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On the Origin of Species, published on 24 November 1859, is a work of scientific literature by Charles Darwin which is considered to be the foundation of evolutionary biology. Its full title was On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for LifeHP Pavilion dv7-4150ec CPU Fan

For the sixth edition of 1872, the short title was changed to The Origin of Species. Darwin's book introduced the scientific theory that populations evolve over the course of generations through a process of natural selection. It presented a body of evidence that the diversity of life arose by common descent through a branching pattern of evolution. HP Pavilion dv5-1102tu CPU Fan

Darwin included evidence that he had gathered on the Beagle expedition in the 1830s and his subsequent findings from research, correspondence, and experimentation.

Various evolutionary ideas had already been proposed to explain new findings in biology. There was growing support for such ideas among dissident anatomists and the general public, SONY VGN-SZ220 CPU Fan

but during the first half of the 19th century the English scientific establishment was closely tied to the Church of England, while science was part of natural theology. Ideas about the transmutation of species were controversial as they conflicted with the beliefs that species were unchanging parts of a designed hierarchy and that humans were unique, unrelated to other animals. HP Pavilion dv7-6011tx CPU Fan

The political and theological implications were intensely debated, but transmutation was not accepted by the scientific mainstream.

The book was written for non-specialist readers and attracted widespread interest upon its publication. As Darwin was an eminent scientist, his findings were taken seriously and the evidence he presented generated scientific, philosophical, and religious discussion. HP Pavilion dv5-1040eb CPU Fan

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. ASUS F3Jv CPU Fan

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, now the unifying concept of the life sciences. IBM ThinkPad R50p 2887 CPU Fan

Darwin's theory of evolution is based on key facts and the inferences drawn from them, which biologist Ernst Mayr summarised as follows:

  • Every species is fertile enough that if all offspring survived to reproduce the population would grow (fact).

Despite periodic fluctuations, populations remain roughly the same size (fact). SONY VGN-CS36GJ/R CPU Fan

  • Resources such as food are limited and are relatively stable over time (fact).
  • A struggle for survival ensues (inference).
  • Individuals in a population vary significantly from one another (fact).

Much of this variation is inheritable (fact). Toshiba Satellite A215-S4807 CPU Fan

  • Individuals less suited to the environment are less likely to survive and less likely to reproduce; individuals more suited to the environment are more likely to survive and more likely to reproduce and leave their inheritable traits to future generations, which produces the process of natural selection (inference).

This slowly effected process results in populations changing to adapt to their environments, and ultimately, Toshiba Satellite Pro M10-SP405 CPU Fan

  • these variations accumulate over time to form new species (inference).

In later editions of the book, Darwin traced evolutionary ideas as far back as Aristotle;[4] the text he cites is a summary by Aristotle of the ideas of the earlier Greek philosopher Empedocles.[5] Early Christian Church Fathers and Medieval European scholars interpreted the Genesis creation narrative allegorically rather than as a literal historical account;[6HP Pavilion dv4-1120us CPU Fan

]organisms were described by their mythological and heraldic significance as well as by their physical form. Nature was widely believed to be unstable and capricious, with monstrous births from union between species, and spontaneous generation of life.

The Protestant Reformation inspired a literal interpretation of the Bible, Compaq Presario C550EM CPU Fan

with concepts of creation that conflicted with the findings of an emerging science seeking explanations congruent with the mechanical philosophy of René Descartes and theempiricism of the Baconian method. After the turmoil of the English Civil War, the Royal Society wanted to show that science did not threaten religious and political stability. John Ray developed an influential natural theology of rational order; Toshiba Qosmio E15-AV101 CPU Fan

in his taxonomy, species were static and fixed, their adaptation and complexity designed by God, and varieties showed minor differences caused by local conditions. In God's benevolent design, carnivores caused mercifully swift death, but the suffering caused by parasitism was a puzzling problem. The biological classification introduced by Carolus Linnaeus in 1735 also viewed species as fixed according to the divine plan. Toshiba Satellite L645D-S4056 CPU Fan

