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evolution

evolution (ev-o-lu´shun)

A continuing process of change from one state, condition or form to another. 2. A progressive distancing between the genotype and the phenotype in a line of descent. [L. e-volvo, pp. -volutus, to roll out]
biologic e. the doctrine that all forms of animal or plant life have been derived by gradual changes from simpler forms and ultimately unicellular organisms.organic e;
chemical e. the theory of the process by which life arose from inorganic matter.
coincidental e. concerted e
concerted e. the ability of two related genes to evolve together as though constituting a single locus.coincidental e;
convergent e. the evolutionary development of similar structures in two or more species, often widely separated phylogenetically, in response to similarities of environment; for example, the wing-like structures in insects, birds, and flying mammals.
Darwinian e. the proposition that the phylogeny of all species is wholly ascribable to the combined effects of random variation (mutation) in genotypes of the members of a stock as a result of the operation of undirected accidents with consequences to their phenotypes and the operation of preferential (but by no means certain) survival of those resulting phenotypes most suited to survive in the contemporary environment. The proposed system survives largely because of genetic factors that avidly conserve the ontogeny of the stock.
Denman's spontaneous e. a mechanism of spontaneous molding of the fetus and impaction of the shoulder with prolapse of the arm noted in some cases of transverse lie; vaginal delivery is achieved with the breech appearing at the vulva immediately after the prolapsed shoulder.
divergent e. the process by which a species or gene product gives rise to two or more different products.
Douglas' spontaneous e. a mechanism whereby molding of the fetus and impaction of the shoulder and prolapsed arm occurs in transverse lie, allowing vaginal delivery with the lateral aspect of the thorax following the prolapsed shoulder.
emergent e. appearance of a property in a complex system e.g., organism that could have been predicted only with difficulty, or perhaps not at all, from a knowledge and understanding of the individual genotype changes taken separately.
organic e. biologic e
saltatory e. the theory that e. of a new species from an older one may occur as a large jump, such as a major repatterning of chromosomes, rather than by gradual accumulation of small steps or mutations. Cf. emergent e.
spontaneous e. the unaided delivery of the fetus from a transverse lie.

 

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