Wednesday, October 29, 2014

Darwin was influenced by Charles Lyell's

Darwin was influenced by Charles Lyell's ideas of environmental change causing ecological shifts, leading to what Augustin de Candolle had called a war between competing plant species, competition well described by the botanist W. Herbert. Darwin was struck by Malthus's phrase "struggle for existence" used of warring human tribes.[66][67] Sony VAIO PCG-81312L battery Several writers anticipated evolutionary aspects of Darwin's theory, and in the third edition of On the Origin of Species published in 1861 Darwin named those he knew about in an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species, which he expanded in later editions.[68] In 1813, William Charles Wells read before the Royal Society essays assuming that there had been evolution of humans, and recognising the principle of natural selection. Sony VAIO PCG-8131L battery Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in 1858, but Darwin later acknowledged that Wells had recognised the principle before them, writing that the paper "An Account of a White Female, part of whose Skin resembles that of a Negro" was published in 1818, and "he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; Sony VAIO PCG-8141L battery but he applies it only to the races of man, and to certain characters alone."[69] Patrick Matthew wrote in the obscure book Naval Timber & Arboriculture (1831) of "continual balancing of life to circumstance. ... [The] progeny of the same parents, under great differences of circumstance, might, in several generations, even become distinct species, incapable of co-reproduction."[70] Sony VAIO PCG-8152L battery Charles Darwin discovered this work after the initial publication of the Origin. In the brief historical sketch that Darwin included in the 3rd edition he says "Unfortunately the view was given by Mr. Matthew very briefly in an Appendix to a work on a different subject ... He clearly saw, however, the full force of the principle of natural selection."[71] Sony VAIO PCG-8161L battery However, as historian of science Peter J. Bowler says, "Through a combination of bold theorizing and comprehensive evaluation, Darwin came up with a concept of evolution that was unique for the time." Bowler goes on to say that simple priority alone is not enough to secure a place in the history of science; someone has to develop an idea and convince others of its importance to have a real impact.[72Sony VAIO PCG-9131L battery ] T. H. Huxley said in his essay on the reception of the Origin of Species: The suggestion that new species may result from the selective action of external conditions upon the variations from their specific type which individuals present and which we call spontaneous because we are ignorant of their causation is as wholly unknown to the historian of scientific ideas as it was to biological specialists before 1858. But that suggestion is the central idea of the Origin of Species, and contains the quintessence ofDarwinism. Sony VAIO PCG-3E1M battery The biogeographical patterns Charles Darwin observed in places such as the Galapagos islands during the voyage of the Beaglecaused him to doubt the fixity of species, and in 1837 Darwin started the first of a series of secret notebooks ontransmutation. Darwin's observations led him to view transmutation as a process of divergence and branching, rather than the ladder-like progression envisioned by Lamarck and others. Sony VAIO PCG-9Z1L battery In 1838 he read the new 6th edition of An Essay on the Principle of Population, written in the late 18th century by Thomas Malthus. Malthus' idea of population growth leading to a struggle for survival combined with Darwin's knowledge on how breeders selected traits, led to the inception of Darwin's theory of natural selection. Darwin did not publish his ideas on evolution for 20 years. Sony VAIO PCG-7148L battery However he did share them with certain other naturalists and friends, starting with Joseph Hooker, with whom he discussed his unpublished 1844 essay on natural selection. During this period he used the time he could spare from his other scientific work to slowly refine his ideas and, aware of the intense controversy around transmutation, amass evidence to support them. Sony VAIO PCG-7151L battery In September 1854 he began full-time work on writing his book on natural selection.