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a biological theory, prevalent until the 18th century, according to which the sexual cells of an organism contain a fully formed embryo or parts of an embryo. Its supporters mistakenly rejected the idea that the parts of an embryo were formed during the embryo’s development.

J. Swammerdam, M. Malpighi, and A. Leeuwenhoek were among the first 17th-century microscopists who believed that the embryo was preformed. Ovists believed that preformation occurred in the ovum and animalculists believed it occurred in the sperm. The only changes that would occur during the organisms’ development would be an increase in size and a consolidation of its transparent, formerly invisible parts. In its extreme, preformation was based on creationism, or the dogma of the primordial creation of living beings that contained within themselves the rudiments of the embryos of all future generations. Opponents of spontaneous generation and other mechanistic theories of development, such as C. Bonnet, A. Haller, and L. Spallanzani, continued to substantiate preformation.

The concept that organisms develop as successive neoformations (epigenesis) gained prevalence in the second half of the 18th century. Preformation tended to be disproved by studies on sharp deviations from normal development, on the transmission of individual hereditary characteristics from both the mother as well as the father, and on the ability of the organism to regenerate.

The more primitive concept of preformation should be distinguished from preformism, which arose in the second half of the 19th century.


Gaisinovich, A. E. K. F. Vol’fi uchenie o razvitii organizmov (V sviazi s obshchei evoliutsiei nauchnogo mirovozzreniia). Moscow, 1961.
Roger, J. Les Sciences de la vie dans la pensée française du XVIII siècle: La Generation des animaux de Descartes à l’Encyclopédie, 2nd ed. Paris, 1971.


References in periodicals archive ?
Just as modern, gene-oriented views of reproduction derive from preformation doctrine, modern regulation of abortion derives from a preformationist understanding of the embryo as an essentially complete new being.
environmental policy took a preformationist view of children--to the extent that children were considered at all.
Darwin's jealous and bitter opponent Richard Owen advocated, successively, preformationist and epigeneticist versions of what some people might want to call "evolution." The difference between his views and Darwin's becomes apparent when we consider the ecological implications of the following quotation (Owen 1860, p.
In other words, preformationism involves the claim that "all characters of the adult organism are present in the fertilized egg and only need[] to unfold or grow." (74) Preformationists held that the embryo was already an adult in miniature form, and merely depended on its parents and on its environment to provide the essential nutriment to allow it to develop.
In Kant's era, for example, the central argument in biology was between the 'preformationists', who believed all life existed pre-formed and 'unfolded rather than developed' (p37), and 'epigenesists' who argued that new categories could emerge through environmental 'degeneration' (p39).
Smart's God appears to work in a more flexible, exuberant way than the God of the preformationists, but this too is a question worth exploring further.
These views helped the preformationists hold on to their ideas for almost two more centuries.
Both were preformationists, who believed that "all living things existed preformed inside their forebears in the manner of the Russian doll, put there by God at the beginning of Creation."
23 Gasking describes how the early preformationists were all ovists (48), but beginning with Leeuwenhoek in 1683 animalculists became increasingly popular (56).