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A photo of two people in front of depictions of different stages of the embryo
Podcast, 26 mins

Recapitulation Theory: Your inner fish

Do human embryos have gills? Scientists once said yes, proposing embryos pass through stages that mirror the species’ evolutionary history during development.

Part of Good in Theory
16 Apr 2026 09:00

At an early stage of development human embryos have gill-like features. Observations like this prompted scientists to suggest that embryo development copies the evolutionary development of the species.

Their theory became known as recapitulation theory and had the slogan “ontogeny recapitulates phylogeny”. Many scientists, such as Charles Darwin, disagreed with recapitulation theory even though they agreed that embryos of different species share a lot of similarities.

Ultimately as the development of embryos in the womb was better understood recapitulation theory was superseded. Still it left its mark on science, even influencing cognitive research and music theory.

Credits

  • Created and Produced by: Rita Neves (Research Associate at the University of Sheffield)
  • Created and Produced by: Sofie Ried (PhD Student at the University of Sheffield)
  • Intro/Outro Music: Andrew Glover
Correct as of content publication - 16/04/2026

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