| Darwinian evolution | 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. (05 Mar 2000) |
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| darwinian | Pertaining to Darwin; as, the Darwinian theory, a theory of the manner and cause of the supposed development of living things from certain original forms or elements. This theory was put forth by Darwin in 1859 in a work entitled "The Origin of species by Means of Natural Selection." The author argues that, in the struggle for existence, those plants and creatures best fitted to the requirements of the situation in which they are placed are the ones that will live; in other words, that Nature selects those which are survive. This is the theory of natural selection or the survival of the fillest. He also argues that natural selection is capable of modifying and producing organisms fit for their circumstances. See Development theory, under Development. Origin: From the name of Charles Darwin, an English scientist. Source: Websters Dictionary (01 Mar 1998) |
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| darwinian ear | An auricle in which the upper border is not rolled over to form the helix, but projects upward as a flat, sharp edge. (05 Mar 2000) |
| darwinian reflex | The tendency of young infants to grasp a bar and hang suspended. Compare: grasping reflex. (05 Mar 2000) |
| darwinian theory | The theory of the origin of species and of the development of higher organisms from lower forms through natural selection (survival of the fittest in the struggle for existence), and of the evolution of humans from an ancestor common to himself and the apes. (05 Mar 2000) |
| darwinian tubercle | A small projection from the upper end of the posterior portion of the incurved free margin of the helix. Synonym: tuberculum auriculae, darwinian tubercle, tuberculum superius. (05 Mar 2000) |
| biologic evolution | Biologic evolution was contrasted with cultural evolution in 1968 by A.G. Motulsky who pointed out that biologic evolution is mediated by genes, shows a slow rate of change, employs random variation (mutations) and selection as agents of change, new variants are often harmful, these new variants are transmitted from parents to offspring, the mode of transmission is simple, complexity is achieved by the rare formation of new genes by chromosome duplication, biologic evolution occurs with all forms of life, and the biology of humans requires cultural evolution. See Cultural evolution. (12 Dec 1998) |
| chemical evolution | The theory of the process by which life arose from inorganic matter. (05 Mar 2000) |
| coincidental evolution | <molecular biology> The tendency for the same mutation to arise simultaneously in all copies of a gene which has been duplicated. (09 Oct 1997) |
| concerted evolution | The ability of two related genes to evolve together as though constituting a single locus. Synonym: coincidental evolution. (05 Mar 2000) |
| convergent evolution | The process where two unrelated structures in unrelated organisms evolve to perform similar functions. (The structures are called analogous structures.) For example: the wings of bats, birds, and insects evolved separately from each other but all are used to perform the function of flying. For another example: the complex eyes of vertebrates, cephalopods (squid and octopus), cubozoan jellyfish, and arthropods (insects, spiders, crustaceans) evolved separately, but all perform the function of vision. (09 Oct 1997) |
| cultural evolution | The continuous developmental process of a culture from simple to complex forms and from homogeneous to heterogeneous qualities. (12 Dec 1998) |
| saltatory evolution | The theory that evolution 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. Compare: emergent evolution. (05 Mar 2000) |
| spontaneous evolution | The unaided delivery of the foetus from a transverse lie. (05 Mar 2000) |
| Denman's spontaneous evolution | A mechanism of spontaneous molding of the foetus 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. (05 Mar 2000) |
| directed molecular evolution | Techniques used to produce molecules exhibiting properties that conform to the demands of the experimenter. (12 Dec 1998) |