Modern Wisdom

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

Explore episode Jul 6, 2026

Where this was said

What Actually Is Sex?

At 13:06 · chapter starts 7:55

Chris asks what sex actually is, and Stewart-Williams cuts straight to the scientific definition: sex is defined by gamete size. Organisms that produce small gametes are male; those that produce large gametes are female. This is not just a generalisation — it is a definitional truth that holds across almost every sexually reproducing species. The podcast then digs into why this binary is evolutionarily inevitable. Start with same-sized gametes (isogamy) and you get an unstable equilibrium: some gametes are selected to carry more nutrients (getting bigger), while others are selected to be tiny and numerous to seek out the larger ones. The medium-sized gametes — neither big enough to survive well nor small enough to be produced in huge numbers — go extinct. The result is always a barbell: eggs and sperm, females and males. A ChatGPT lookup provides comic illustration: global human sperm production is approximately 200 quadrillion, versus 70 million eggs.

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