In 1766, Georges Buffon suggested that some similar species, such as horses and asses, or lions, tigers, and leopards, might be varieties descended from a common ancestor. The Ussher chronology of the 1650s had calculated creation at 4004 BC, but by the 1780s geologists assumed a much older world.Wernerians thought strata were deposits from shrinking seas, but James Hutton proposed a self-maintaining infinite cycle, anticipating uniformitarianism.[8] Toshiba Satellite A305-S6837 CPU Fan

Charles Darwin's grandfather Erasmus Darwin outlined a hypothesis of transmutation of species in the 1790s, and Jean-Baptiste Lamarck published a more developed theory in 1809. Both envisaged that spontaneous generation produced simple forms of life that progressively developed greater complexity, adapting to the environment by inheriting changes in adults caused by use or disuse. HP Pavilion dv7-4087cl CPU Fan

This process was later called Lamarckism. Lamarck thought there was an inherent progressive tendency driving organisms continuously towards greater complexity, in parallel but separate lineages with no extinction.[9] Geoffroycontended that embryonic development recapitulated transformations of organisms in past eras when the environment acted on embryos,HP Pavilion dv5-1118es CPU Fan

and that animal structures were determined by a constant plan as demonstrated by homologies. Georges Cuvier strongly disputed such ideas, holding that unrelated, fixed species showed similarities that reflected a design for functional needs.[10] His palæontological work in the 1790s had established the reality of extinction, which he explained by localcatastrophes, followed by repopulation of the affected areas by other species.[11] Toshiba Satellite A665-S6050 CPU Fan

In Britain, William Paley's Natural Theology saw adaptation as evidence of beneficial "design" by the Creator acting through natural laws. All naturalists in English universities were Church of England clergymen, and science became a search for these laws.[12] Geologists adapted catastrophism to show repeated worldwide annihilation and creation of new fixed species adapted to a changed environment, HP Pavilion G72-259WM CPU Fan

initially identifying the most recent catastrophe as the biblical flood.[13] Some anatomists such as Robert Grant were influenced by Lamarck and Geoffroy, but most naturalists regarded their ideas of transmutation as a threat to divinely appointed social order.

Darwin went to Edinburgh University in 1825 to study medicine. HP Pavilion dv6-3109ca  CPU  Fan

In his second year he neglected his medical studies for natural history and spent four months assisting Robert Grant's research into marine invertebrates. Grant revealed his enthusiasm for the transmutation of species, but Darwin rejected it.[15] AtCambridge University starting in 1827, Darwin learnt science as natural theology from botanist John Stevens Henslow, and read Paley, John Herschel and Alexander von Humboldt. HP Pavilion dv6782eg CPU Fan

Filled with zeal for science, he studied catastrophist geology with Adam Sedgwick.

In December 1831, he joined the Beagle expedition as a geologist and naturalist. He read Charles Lyell's Principles of Geology and from the first stop ashore, at St. Jago, found Lyell's uniformitarianism a key to the geological history of landscapes. SONY UDQF2PH52CF0 CPU Fan

Darwin discovered fossils resembling huge armadillos, and noted the geographical distribution of modern species in hope of finding their "centre of creation".[18] The three Fuegian missionaries the expedition returned to Tierra del Fuegowere friendly and civilised, yet to Darwin their relatives on the island seemed "miserable, degraded savages",[19] and he no longer saw an unbridgeable gap between humans and animals.[20] Toshiba UDQFRPH33CCM CPU Fan

As the Beagle neared England in 1836, he noted that species might not be fixed.[21][22]

