Modern Wisdom
Modern Wisdom

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

July 6, 2026

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5 min read

The Uncomfortable Science Of Sex Differences

Steve Stewart-Williams, author of A Billion Years of Sex Differences, joins Chris Williamson to explain why the study of sex differences remains one of the most controversial—and most illuminating—areas of science. The conversation ranges from the biological definition of sex to the gender equality paradox, mate preferences, aggression, parenting, and the risks of both exaggerating and denying sex differences.

Why the Topic Is So Controversial

Stewart-Williams traces the discomfort around sex differences to a long history of scientific sexism. He cites the 19th-century scientist Gustave Le Bon, who wrote that intellectually accomplished women are "about as rare as a two-headed gorilla." That legacy makes people nervous that any discussion of evolved sex differences will open the door to that kind of thinking. But Stewart-Williams argues the opposite: "Science is the solution to the early sexism rather than a continuation of it." The actual data show modest differences, lots of overlap between the sexes, and no normative implications—something being evolved or natural does not make it good or bad.

The Biological Foundation: Gametes and Parental Investment

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What you'll learn

  • 1 (00:00) **Why Sex Differences Are So Controversial** - The historical baggage of sexist science and the fear that studying differences will justify discrimination.
  • 2 (02:10) **Why Study Sex Differences?** - The deep fascination and practical importance of understanding evolved differences.
  • 3 (08:04) **Defining Sex: The Gamete-Size Binary** - The biological definition of sex based on anisogamy (sperm vs. eggs).
  • 4 (13:24) **Six Lines of Evidence for Innate Sex Differences** - How we know it's not just socialization.
  • 5 (33:58) **The Ultimate Cause: Maximum Offspring Number & Bateman's Principle** - Why sex differences exist in the first place.
  • 6 (43:19) **Reproductive Skew in Humans** - How biparental care "nerfs" the typical mammalian sex differences.
  • 7 (48:31) **The Grief Curve & Reproductive Value** - Why the death of a child near puberty is evolutionarily the most painful.

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Show Notes

Steve Stewart-Williams is an evolutionary psychologist, a professor, and an author.

Why is it so difficult to talk about the differences between men and women today? It's important to recognize that men and women deserve equal respect and opportunity, but that does not mean they are exactly the same. There are differences between the sexes that can be meaningful, valuable, and even beautiful. So what are those differences, and why has discussing them become so polarising?

Expect to learn why talking about sex differences is so controversial, what the actual definition of sex is, why there are challenges to the binary idea of sex, the largest sex differences between men and women, how sex differences reveal themselves via personality, the danger of denying and/or not respecting the differences in sex, and much more…

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Timestamps:

(00:00) Why Sex Differences Are So Controversial (02:07) Why Sex Differences Matter (07:55) What Actually Is Sex? (13:21) Biology vs Society: What Shapes Sex Differences? (19:50) How Much Do Parents Impact Sex Differences? (21:37) The Gender Equality Paradox (26:39) The Top Difference Between Men and Women (29:02) What Is the Biggest Sex Difference? (39:44) Is Parental Investment Damaging? (42:18) Do Men Have Greater Reproductive Success? (50:14) The Hidden Motivations Behind Behaviour (54:34) Are Human Sex Differences Unique? (01:00:07) Is It All About Reproducing? (01:03:20) Why Women Prefer Reading Porn (01:11:44) Are Men and Women Compromising on Sex? (01:14:13) How Similar Are Male and Female Mate Preferences? (01:16:55) How Status and Wealth Shape Attraction (01:21:55) Would Women Sleep With Their Ideal Sperm Donor? (01:29:21) Why Are Women Attracted to Dangerous Men? (01:37:34) Is Height Really That Important? (01:40:25) Do Men Actually Talk More Than Women? (01:46:54) Why Do Men Choose to Be Sexually Violent? (01:52:11) Are Women Naturally More Nurturing? (01:58:59) Who Gets More Jealous in Rela

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