[63][74][75] Unlike Darwin, Alfred Russel Wallace, influenced by the book Vestiges of the Natural History of Creation, already suspected that transmutation of species occurred when he began his career as a naturalist. Sony VAIO PCG-7152L battery By 1855 his biogeographical observations during his field work in South America and the Malay Archipelago made him confident enough in a branching pattern of evolution to publish a paper stating that every species originated in close proximity to an already existing closely allied species. Like Darwin, it was Wallace's consideration of how the ideas of Malthus might apply to animal populations that led him to conclusions very similar to those reached by Darwin about the role of natural selection. Sony VAIO PCG-7153L battery In February 1858 Wallace, unaware of Darwin's unpublished ideas, composed his thoughts into an essay and mailed them to Darwin, asking for his opinion. The result was the joint publication in July of an extract from Darwin's 1844 essay along with Wallace's letter. Darwin also began work on a short abstract summarising his theory, which he would publish in 1859 as On the Origin of Species. Sony VAIO PCG-7154L battery By the 1850s, whether or not species evolved was a subject of intense debate, with prominent scientists arguing both sides of the issue.[77] The publication of Charles Darwin's On the Origin of Species (1859) fundamentally transformed the discussion over biological origins.[78] Darwin argued that his branching version of evolution explained a wealth of facts in biogeography, anatomy, embryology, and other fields of biology. Sony VAIO PCG-7161L battery He also provided the first cogent mechanism by which evolutionary change could persist: his theory ofnatural selection.One of the first and most important naturalists to be convinced by Origin of the reality of evolution was the British anatomist Thomas Henry Huxley. Huxley recognized that unlike the earlier transmutational ideas of Lamarck and Vestiges, Sony VAIO PCG-7162L battery Darwin's theory provided a mechanism for evolution without supernatural involvement, even if Huxley himself was not completely convinced that natural selection was the key evolutionary mechanism. Huxley would make advocacy of evolution a cornerstone of the program of the X Club to reform and professionalise science by displacing natural theology with naturalism and to end the domination of British natural science by the clergy. Sony VAIO PCG-7171L battery By the early 1870s in English-speaking countries, thanks partly to these efforts, evolution had become the mainstream scientific explanation for the origin of species.[79] In his campaign for public and scientific acceptance of Darwin's theory, Huxley made extensive use of new evidence for evolution from paleontology. Sony VAIO PCG-7172L battery This included evidence that birds had evolved from reptiles, including the discovery of Archaeopteryx in Europe, and a number of fossils of primitive birds with teeth found in North America. Another important line of evidence was the finding of fossils that helped trace the evolution of the horse from its small five-toed ancestors.[80] However, acceptance of evolution among scientists in non-Sony VAIO PCG-7173L battery English speaking nations such as France, and the countries of southern Europe and Latin America was slower. An exception to this was Germany, where both August Weismann and Ernst Haeckelchampioned this idea: Haeckel used evolution to challenge the established tradition of metaphysical idealism in German biology, much as Huxley used it to challenge natural theology in Britain.[81] Sony VAIO PCG-7174L battery Haeckel and other German scientists would take the lead in launching an ambitious programme to reconstruct the evolutionary history of life based on morphology and embryology.[82] Darwin's theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution.[83] Sony VAIO PCG-7181L battery However, this theory could not explain several critical components of the evolutionary process. Specifically, Darwin was unable to explain the source of variation in traits within a species, and could not identify a mechanism that could pass traits faithfully from one generation to the next. Darwin's hypothesis of pangenesis, while relying in part on the inheritance of acquired characteristics, Sony VAIO PCG-7182L battery proved to be useful for statistical models of evolution that were developed by his cousinFrancis Galton and the "biometric" school of evolutionary thought. However, this idea proved to be of little use to other biologists. Charles Darwin was aware of the severe reaction in some parts of the scientific community against the suggestion made inVestiges of the Natural History of Creation that humans had arisen from animals by a process of transmutation. Sony VAIO PCG-7183L battery Therefore he almost completely ignored the topic of human evolution in The Origin of Species. Despite this precaution, the issue featured prominently in the debate that followed the book's publication. For most of the first half of the 19th century, the scientific community believed that, although geology had shown that the Earth and life were very old, human beings had appeared suddenly just a few thousand years before the present. Sony VAIO PCG-7184L battery However, a series of archaeological discoveries in the 1840s and 1850s showed stone tools associated with the remains