Richard Owen showed that fossils of extinct species Darwin found in South America were allied to living species on the same continent. In March 1837, ornithologist John Gould announced that Darwin's Rhea was a separate species from the previously described rhea (though their territories overlapped), Toshiba Satellite A505-S6980 CPU Fan 

that mockingbirds collected on the Galápagos Islands represented three separate species each unique to a particular island, and that several distinct birds from those islands were all classified as finches.[23] Darwin began speculating, in a series of notebooks, on the possibility that "one species does change into another" to explain these findings, and around July sketched a genealogical branching of a single evolutionary tree, discarding Lamarck's independent lineages progressing to higher formsHP Pavilion dv7-2025es CPU Fan

Unconventionally, Darwin asked questions offancy pigeon and animal breeders as well as established scientists. At the zoo he had his first sight of an ape, and was profoundly impressed by how human the orangutan seemed.[27]

In late September 1838, he started reading Thomas Malthus's An Essay on the Principle of Population with its statistical argument that human populations, if unrestrained, TOSHIBA Satellite L300 CPU Fan

breed beyond their means and struggle to survive. Darwin related this to the struggle for existence among wildlife and botanist de Candolle's "warring of the species" in plants; he immediately envisioned "a force like a hundred thousand wedges" pushing well-adapted variations into "gaps in the economy of nature", so that the survivors would pass on their form and abilities, and unfavourable variations would be destroyed.[ HP G62-a10EJ CPU Fan

By December 1838, he had noted a similarity between the act of breeders selecting traits and a Malthusian Nature selecting among variants thrown up by "chance" so that "every part of newly acquired structure is fully practical and perfected".[31]

Darwin now had the framework of his theory of natural selection "by which to work",[32] Dell MF60100V1-Q000-G99 CPU Fan

but he was fully occupied with his career as a geologist and held off writing a sketch of his theory until his book on The Structure and Distribution of Coral Reefs was completed in May 1842.

Darwin continued to research and extensively revise his theory while focusing on his main work of publishing the scientific results of the Beagle voyage.[33] DELL R859C CPU Fan

He tentatively wrote of his ideas to Lyell in January 1842;[35] then in June he roughed out a 35-page "Pencil Sketch" of his theory.[36] Darwin began correspondence about his theorising with the botanist Joseph Dalton Hooker in January 1844, and by July had rounded out his "sketch" into a 230-page "Essay", to be expanded with his research results and published if he died prematurely.Toshiba Satellite A105-S2101 CPU Fan

In November 1844, the anonymously published popular science book Vestiges of the Natural History of Creation, written by Scottish journalist Robert Chambers, widened public interest in the concept of transmutation of species. Vestiges used evidence from the fossil record and embryology to support the claim that living things had progressed from the simple to the more complex over time. SONY Vaio VGN-FW140E CPU Fan

But it proposed a linear progression rather than the branching common descent theory behind Darwin's work in progress, and it ignored adaptation. Darwin read it soon after publication, and scorned its amateurish geology and zoology,[38] but he carefully reviewed his own arguments after leading scientists, including Adam Sedgwick, attacked its morality and scientific errors.[39] ACER Aspire 5730Z CPU Fan

Vestiges had significant influence on public opinion, and the intense debate helped to pave the way for the acceptance of the more scientifically sophisticated Origin by moving evolutionary speculation into the mainstream. While few naturalists were willing to consider transmutation, Herbert Spencer became an active proponent of Lamarckism and progressive development in the 1850s.[40] SONY Vaio VPC-EB4S1E/WI CPU Fan

Hooker was persuaded to take away a copy of the "Essay" in January 1847, and eventually sent a page of notes giving Darwin much needed feedback. Reminded of his lack of expertise in taxonomy, Darwin began an eight-year study of barnacles, becoming the leading expert on their classification. Using his theory, he discovered homologies showing that slightly changed body parts served different functions to meet new conditions, and he found an intermediate stage in the evolution of distinct sexes.[41][42]HP Pavilion dv9580ed CPU Fan

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. His thinking changed from the view that species formed in isolated populations only, as on islands, to an emphasis on speciation without isolation;Toshiba Satellite L305D-S5934 CPU Fan

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, SONY Vaio VGN-CR31S/P CPU Fan

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.

