[Revised entry by Melinda Bonnie Fagan and Jane Maienschein on August 29, 2026.
Changes to: Main text, Bibliography]
Development is a central biological process, and ideas about its nature have been influential in biological thought. This entry surveys the history of these ideas through the lens of “epigenesis vs. preformation”. Epigenesis is, roughly, the thesis that every developing entity starts from material that is unformed, with form emerging gradually, over time, in the process of development. Preformation, in contrast, is the thesis that development begins with the entity in some way already preformed, or predelineated, or…

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