A tiny person inside a sperm, as drawn by Nicolaas Hartsoeker in 1695Jan Swammerdam, Miraculum naturae sive uteri muliebris fabrica, 1729
In the history of biology, preformationism (or preformism) is a formerly popular theory that organisms develop from miniature versions of themselves. Instead of assembly from parts, preformationists believed that the form of living things exist, in real terms, prior to their development.[1] Preformationists suggested that all organisms were created at the same time, and that succeeding generations grow from homunculi, or animalcules, that have existed since the beginning of creation, which is typically defined by religious beliefs.
Epigenesis[2] (or neoformism),[3] then, in this context, is the denial of preformationism: the idea that, in some sense, the form of living things comes into existence. As opposed to "strict" preformationism, it is the notion that "each embryo or organism is gradually produced from an undifferentiated mass by a series of steps and stages during which new parts are added" (Magner 2002, p. 154).[4] This word is still used in a more modern sense, to refer to those aspects of the generation of form during ontogeny that are not strictly genetic, or, in other words, epigenetic.
Apart from those distinctions (preformationism-epigenesis and genetic-epigenetic), the terms preformistic development, epigenetic development and somatic embryogenesis are also used in another context, in relation to the differentiation of a distinct germ cell line. In preformistic development, the germ line is present since early development. In epigenetic development, the germ line is present, but it appears late. In somatic embryogenesis, a distinct germ line is lacking.[5] Some authors call Weismannist development (either preformistic or epigenetic) that in which there is a distinct germ line.[6]
The historical ideas of preformationism and epigenesis, and the rivalry between them, are obviated by the contemporary understanding of the genetic code and its molecular basis together with developmental biology and epigenetics.
^Maienschein, Jane, "Epigenesis and Preformationism", The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.).
^According to the Oxford English Dictionary:
The word is used by W. Harvey, Exercitationes 1651, p. 148, and in the English Anatomical Exercitations 1653, p. 272. It is explained to mean 'partium super-exorientium additamentum', 'the additament of parts budding one out of another'.
It is also worth quoting this adumbration of the definition given there (viz., "The formation of an organic germ as a new product"):
theory of epigenesis: the theory that the germ is brought into existence (by successive accretions), and not merely developed, in the process of reproduction. ... The opposite theory was formerly known as the 'theory of evolution'; to avoid the ambiguity of this name, it is now spoken of chiefly as the 'theory of preformation', sometimes as that of 'encasement' or 'emboîtement'.
^Callebaut, Marc, 2008: Historical evolution of preformistic versus neoformistic epigenetic thinking in embryology. Belgian Journal of Zoology 138(1): 20-35.
^Magner, Lois. A History of the Life Sciences. New York: Marcel Dekker, Inc, 2002
^Buss, L.W. (1987). The Evolution of Individuality. Princeton University Press, Princeton, NJ, p. 20 [1].
^Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 295-297.
denial of preformationism: the idea that, in some sense, the form of living things comes into existence. As opposed to "strict" preformationism, it is the...
creation of a miniature, fully formed human. The concept has roots in preformationism as well as earlier folklore and alchemic traditions. The term lends...
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Three variants of preformationism were homoiomerous preformationism, anhomoiomerous preformationism, and homuncular preformationism. According to the...
software package from 3D printing technology company Formlabs Perform Preformationism, a theory that organisms develop from miniature versions of themselves...
Harvey (1578–1657), was a rejection of spontaneous generation and preformationism as well as a bold assumption that mammals also reproduced via eggs...
which mating produced children were not understood. The theory of preformationism was popular in Ancient Greece and Christendom for centuries. Because...
being animalcules (little animals), probably due to his belief in preformationism, which thought that each sperm contained a fully formed but small human...
in the 18th century. The Doctrine of Epigenesis and the Doctrine of Preformation were two distinct views of the understanding of heredity. The Doctrine...
differentiation of individuals according to their "organic preformation". By "organic preformation" he meant that which "gathers, preserves, and refines one's...
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theory of preformation, see this: Jane Maienschein. "Epigenesis and Preformationism". Stanford Encyclopedia of Philosophy. Retrieved 31 January 2011. A...
1725(1725-12-10) (aged 69) Utrecht, Utrecht, Netherlands Known for Contributions to microscopy, preformationism Scientific career Fields Mathematics Physics Biology...
theory (see also fetal origins of adult disease, genomic imprinting). Preformationism – the theory that all organisms have existed since the beginning of...
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speculated that organisms were already preformed in the seed (theory of preformation), that is in the human a homunculus was already sitting in the sperm...
HaLevi described dominant and recessive genetic traits in The Kuzari. The preformation theory is a developmental biological theory, which was represented in...
removed. In spite of his scientific background, Spallanzani endorsed preformationism, an idea that organisms develop from their own miniature selves; e...
calculus. Malebranche also developed an original theory related to preformationism, postulating that each embryo probably contained even smaller embryos...
in was one that treated the competing theories of generation (i.e. preformationism and epigenesis). His account of life involved spontaneous generation...
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particularly to the arguments between proponents of epigenesis and preformation, but satisfactory results could not be achieved. As a master of micro-surgical...
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