Preformation


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Preformation

 

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.

REFERENCES

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.

A. E. GAISINOVICH

References in periodicals archive ?
The continuity between preformation and modern genetic determinism can be seen in the metaphors that continue to influence our understanding of reproduction today.
Just as the early version of preformation gave way to more nuanced genetic determinism, today's science is not Aristotle's epigenesis.
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.
107) This is a classic statement of preformation doctrine, made shortly before the advent of genetic determinism.
Genera in the Chloroleucon alliance also apparently exhibit some degree of shoot preformation (sensu Brown & Sommer, 1992), which is character 4 in the data set; that is, many of the metamers with associated unit inflorescences form at the end of growth of the current RGU, have some period of dormancy in a perulate bud, and then extend during formation of the next RGU.
Instead of dismissing this theory as an irrational curiosity, she examines preformation with a refreshing mixture of excitement, reverence, and marvel.
Briefly, preformation posited "that all living beings existed preformed inside their forebears in the manner of a Russian doll, put there by G-d at the beginning of Creation with a precise moment established for each one to unfold and come to life" (p.
Pinto-Correia avoids a chronological account of the development of preformation, rather structuring the book around each of the challenges to preformation in general, illustrating how ovists and spermists responded differently.
Transfers within two years of each other (except as noted for reasonable guaranteed payments, preferred returns, operating cash flow distributions and preformation expenditures).
In elaborating his ideas about semen and its causal powers, Aristotle moves as far as possible away from the materialisms of pangenesis and preformation.
On the other hand, if there is something in the fetation from the start that forms it, Aristotle is then dangerously close to the pangenesis and preformation theories which hold that the miniaturized creature or the parts of the creature are already in the generative fluid.
An explanation is required here to meet the suspicions of the partisans of pangenesis and preformation.