preformation

pre·for·ma·tion

P0521100 (prē′fôr-mā′shən)n.1. The act of shaping or forming in advance; prior formation.2. A theory popular in the 1700s that all parts of an organism exist completely formed in the germ cell and develop only by increasing in size.

preformation

(ˌpriːfɔːˈmeɪʃən) n1. the act of forming in advance; previous formation2. (Biology) biology the theory, now discredited, that an individual develops by simple enlargement of a fully differentiated egg cell. Compare epigenesis¹

pre•for•ma•tion

(ˌpri fɔrˈmeɪ ʃən)

n. 1. previous formation. 2. a former biological theory that the individual preexists fully formed in the germ cell and grows from microscopic to normal proportions during the embryo phase. [1725–35]

preformation

the theory that germ cells contain every part of the future organism in miniature form, future development being only a matter of increase in size. Cf. epigenesis.See also: Biology

Thesaurus

Noun

preformation - a theory (popular in the 18th century and now discredited) that an individual develops by simple enlargement of a tiny fully formed organism (a homunculus) that exists in the germ celltheory of preformationtheory - a well-substantiated explanation of some aspect of the natural world; an organized system of accepted knowledge that applies in a variety of circumstances to explain a specific set of phenomena; "theories can incorporate facts and laws and tested hypotheses"; "true in fact and theory"

Translations

preformazione

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

preformation

pre·for·ma·tion the·o·ry

archaic theory that the embryo was fully formed in miniature within a gamete at the time of conception.
See also: homunculus. Compare: epigenesis. Synonym(s): emboitement, incasement theory

preformation

(prē′fôr-mā′shən)n.1. The act of shaping or forming in advance; prior formation.2. A theory popular in the 1700s that all parts of an organism exist completely formed in the germ cell and develop only by increasing in size.

preformation

(prē-fawr-mā′shŭn) In embryology, the development of structures from pre-existing templates, e.g., of bones from cartilage templates.

preformation

Related to preformation: Preformation theory

noun

Synonyms for preformation

noun a theory (popular in the 18th century and now discredited) that an individual develops by simple enlargement of a tiny fully formed organism (a homunculus) that exists in the germ cell

Synonyms

theory of preformation

Related Words

theory