Natural Selection 2011 Subtitles WORK
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On the Origin of Species (or, more completely, On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life),[3] published on 24 November 1859, is a work of scientific literature by Charles Darwin that is considered to be the foundation of evolutionary biology.[4] Darwin's book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. The book presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution. Darwin included evidence that he had collected on the Beagle expedition in the 1830s and his subsequent findings from research, correspondence, and experimentation.[5]
The book was written for non-specialist readers and attracted widespread interest upon its publication. Darwin was already highly regarded as a scientist, so his findings were taken seriously and the evidence he presented generated scientific, philosophical, and religious discussion. The debate over the book contributed to the campaign by T. H. Huxley and his fellow members of the X Club to secularise science by promoting scientific naturalism. Within two decades, there was widespread scientific agreement that evolution, with a branching pattern of common descent, had occurred, but scientists were slow to give natural selection the significance that Darwin thought appropriate. During "the eclipse of Darwinism" from the 1880s to the 1930s, various other mechanisms of evolution were given more credit. With the development of the modern evolutionary synthesis in the 1930s and 1940s, Darwin's concept of evolutionary adaptation through natural selection became central to modern evolutionary theory, and it has now become the unifying concept of the life sciences.
Darwin now had the basic framework of his theory of natural selection, but he was fully occupied with his career as a geologist and held back from compiling it until his book on The Structure and Distribution of Coral Reefs was completed.[35][36] As he recalled in his autobiography, he had "at last got a theory by which to work", but it was only in June 1842 that he allowed himself "the satisfaction of writing a very brief abstract of my theory in pencil".[37]
Darwin's barnacle studies convinced him that variation arose constantly and not just in response to changed circumstances. In 1854, he completed the last part of his Beagle-related writing and began working full-time on evolution. He now realised that the branching pattern of evolutionary divergence was explained by natural selection working constantly to improve adaptation. His thinking changed from the view that species formed in isolated populations only, as on islands, to an emphasis on speciation without isolation; that is, he saw increasing specialisation within large stable populations as continuously exploiting new ecological niches. He conducted empirical research focusing on difficulties with his theory. He studied the developmental and anatomical differences between different breeds of many domestic animals, became actively involved in fancy pigeon breeding, and experimented (with the help of his son Francis) on ways that plant seeds and animals might disperse across oceans to colonise distant islands. By 1856, his theory was much more sophisticated, with a mass of supporting evidence.[44][46]
Darwin was hard at work on the manuscript for his "big book" on Natural Selection, when on 18 June 1858 he received a parcel from Wallace, who stayed on the Maluku Islands (Ternate and Gilolo). It enclosed twenty pages describing an evolutionary mechanism, a response to Darwin's recent encouragement, with a request to send it on to Lyell if Darwin thought it worthwhile. The mechanism was similar to Darwin's own theory.[52] Darwin wrote to Lyell that "your words have come true with a vengeance, ... forestalled" and he would "of course, at once write and offer to send [it] to any journal" that Wallace chose, adding that "all my originality, whatever it may amount to, will be smashed".[54] Lyell and Hooker agreed that a joint publication putting together Wallace's pages with extracts from Darwin's 1844 Essay and his 1857 letter to Gray should be presented at the Linnean Society, and on 1 July 1858, the papers entitled On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection, by Wallace and Darwin respectively, were read out but drew little reaction. While Darwin considered Wallace's idea to be identical to his concept of natural selection, historians have pointed out differences. Darwin described natural selection as being analogous to the artificial selection practised by animal breeders, and emphasised competition between individuals; Wallace drew no comparison to selective breeding, and focused on ecological pressures that kept different varieties adapted to local conditions.[55][56][57] Some historians have suggested that Wallace was actually discussing group selection rather than selection acting on individual variation.[58]
By mid-March 1859 Darwin's abstract had reached the stage where he was thinking of early publication; Lyell suggested the publisher John Murray, and met with him to find if he would be willing to publish. On 28 March Darwin wrote to Lyell asking about progress, and offering to give Murray assurances "that my Book is not more un-orthodox, than the subject makes inevitable." He enclosed a draft title sheet proposing An abstract of an Essay on the Origin of Species and Varieties Through natural selection, with the year shown as "1859".[64][65]
In January 1871, George Jackson Mivart's On the Genesis of Species listed detailed arguments against natural selection, and claimed it included false metaphysics.[89] Darwin made extensive revisions to the sixth edition of the Origin (this was the first edition in which he used the word "evolution" which had commonly been associated with embryological development, though all editions concluded with the word "evolved"[90][91]), and added a new chapter VII, Miscellaneous objections, to address Mivart's arguments.[2][92]
Starting with the third edition, Darwin prefaced the introduction with a sketch of the historical development of evolutionary ideas.[113] In that sketch he acknowledged that Patrick Matthew had, unknown to Wallace or himself, anticipated the concept of natural selection in an appendix to a book published in 1831;[114] in the fourth edition he mentioned that William Charles Wells had done so as early as 1813.[115]
In Chapter III, Darwin asks how varieties "which I have called incipient species" become distinct species, and in answer introduces the key concept he calls "natural selection";[123] in the fifth edition he adds, "But the expression often used by Mr. Herbert Spencer, of the Survival of the Fittest, is more accurate, and is sometimes equally convenient."[124]
Chapter IV details natural selection under the "infinitely complex and close-fitting ... mutual relations of all organic beings to each other and to their physical conditions of life".[126] Darwin takes as an example a country where a change in conditions led to extinction of some species, immigration of others and, where suitable variations occurred, descendants of some species became adapted to new conditions. He remarks that the artificial selection practised by animal breeders frequently produced sharp divergence in character between breeds, and suggests that natural selection might do the same, saying:
In Darwin's time there was no agreed-upon model of heredity;[131] in Chapter I Darwin admitted, "The laws governing inheritance are quite unknown."[132] He accepted a version of the inheritance of acquired characteristics (which after Darwin's death came to be called Lamarckism), and Chapter V discusses what he called the effects of use and disuse; he wrote that he thought "there can be little doubt that use in our domestic animals strengthens and enlarges certain parts, and disuse diminishes them; and that such modifications are inherited", and that this also applied in nature.[133] Darwin stated that some changes that were commonly attributed to use and disuse, such as the loss of functional wings in some island-dwelling insects, might be produced by natural selection. In later editions of Origin, Darwin expanded the role attributed to the inheritance of acquired characteristics. Darwin also admitted ignorance of the source of inheritable variations, but speculated they might be produced by environmental factors.[134][135] However, one thing was clear: whatever the exact nature and causes of new variations, Darwin knew from observation and experiment that breeders were able to select such variations and produce huge differences in many generations of selection.[119] The observation that selection works in domestic animals is not destroyed by lack of understanding of the underlying hereditary mechanism.
Breeding of animals and plants showed related varieties varying in similar ways, or tending to revert to an ancestral form, and similar patterns of variation in distinct species were explained by Darwin as demonstrating common descent. He recounted how Lord Morton's mare apparently demonstrated telegony, offspring inheriting characteristics of a previous mate of the female parent, and accepted this process as increasing the variation available for natural selection.[136][137]
Another difficulty, related to the first one, is the absence or rarity of transitional varieties in time. Darwin commented that by the theory of natural selection "innumerable transitional forms must have existed," and wondered "why do we not find them embedded in countless numbers in the crust of the earth?"[144] (For further discussion of these difficulties, see Speciation#Darwin's dilemma: Why do species exist? and Bernstein et al.[145] and Michod.[146]) 2b1af7f3a8