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Natural Selection, Natural Selection

In other words, natural selection is an important process (though not the only process) by which evolution takes place within a population of organisms.

The term was introduced by Darwin in his groundbreaking 1859 book On the Origin of Species , Darwin C (1859) On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life John Murray, London; modern reprint Published online at The complete work of Charles Darwin online : On the origin of species by means of natural selection, or the preservation of favoured races in the struggle for life.

The concept of natural selection was originally developed in the absence of a valid theory of heredity; at the time of Darwin's writing, nothing was known of modern genetics.

Natural selection remains the primary explanation for adaptive evolution.

In modern times, it is understood that selection acts on an organism's phenotype, or observable characteristics, but it is the organism's genetic make-up or genotype which is inherited. The phenotype is the result of the genotype and the environment in which the organism lives (see Genotype-phenotype distinction). This is the link between natural selection and genetics, as described in the modern evolutionary synthesis. Although a complete theory of evolution also requires an account of how genetic variation arises in the first place (such as by mutation and sexual reproduction) and includes other evolutionary mechanisms (such as gene flow), natural selection is still understood as a fundamental mechanism for evolution.

However, natural selection is "blind" in the sense that changes in phenotype (physical and behavioral characteristics) can give a reproductive advantage regardless of whether or not the trait is heritable (non heritable traits can be the result of environmental factors or the life experience of the organism).

Fisher RA (1930) The Genetical Theory of Natural Selection Clarendon Press, Oxford Works employing or describing this usage: It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects; when this distinction is important, scientists define "natural selection" specifically as "those mechanisms that contribute to the selection of individuals that reproduce", without regard to whether the basis of the selection is heritable. This is sometimes referred to as "phenotypic natural selection". Works employing or describing this usage: Lande R & Arnold SJ (1983) The measurement of selection on correlated characters.

Broadly, individuals which are more "fit" have better potential for survival, as in the well-known phrase "survival of the fittest". However, as with natural selection above, the precise meaning of the term is much more subtle, and Richard Dawkins manages in his later books to avoid it entirely. (He devotes a chapter of his book, The Extended Phenotype , to discussing the various senses in which the term is used). Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes will become more common in the adult population of the next generation.

Since the discovery of penicillin in 1928 by Alexander Fleming, antibiotics have been used to fight bacterial diseases. Natural populations of bacteria contain, among their vast numbers of individual members, considerable variation in their genetic material, primarily as the result of mutations. When exposed to antibiotics, most bacteria die quickly, but some may have mutations that make them slightly less susceptible. If the exposure to antibiotics is short, these individuals will survive the treatment. This selective elimination of maladapted individuals from a population is natural selection.

In the absence of natural selection to preserve such a trait, it will become more variable and deteriorate over time, possibly resulting in a vestigial manifestation of the trait. In many circumstances, the apparently vestigial structure may retain a limited functionality, or may be co-opted for other advantageous traits in a phenomenon known as preadaptation. A famous example of a vestigial structure, the eye of the blind mole rat, is believed to retain function in photoperiod perception. Sanyal S, Jansen HG, de Grip WJ, Nevo E, de Jong WW. (1990). The eye of the blind mole rat, Spalax ehrenbergi. Rudiment with hidden function.

Conway Zirkle (1941). Natural Selection before the "Origin of Species", Proceedings of the American Philosophical Society 84 (1), p. 71-123.

After the publication of The Origin of Species , educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its "unguided" and non-progressive nature, Eisley L. (1958).

Although Austrian monk Gregor Mendel, the father of modern genetics, was a contemporary of Darwin's, his work would lie in obscurity until the early 20th century. Only after the integration of Darwin's theory of evolution with a complex statistical appreciation of Gregor Mendel's 're-discovered' laws of inheritance did natural selection become generally accepted by scientists. The work of Ronald Fisher (who developed the required mathematical language and the genetical theory of natural selection), J.B.S. Haldane (who introduced the concept of the "cost" of natural selection), Haldane JBS (1932) The Causes of Evolution ; Haldane JBS (1957) The cost of natural selection.

This claim inspired some of Darwin's most ardent supporters—and provoked the most profound opposition. The radicalism of natural selection, according to Stephen Jay Gould, The New York Review of Books: Darwinian Fundamentalism (accessed May 6, 2006) lay in its power to "dethrone some of the deepest and most traditional comforts of Western thought". In particular, it challenged long-standing beliefs in such concepts as a special and exalted place for humans in the natural world and a benevolent creator whose intentions were reflected in nature's order and design.

Engels F (1873-86) Dialectics of Nature 3d ed. Moscow: Progress, 1964 [8] Interpretation of natural selection as necessarily 'progressive', leading to increasing 'advances' in intelligence and civilisation, was used as a justification for colonialism and policies of eugenics, as well as broader sociopolitical positions now described as Social Darwinism. Konrad Lorenz won the Nobel Prize in Physiology or Medicine in 1973 for his analysis of animal behavior in terms of the role of natural selection (particularly group selection). However, in Germany in 1940, in writings that he subsequently disowned, he used the theory as a justification for policies of the Nazi state. He wrote "... selection for toughness, heroism, and social utility...must be accomplished by some human institution, if mankind, in default of selective factors, is not to be ruined by domestication-induced degeneracy. The racial idea as the basis of our state has already accomplished much in this respect." Quoted in translation in Eisenberg L (2005) Which image for Lorenz.

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