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"survival of the fittest," the principle that in nature those individuals best able to adapt to their environment will survive and reproduce, whereas those less able will die without progeny, and the genes carried by the survivors will increase in frequency. This principle is heuristic rather than rigorous because it cannot be tested, the outcome being tautologous with the empiric definition of fitness.
The process in nature by which, according to Darwin's theory of evolution, organisms that are better adapted to their environment tend to survive longer and transmit more of their genetic characteristics to succeeding generations than do those that are less well adapted.
the natural evolutionary processes by which the organisms that are best adapted to an environment tend to survive and propagate whereas those that are unfit are less likely to do so. Compare artificial selection.
natural selectionA general term for a shift in the frequency of a gene’s allelic variants within a population over time, which reflects the differential reproductive success of individual genotypes.
nat·u·ral se·lec·tion(nă-chŭr'ăl sĕ-lek'shŭn)
Colloquially, "survival of the fittest," the principle that in nature those individuals best able to adapt to their environment will survive and reproduce, whereas those less able will die without progeny, and the genes carried by the survivors will increase in frequency. This principle is heuristic rather than rigorous because it cannot be tested, the outcome being tautologous with the empiric definition of fitness.
natural selectionThe Darwin-originated principle that individuals of a species happening, by normal genetic rearrangement or by mutation, to possess inherited characteristics with survival value relative to a particular environment are more likely to survive long enough to reproduce and increase the numbers having these characteristics. Natural selection occurs quickly in rapidly reproducing micro-organisms. (Charles Darwin, 1809–82, English naturalist).
natural selectionthe mechanism, proposed by Charles DARWIN, by which gradual evolutionary changes take place. Organisms which are better adapted to the environment in which they live produce more viable young, so increasing their proportion in the population; thus particular characteristics are ‘selected’ and others are lost. Such a mechanism depends on the variability of individuals within the population. Such variability arises through MUTATION and other genetic events, the beneficial variants being preserved by NATURAL SELECTION.
occurs in nature, without the intervention of humans.
occur by chance when all variables for a population are constant except one, which is different for one large part of the population compared with the other, e.g. when half of a flock comes from one climate and the other half is a local resident in another climate.
the ecology that is best suited to a biological system, e.g. an individual insect-borne disease; the area in which the disease naturally flourishes best; an ecological niche.
history of a process or organism as it occurs in nature, e.g. course of a disease from infection to resolution.
natural killer (NK) cell
see natural killer cell.
selection occurring in nature, without any human intervention, direct or indirect.
ventilation without the use of artificially induced energy and the machines which it drives; the forces used are wind and the exchange of heat from within the barn and the external air, controlled by ventilation devices in the walls and the ceiling.