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Coloration evidence for natural selection InCharles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation.
He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved". As long as there is some variation between them and that variation is heritablethere will be an inevitable selection of individuals with the most advantageous variations.
If the variations are heritable, then differential reproductive success leads to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species.
It struck him that as population outgrew resources, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species.
If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man.
But if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised.
This principle of preservation, I have called, for the sake of brevity, Natural Selection. He was in the process of writing his "big book" to present his research when the naturalist Alfred Russel Wallace independently conceived of the principle and described it in an essay he sent to Darwin to forward to Charles Lyell.
Lyell and Joseph Dalton Hooker decided to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection was read to the Linnean Society of London announcing co-discovery of the principle in July In the 3rd edition of Darwin acknowledged that others—like William Charles Wells inand Patrick Matthew in —had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications.
Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called " artificial selection "; in his early manuscripts he referred to a "Nature" which would do the selection.
At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: After the publication of On 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,  a response that has been characterised as the single most significant impediment to the idea's acceptance.
Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient. Modern synthesis 20th century Natural selection relies crucially on the idea of heredity, but developed before the basic concepts of genetics.
Although the Moravian monk Gregor Mendelthe father of modern genetics, was a contemporary of Darwin's, his work lay in obscurity, only being rediscovered in Haldane introduced the concept of the "cost" of natural selection.
Hamilton conceived of kin selection in A second synthesis was brought about at the end of the 20th century by advances in molecular geneticscreating the field of evolutionary developmental biology "evo-devo"which seeks to explain the evolution of form in terms of the genetic regulatory programs which control the development of the embryo at molecular level.
Natural selection is here understood to act on embryonic development to change the morphology of the adult body.CBSE Class 11 English Passages for Note Making and Summarizing Prepared as per NCERT Books Prepared by Passionate Teachers to Improve Analytical Skills.
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