- Evolution
- The continuing process of change, especially in reference to natural selection. Charles Darwin (1809-82) noted that successful species produce more offspring in each generation than are needed to replace the adults who die. Not all offspring survive. Some creatures or plants struggle to survive. Many things affect an individual's chances of survival, including its ability to obtain enough food and avoid being killed. Sometimes there are differences which may make it easier for an individual to survive long enough to reproduce. The species would thus have changed or evolved to favor traits that favor survival and reproduction. Darwin called this process "natural selection", as explained in his book "On the Origin of Species" in 1859.
* * *1. 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. 3. The liberation of a gas or heat in the course of a chemical or enzymatic reaction. [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. SYN: organic e..- coincidental e. SYN: concerted e..- concerted e. the ability of two related genes to evolve together as though constituting a single locus. SYN: 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.- divergent e. the process by which a species or gene product gives rise to two or more different products.- 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. SYN: 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..
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evo·lu·tion .ev-ə-'lü-shənalso .ē-və- n1) a process of change in a certain direction <tumor \evolution and progression (I. J. Fidler )(et al)>2 a) the historical development of a biological group (as a race or species): PHYLOGENYb) a theory that the various types of animals and plants have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generationsevo·lu·tion·ari·ly -shə-.ner-ə-lē advevo·lu·tion·ary -shə-.ner-ē adj* * *
evo·lu·tion (ev″ə-looґshən) [L. evolutio, from e out + volvere to roll] 1. an unrolling. 2. a process of development in which an organ or organism becomes more and more complex by the differentiation of its parts; a continuous and progressive change according to certain laws and by means of resident forces.
Medical dictionary. 2011.