An 1855 paper on the "introduction" of species, written by Alfred Russel Wallace, claimed that patterns in the geographical distribution of living and fossil species could be explained if every new species always came into existence near an already existing, closely related species.[44] HP Pavilion dv5-1210et CPU Fan

Charles Lyell recognised the implications of Wallace's paper and its possible connection to Darwin's work, although Darwin did not, and in the spring of 1856 Lyell urged Darwin to publish his theory to establish priority. Darwin was torn between the desire to set out a full and convincing account and the pressure to quickly produce a short paper. SONY Vaio VGN-FW465J/B CPU Fan

He decided he did not want to expose his ideas to review by an editor as would have been required to publish in an academic journal. On 14 May 1856, he began a "sketch" account, and by July had decided to produce a full technical treatise on species.[45]

Darwin was hard at work on 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). HP Envy 15 CPU Fan

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.[45] Darwin wrote to Lyell that "your words have come true with a vengeance, ... forestalled" and he would "of course, HP Pavilion dv7-1190er CPU Fan

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".[46] Lyell and Hooker agreed that a joint paper 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 SelectionToshiba Satellite A105-S4074 CPU Fan

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;  IBM MCF-208AM05-1 CPU Fan

Wallace drew no comparison to selective breeding, and focused on ecological pressures that kept different varieties adapted to local conditions.

After the meeting, Darwin decided to write "an abstract of my whole work".[50] He started work on 20 July 1858, while on holiday atSandown,[51] and wrote parts of it from memory.[52] IBM MCF-217PAM05 CPU Fan

Lyell discussed arrangements with publisher John Murray III, of the publishing house John Murray,[53] who responded immediately to Darwin's letter of 31 March 1859[54] with an agreement to publish the book without even seeing the manuscript, and an offer to Darwin of 2⁄3 of the profits.[55] (eventually Murray paid £180 to Darwin for the 1st edition and by Darwin's death in 1882 the book was in its 6th edition, earning Darwin nearly £3000.[56]  HP GB0507PGV1-A CPU Fan

) Darwin had initially decided to call it An abstract of an Essay on the Origin of Species and Varieties Through natural selection, but with Murray's persuasion it was eventually changed to the snappier title: On the Origin of Species, with the title page adding by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life.[1] IBM MCF-217PAM05 CPU Fan

 Here the term "races" is used as an alternative for "varieties"and does not carry the modern connotation of human races—the first use in the book refers to "the several races, for instance, of the cabbage" and proceeds to a discussion of "the hereditary varieties or races of our domestic animals and plants".

Darwin had his basic theory of natural selection "by which to work" by December 1838, yet almost twenty years later, HP Pavilion dv6-3385la CPU Fan

when Wallace's letter arrived on 18 June 1858, Darwin was still not ready to publish his theory. It was long thought that Darwin avoided or delayed making his ideas public for personal reasons. Reasons suggested have included fear of religious persecution or social disgrace if his views were revealed, and concern about upsetting his clergymen naturalist friends or his pious wife Emma.HP Pavilion tx2510us  CPU  Fan

 Charles Darwin's illness caused repeated delays. His paper on Glen Roy had proved embarrassingly wrong, and he may have wanted to be sure he was correct. David Quammen has suggested all these factors may have contributed, and notes Darwin's large output of books and busy family life during that time.[58]

A more recent study by science historian John van Wyhe has determined that the idea that Darwin delayed publication only dates back to the 1940s, HP G62-b55EV CPU Fan

and Darwin's contemporaries thought the time he took was reasonable. Darwin always finished one book before starting another. While he was researching, he told many people about his interest in transmutation without causing outrage. He firmly intended to publish, but it was not until September 1854 that he could work on it full-time. His estimate that writing his "big book" would take five years was optimistic. HP Pavilion dv6-2145sf CPU Fan

