Préformation et épigénèse

[Machine translation] According to the Le Robert dictionary, preformation is “one of the two biological theories fighting in the 17th and 18th centuries, according to which the living organism is completely constituted in the germ”. Its opposite is epigenesis, “theory according to which an embryo develops by successive differentiations of new parts”. These are current definitions, which give these two terms a clear-cut meaning, namely the one that is commonly used in biomedical science education. However, their precision obscures the existence of a controversy that lasted much more than two centuries, which saw philosophical and religious principles, then scientific concepts and observations clash in a debate that was finally without a real winner, at least before the middle of the 19th century, at least before the middle of the 19th century, which will enshrine epigenesis in its current definition. The analysis of the entanglement of these different approaches to the problem of reproduction is an example of the place of representations in the construction of scientific knowledge.