PREFORMIZM

From Big Medical Encyclopedia

PREFORMIZM (Latin praeformare to form in advance) — the biological doctrine, according to Krom sex cells support the material structures which are unambiguously predetermining an ontogeny and signs of an organism. In narrow value carry the concepts assuming existence in sex cells in a miniature of the created organism which in the course of an ontogeny only increases in sizes to P.

P.'s sources can be found already in ancient philosophy, in the form of ideas of «seeds of the things» comprising all infinity of the qualities existing in the nature («all in everything»). So, Anaksagor considered that in a human seed are put in is invisible the small sizes hair, kidneys, vessels, sinews and bones which in process only connect and grow. The similar ideas were introduced also by Hippocrates. Similar views were criticized by Aristotle who created the doctrine about epigenesis (see), according to Krom separate bodies of a germ develop from unstructured substance of an oosperm by a consecutive number of transformations.

In biology in 17 and in the first half 18 accusative hold a dominant position. Such famous scientists as A. Levenguk, J. Swammerdam, M. Malpigi, A. Galler, Bonnet were his supporters (Ch. Bonnet), etc. G. W. Leibniz and N. Malebranche tried to give philosophical justification of P. Ideological basis of preformistsky concepts was the mechanistic understanding of the idea of development dominating in natural sciences of that time as purely quantitative increase (growth) in parts without their high-quality reorganization. On the other hand, distribution of a preformizm was promoted by low level of knowledge in the field of embryology. Really, without having detailed data on development of a germ, it is difficult to present how there is a formation of extremely difficult organism from seeming «shapeless» for the observer-microscopist of a germinal rudiment. Therefore process of an ontogeny from a stage of a germ to a stage of a mature organism, according to the preformistsky doctrine, consisted in increase and consolidation transparent at early stages of an embryogenesis and the parts of a body, invisible under a microscope, which are completely created already in sex cells. In turn, for an explanation of «mechanism» of formation of a germ in a sex cell the theory of «investment» was used, according to a cut already the first organisms created allegedly by god bore in themselves rudiments of germs of all future generations.


Depending on where on their representations was preformirovan a germ (in an ovum or a spermatozoon) preformists were divided into so-called ovist and animalkulist.

P.'s influence was not limited to limits of embryological researches. In the all-biological plan of his idea were used as confirmation of the idea of an invariance of life-forms dominating in 17 — 18 centuries which were allegedly created by god (see. Creationism ).

Difficulties of an explanation from positions P. of the fact of transfer by inheritance of individual signs as from the father that contradicted views of ovist, and from mother that did not keep within the concept of animalkulist, and also results of hybridization and a phenomenon of regeneration seriously undermined its scientific positions. The last circumstance promoted distribution in biology from the second half of 18 century of the epigenic concept (see. Epigenesis ), a cut K.-F. Wolf gave detailed experimental justification. For the proof of an inaccuracy of the preformistsky doctrine K.-F. Wolf showed that the intestinal channel is formed at a chicken owing to separation from a belly surface of a germ of a layer of fabric, at first a shaped fillet, and further closed in the closed tube. Therefore, intestines do not exist at early stages of embryonic development, and form at a certain stage again from indifferent tissues of a germ, i.e. according to the concept of epigenesis. Proceeding from this observation as a starting point, K.-F. Wolf put forward the epigenic theory, having extended it to all bodies.

In the primitive form P. it was disproved in connection with achievements of embryology of 19 century, especially after works of K. M. Ber who opened a blastula and described development of systems of bodies of vertebrata from germinal leaves. Disclosure in the second half of 19 century of essence of processes fertilisations (see), meiosis (see) and mitosis (see) made obvious and insolvency of epigenic ideas of germinal development of unstructured substance of an ovum under the influence of external influences that promoted revival of some preformistsky ideas, but already in significantly the rethought look. L. R. Lankester, Uitmen (Ch. Whitman), the Slave (K. Rabl) and other embryologists make a number of hypotheses, according to the Crimea development of a germ is unambiguously determined by any material structures localized in egg. For example, W. His considered certain sites of an ovum as rudiments of these or those bodies.

In close connection and practically along with preformistsky concepts in embryology of the idea of P. gain distribution in hypothetical theories heredities (see), and also autogenic theories of evolution, coming from representations about purely internal (i.e. localized in sex cells) the reasons of both individual, and historical development of organisms. An example of preformistsky attempt of interpretation of evolution is the hypothesis «presence — absence» W. Bateson, according to a cut evolutionary development of organisms comes down to gradual loss of genes which were allegedly already concluded in a genotype of the first organisms which appeared on the earth.

Development biol. and medical sciences, first of all geneticists (see), molecular biology (see) and embryology, actually eliminated P. from the scientific address. Experimental development of the principles of origin and development of live organisms led to ideas of extremely complex structure of hereditary material — genes, about ambiguously determined process of growth and development of an organism at all stages of ontogenesis. Use of these genetic researches in knowledge of organic evolution, synthesis of data of genetics with the idea of an evolutionism significantly limited distribution of preformistsky concepts. Nevertheless and today it is possible to find P.'s influence on development of some problems of an ontogeny and closely related problems of evolution in the form of unilateral exaggeration of a role of «internal» (genetic) factors. Concepts of an orthogenesis and finalistsky theories of evolution — the evident certificate of effects of influence of preformistsky thinking (see. Theory of evolution ). The modern theory of organic development, allowing existence of preformirovanny structures (genome), considers also epigenic factors of implementation of genetic information.


Bibliography:

Gaysinovich A. E., K. F. Wolf and the doctrine about development of organisms, M., 1961; History of biology since the most ancient times up to now, under the editorship of S. R. Mikulinsky and L. Ya. Blyakher, t. 1 — 2, M., 1972 — 1975; Mayr E. A zoological look and evolution, the lane with English, M., 1968; It is equal to X. An oogenesis, Accumulation of morphogenetic information, the lane with English, M., 1964, bibliogr.; Svetlov P. G. Physiology (mechanics) of development, t. 1 — 2, L., 1978; That Kean B. P. General embryology, M., 1977; At about d-dington K. Morfogenez and genetics, the lane with English, M., 1964; Shmalgauzen I. I. Problems of Darwinism, L., 1969; Bateson W. MendePs principies of heredity, Ca-mbridge, 1909.


And. H. Smirnov.

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