On the Origin of Species was first published on Thursday 24 November 1859, priced at fifteen shillings. The book had been offered to booksellers at Murray's autumn sale on Tuesday 22 November, and all available copies had been taken up immediately. In total, 1,250 copies were printed but after deducting presentation and review copies, and five for Stationers' Hall copyright, around 1,170 copies were available for sale.[1] HP Pavilion dv7-1120ew CPU Fan

Significantly, 500 were taken by Mudie's Library, ensuring that the book promptly reached a large number of subscribers to the library.[60] The second edition of 3,000 copies was quickly brought out on 7 January 1860,[61] and incorporated numerous corrections as well as a response to religious objections by the addition of a new epigraph on page ii, a quotation fromCharles Kingsley, and the phrase "by the Creator" amended to the closing sentence.[62] HP 538340-001 CPU Fan

During Darwin's lifetime the book went through six editions, with cumulative changes and revisions to deal with counter-arguments raised. The third edition came out in 1861, with a number of sentences rewritten or added and an introductory appendix, An Historical Sketch of the Recent Progress of Opinion on the Origin of Species,[63] while the fourth in 1866 had further revisions. HP 535766-001 CPU Fan

The fifth edition, published on 10 February 1869, incorporated more changes and for the first time included the phrase "survival of the fittest", which had been coined by the philosopher Herbert Spencer in his Principles of Biology (1864).[64]

In January 1871, George Jackson Mivart's On the Genesis of Species listed detailed arguments against natural selection, and claimed it included falsemetaphysics.[65] HP 535442-001 CPU Fan

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"[66][67]), and added a new chapter VII,Miscellaneous objections, to address Mivart's arguments.[68][69] HP 535441-001 CPU Fan

The sixth edition was published by Murray on 19 February 1872 with "On" dropped from the title. Darwin had told Murray of working men in Lancashire clubbing together to buy the 5th edition at fifteen shillings and wanted it made more widely available; the price was halved to 7s 6d by printing in a smaller font. It includes a glossary compiled by W.S. Dallas. Book sales increased from 60 to 250 per month. HP 535439-001 CPU Fan

In the United States, Asa Gray negotiated with a Boston publisher for publication of an authorised American version, but learnt that two New York publishing firms were already planning to exploit the absence of international copyright to printOrigin.[70] Darwin was delighted by the popularity of the book, and asked Gray to keep any profits.[71] HP 535438-001 CPU Fan

Gray managed to negotiate a 5% royalty with Appleton's of New York,[72] who got their edition out in mid January 1860, and the other two withdrew. In a May letter, Darwin mentioned a print run of 2,500 copies, but it is not clear if this referred to the first printing only as there were four that year.[1][73]

The book was widely translated in Darwin's lifetime, but problems arose with translating concepts and metaphors, and some translations were biased by the translator's own agenda.[74] HP 533736-001 CPU Fan

Darwin distributed presentation copies in France and Germany, hoping that suitable applicants would come forward, as translators were expected to make their own arrangements with a local publisher. He welcomed the distinguished elderly naturalist and geologist Heinrich Georg Bronn, but the German translation published in 1860 imposed Bronn's own ideas, adding controversial themes that Darwin had deliberately omitted. IBM 13R2760 CPU Fan

Bronn translated "favoured races" as "perfected races", and added essays on issues including the origin of life, as well as a final chapter on religious implications partly inspired by Bronn's adherence to Naturphilosophie.[75] In 1862, Bronn produced a second edition based on the third English edition and Darwin's suggested additions, but then died of a heart attack.[76] ACER LU.S040A.067 CPU Fan

