<P> Once he had his theory, Darwin was meticulous about gathering and refining evidence before making his idea public . 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 Lyell and Joseph Dalton Hooker decided to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by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 1858 . Darwin published a detailed account of his evidence and conclusions in On the Origin of Species in 1859 . In the 3rd edition of 1861 Darwin acknowledged that others--like William Charles Wells in 1813, and Patrick Matthew in 1831--had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications . </P> <P> 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: "I am convinced that Natural Selection has been the main but not exclusive means of modification ." In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term "Natural Selection", preferring the term "Natural Preservation". </P> <P> For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection . 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 . However, some thinkers enthusiastically embraced natural selection; after reading Darwin, Herbert Spencer introduced the phrase survival of the fittest, which became a popular summary of the theory . The fifth edition of On the Origin of Species published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: "But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient ." Although the phrase is still often used by non-biologists, modern biologists avoid it because it is tautological if "fittest" is read to mean "functionally superior" and is applied to individuals rather than considered as an averaged quantity over populations . </P> <P> Natural selection relies crucially on the idea of heredity, but developed before the basic concepts of genetics . Although the Moravian monk Gregor Mendel, the father of modern genetics, was a contemporary of Darwin's, his work lay in obscurity, only being rediscovered in 1900 . With the early 20th century integration of evolution with Mendel's laws of inheritance, the so - called modern synthesis, scientists generally came to accept natural selection . The synthesis grew from advances in different fields . Ronald Fisher developed the required mathematical language and wrote The Genetical Theory of Natural Selection (1930). J.B.S. Haldane introduced the concept of the "cost" of natural selection . Sewall Wright elucidated the nature of selection and adaptation . In his book Genetics and the Origin of Species (1937), Theodosius Dobzhansky established the idea that mutation, once seen as a rival to selection, actually supplied the raw material for natural selection by creating genetic diversity . </P>

Where does all the natural variation necessary for natural selection come from