, Substack, and where to find more
They wrap with Chris praising the book and Steve sharing where listeners can follow his work. Steve highlights his Substack as his main outlet and they close the conversation warmly.
- •Book plug: A Billion Years of Sex Differences
- •Substack plug: ‘Nurtured’ newsletter and link roundups
- •Chris’s recommendation of Steve’s previous work
- •Final thanks and sign-off