Darwin corresponded closely with Julius Victor Carus, who published an improved translation in 1867.[77] Darwin's attempts to find a translator in France fell through, and the translation by Clémence Royer published in 1862 added an introduction praising Darwin's ideas as an alternative to religious revelation and promoting ideas anticipating social Darwinism and eugenics, ACER LU.S050B.078 CPU Fan

as well as numerous explanatory notes giving her own answers to doubts that Darwin expressed. Darwin corresponded with Royer about a second edition published in 1866 and a third in 1870, but he had difficulty getting her to remove her notes and was troubled by these editions.[76][78] He remained unsatisfied until a translation by Edmond Barbier was published in 1876.[1] DELL Studio 1535 CPU Fan

A Dutch translation by Tiberius Cornelis Winkler was published in 1860.[79] By 1864, additional translations had appeared in Italian and Russian.[74] In Darwin's lifetime, Origin was published in Swedish in 1871,[80] Danish in 1872, Polish in 1873, Hungarian in 1873–1874, Spanish in 1877 and Serbian in 1878. By 1977, it had appeared in an additional 18 languages. HP Pavilion dv6736nr CPU Fan

Page ii contains quotations by William Whewell and Francis Bacon on the theology of natural laws,[82] harmonising science and religion in accordance with Isaac Newton's belief in a rational God who established a law-abiding cosmos.[83] In the second edition, Darwin added an epigraph from Joseph Butler affirming that God could work through scientific laws as much as throughmiracles, HP Envy 15-1050ca CPU Fan

in a nod to the religious concerns of his oldest friends.[62] The Introduction establishes Darwin's credentials as a naturalist and author,[84] then refers to John Herschel's letter suggesting that the origin of species "would be found to be a natural in contradistinction to a miraculous process":HP Pavilion dv7-6100et CPU Fan

WHEN on board H.M.S. 'Beagle,' as naturalist, I was much struck with certain facts in the distribution of the inhabitants of South America, and in the geological relations of the present to the past inhabitants of that continent. These facts seemed to me to throw some light on the origin of species—that mystery of mysteries, as it has been called by one of our greatest philosophers. APPLE 661-4951 CPU Fan

Darwin refers specifically to the distribution of the species rheas, and to that of the Galápagos tortoises and mockingbirds. He mentions his years of work on his theory, and the arrival of Wallace at the same conclusion, which led him to "publish this Abstract" of his incomplete work. He outlines his ideas, and sets out the essence of his theory: IBM 42W2403 CPU Fan

As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. ACER Aspire 9304WSMi CPU Fan

From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.

Starting with the third edition, Darwin prefaced the introduction with a sketch of the historical development of evolutionary ideas.[88] 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;[89] HP 610773-001 CPU Fan

in the fourth edition he mentioned that William Charles Wells had done so as early as 1813.

Chapter I covers animal husbandry and plant breeding, going back to ancient Egypt. Darwin discusses contemporary opinions on the origins of different breeds under cultivation to argue that many have been produced from common ancestors by selective breeding.[91] IBM ThinkPad R50p 1830 CPU Fan

As an illustration of artificial selection, he describesfancy pigeon breeding,[92] noting that "[t]he diversity of the breeds is something astonishing", yet all were descended from one species of rock pigeon.[93]Darwin saw two distinct kinds of variation: (1) rare abrupt changes he called "sports" or "monstrosities" (example: ancon sheep with short legs), and (2) ubiquitous small differences (example: slightly shorter or longer bill of pigeons).[94] IBM ThinkPad T61 8898 CPU Fan

 Both types of hereditary changes can be used by breeders. However, for Darwin the small changes were most important in evolution.

In Chapter II, Darwin specifies that the distinction between species and varieties is arbitrary, with experts disagreeing and changing their decisions when new forms were found. He concludes that "a well-marked variety may be justly called an incipient species" and that "species are only strongly marked and permanent varieties".[95] IBM ThinkPad R50p 2889 CPU Fan

He argues for the ubiquity of variation in nature.[96] Historians have noted that naturalists had long been aware that the individuals of a species differed from one another, but had generally considered such variations to be limited and unimportant deviations from the archetype of each species, that archetype being a fixed ideal in the mind of God. IBM ThinkPad R50p 1830 CPU Fan

Darwin and Wallace made variation among individuals of the same species central to understanding the natural world.