of extinct animals. By the early 1860s, as summarized in Charles Lyell's 1863 bookGeological Evidences of the Antiquity of Man, it had become widely accepted that humans had existed during a prehistoric period – which stretched many thousands of years before the start of written history. Sony VAIO PCG-7185L battery This view of human history was more compatible with an evolutionary origin for humanity than was the older view. On the other hand, at that time there was no fossil evidence to demonstrate human evolution. The only human fossils found before the discovery of Java man in the 1890s were either of anatomically modern humans or of Neanderthals that were too close, Sony VAIO PCG-381L battery especially in the critical characteristic of cranial capacity, to modern humans for them to be convincing intermediates between humans and other primates.[86] Therefore the debate that immediately followed the publication of The Origin of Species centered on the similarities and differences between humans and modern apes. Sony VAIO PCG-382L battery Carolus Linnaeus had been criticised in the 18th century for grouping humans and apes together as primates in his ground breaking classification system.[87] Richard Owen vigorously defended the classification suggested by Cuvier and Johann Friedrich Blumenbach that placed humans in a separate order from any of the other mammals, which by the early 19th century had become the orthodox view. Sony VAIO PCG-383L battery On the other hand, Thomas Henry Huxley sought to demonstrate a close anatomical relationship between humans and apes. In one famous incident, which became known as the Great Hippocampus Question, Huxley showed that Owen was mistaken in claiming that the brains of gorillaslacked a structure present in human brains. Huxley summarized his argument in his highly influential 1863 book Evidence as to Man's Place in Nature. Sony VAIO PCG-384L battery Another viewpoint was advocated by Charles Lyell and Alfred Russel Wallace. They agreed that humans shared a common ancestor with apes, but questioned whether any purely materialistic mechanism could account for all the differences between humans and apes, especially some aspects of the human mind.[86] In 1871, Darwin published The Descent of Man, and Selection in Relation to Sex, which contained his views on human evolution. Sony VAIO PCG-391L battery Darwin argued that the differences between the human mind and the minds of the higher animals were a matter of degree rather than of kind. For example, he viewed morality as a natural outgrowth of instincts that were beneficial to animals living in social groups. He argued that all the differences between humans and apes were explained by a combination of the selective pressures that came from our ancestors moving from the trees to the plains, Sony VAIO PCG-393L battery and sexual selection. The debate over human origins, and over the degree of human uniqueness continued well into the 20th century. The concept of evolution was widely accepted in scientific circles within a few years of the publication of Origin, but the acceptance of natural selection as its driving mechanism was much less widespread. Sony VAIO PCG-394L battery The four major alternatives to natural selection in the late 19th century were theistic evolution, neo-Lamarckism, orthogenesis, and saltationism. Theistic evolution was the idea that God intervened in the process of evolution, to guide it in such a way that the living world could still be considered to be designed. The term was promoted by Darwin's greatest American advocate Asa Gray. Sony VAIO PCG-3A1L battery However, this idea gradually fell out of favor among scientists, as they became more and more committed to the idea of methodological naturalism and came to believe that direct appeals to supernatural involvement were scientifically unproductive. By 1900, theistic evolution had largely disappeared from professional scientific discussions, although it retained a strong popular following. Sony VAIO PCG-3A2L battery In the late 19th century, the term neo-Lamarckism came to be associated with the position of naturalists who viewed the inheritance of acquired characteristics as the most important evolutionary mechanism. Advocates of this position included the British writer and Darwin critic Samuel Butler, the German biologist Ernst Haeckel, and the American paleontologist Edward Drinker Cope. Sony VAIO PCG-3A3L battery They considered Lamarckism to be philosophically superior to Darwin's idea of selection acting on random variation. Cope looked for, and thought he found, patterns of linear progression in the fossil record. Inheritance of acquired characteristics was part of Haeckel'srecapitulation theory of evolution, which held that the embryological development of an organism repeats its evolutionary history.