The Nature-Nurture-Nietzsche Newsletter

The Nature-Nurture-Nietzsche Newsletter

Keeping It Casual, Part 2

The nature and nurture of sex differences in sexual psychology

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Steve Stewart-Williams
Apr 23, 2026
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Across cultures and centuries, men have shown a stronger interest in casual sex and sexual variety than women. Or so says common wisdom. But is common wisdom right?

In the first post in this series, I argued that it is. In this post, I’ll tackle the harder question: Where do the differences come from? Are they purely products of social pressure, double standards, and patriarchy - or do they run deeper than that?

Long story short, the evidence points strongly toward the latter. Among other things, sex differences in sexual psychology are stubbornly persistent over time, consistent across cultures, and - most tellingly - mirrored in other species, from baboons to hedgehogs to fruit flies. That’s hard to blame on the patriarchy.

If you want to understand what really drives one of the largest and most debated differences in human psychology, read on.

This post is an excerpt from my forthcoming book A Billion Years of Sex Differences. You can access the full collection of excerpts here, and preorder the book here (UK) or here (US).

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