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";[97] 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." IBM ThinkPad R50 1829 CPU Fan

Owing to this struggle for life, any variation, however slight and from whatever cause proceeding, if it be in any degree profitable to an individual of any species, in its infinitely complex relations to other organic beings and to external nature, will tend to the preservation of that individual, and will generally be inherited by its offspring ... I have called this principle, by which each slight variation, IBM ThinkPad R50P CPU Fan

if useful, is preserved, by the term of Natural Selection, in order to mark its relation to man's power of selection.

He notes that both A. P. de Candolle and Charles Lyell had stated that all organisms are exposed to severe competition. Darwin emphasizes that he used the phrase "struggle for existence" in "a large and metaphorical sense, including dependence of one being on another"; IBM Thinkpad W500 CPU Fan

he gives examples ranging from plants struggling against drought to plants competing for birds to eat their fruit and disseminate their seeds. He describes the struggle resulting from population growth: "It is the doctrine of Malthus applied with manifold force to the whole animal and vegetable kingdoms." He discusses checks to such increase including complex ecological interdependencies, Compaq Presario CQ41-206TU CPU Fan

and notes that competition is most severe between closely related forms "which fill nearly the same place in the economy of nature".[99]

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".[100]  SONY Vaio VPC-EB4X1E/BQ CPU Fan

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: HP G62-374CA CPU Fan

But how, it may be asked, can any analogous principle apply in nature? I believe it can and does apply most efficiently, from the simple circumstance that the more diversified the descendants from any one species become in structure, constitution, and habits, by so much will they be better enabled to seize on many and widely diversified places in the polity of nature, and so be enabled to increase in numbers. HP Pavilion dv5-1203eg CPU Fan

Historians have remarked that here Darwin anticipated the modern concept of an ecological niche.[102] He did not suggest that every favourable variation must be selected, nor that the favoured animals were better or higher, but merely more adapted to their surroundings.

Darwin proposes sexual selection, driven by competition between males for mates, HP Pavilion dv7-3131ez CPU Fan

to explain sexually dimorphic features such as lion manes, deer antlers, peacock tails, bird songs, and the bright plumage of some male birds.[103] He analysed sexual selection more fully in The Descent of Man, and Selection in Relation to Sex (1871). Natural selection was expected to work very slowly in forming new species, Dell Vostro 3450 CPU Fan

but given the effectiveness of artificial selection, he could "see no limit to the amount of change, to the beauty and infinite complexity of the coadaptations between all organic beings, one with another and with their physical conditions of life, which may be effected in the long course of time by nature's power of selection". SONY Vaio VGN-CR23/N CPU Fan

Using a tree diagram and calculations, he indicates the "divergence of character" from original species into new species and genera. He describes branches falling off as extinction occurred, while new branches formed in "the great Tree of life ... with its ever branching and beautiful ramifications".

In Darwin's time there was no agreed-upon model of heredity;[105] in Chapter I Darwin admitted, HP Pavilion dv6-3043tx CPU Fan

"The laws governing inheritance are quite unknown."[106] 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; HP Pavilion dv6-3163eo CPU Fan

and that such modifications are inherited", and that this also applied in nature.[107] 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.HP Pavilion dv7-1003eo CPU Fan

Darwin also admitted ignorance of the source of inheritable variations, but speculated they might be produced by environmental factors.[108][109] 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.[94] Dell Vostro 3450 CPU Fan

 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.  HP Pavilion dv7-3067nr CPU Fan

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.[110][111]

More detail was given in Darwin's 1868 book on The Variation of Animals and Plants under Domestication, which tried to explain heredity through his hypothesis of pangenesis. SONY Vaio VGN-CR23/N CPU Fan

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