[88][89] Sony VAIO PCG-3A4L battery Critics of neo-Lamarckism, such as the German biologist August Weismann and Alfred Russel Wallace, pointed out that no one had ever produced solid evidence for the inheritance of acquired characteristics. Despite these criticisms, neo-Lamarckism remained the most popular alternative to natural selection at the end of the 19th century, and would remain the position of some naturalists well into the 20th century.[88][89] Sony VAIO PCG-41112L battery Orthogenesis was the hypothesis that life has an innate tendency to change, in a unilinear fashion, towards ever-greater perfection. It had a significant following in the 19th century, and its proponents included the Russian biologist Leo S. Berg and the American paleontologist Henry Fairfield Osborn. Orthogenesis was popular among some paleontologists, who believed that the fossil record showed a gradual and constant unidirectional change. Sony VAIO PCG-51211L battery Saltationism was the idea that new species arise as a result of large mutations. It was seen as a much faster alternative to the Darwinian concept of a gradual process of small random variations being acted on by natural selection, and was popular with early geneticists such as Hugo de Vries, William Bateson, and early in his career, T. H. Morgan. It became the basis of the mutation theory of evolution. Sony VAIO PCG-51311L battery The rediscovery of Gregor Mendel's laws of inheritance in 1900 ignited a fierce debate between two camps of biologists. In one camp were the Mendelians, who were focused on discrete variations and the laws of inheritance. They were led by William Bateson (who coined the word genetics) and Hugo de Vries (who coined the word mutation). Sony VAIO PCG-51312L battery Their opponents were the biometricians, who were interested in the continuous variation of characteristics within populations. Their leaders, Karl Pearson and Walter Frank Raphael Weldon, followed in the tradition of Francis Galton, who had focused on measurement and statistical analysis of variation within a population. The biometricians rejected Mendelian genetics on the basis that discrete units of heredity, Sony VAIO PCG-51411L battery such as genes, could not explain the continuous range of variation seen in real populations. Weldon's work with crabs and snails provided evidence that selection pressure from the environment could shift the range of variation in wild populations, but the Mendelians maintained that the variations measured by biometricians were too insignificant to account for the evolution of new species.[90][91] Sony VAIO PCG-51412L battery When T. H. Morgan began experimenting with breeding the fruit fly Drosophila melanogaster, he was a saltationist who hoped to demonstrate that a new species could be created in the lab by mutation alone. Instead, the work at his lab between 1910 and 1915 reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. Sony VAIO PCG-51511L battery His work also demonstrated that most mutations had relatively small effects, such as a change in eye color, and that rather than creating a new species in a single step, mutations served to increase variation within the existing population. The Mendelian and biometrician models were eventually reconciled with the development of population genetics. Sony VAIO PCG-51513L battery A key step was the work of the British biologist and statistician R.A. Fisher. In a series of papers starting in 1918 and culminating in his 1930 book The Genetical Theory of Natural Selection, Fisher showed that the continuous variation measured by the biometricians could be produced by the combined action of many discrete genes, and that natural selection could change gene frequencies in a population, resulting in evolution. Sony VAIO PCG-5N2L battery In a series of papers beginning in 1924, another British geneticist, J.B.S. Haldane, applied statistical analysis to real-world examples of natural selection, such as the evolution of industrial melanism in peppered moths, and showed that natural selection worked at an even faster rate than Fisher assumed.[92][93] Sony VAIO PCG-5N4L battery The American biologist Sewall Wright, who had a background in animal breeding experiments, focused on combinations of interacting genes, and the effects of inbreeding on small, relatively isolated populations that exhibited genetic drift. In 1932, Wright introduced the concept of an adaptive landscape and argued that genetic drift and inbreeding could drive a small, Sony VAIO PCG-5P2L battery isolated sub-population away from an adaptive peak, allowing natural selection to drive it towards different adaptive peaks. The work of Fisher, Haldane and Wright founded the discipline of population genetics. This integrated natural selection with Mendelian genetics, which was the critical first step in developing a unified theory of how evolution worked. Sony VAIO PCG-5P4L battery

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