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He saw that the autonomy of nature was a sign of God's goodness, and detected no conflict between a divinely created universe and the idea that the universe had developed over time through natural mechanisms. Aquinas rather held that: It is as if the shipbuilder were able to give to timbers that by which they would move themselves to take the form of a ship. He wrote of natural modifications occurring during reproduction and accumulating over the course of many generations, producing races and even new species, a description that anticipated in general terms the concept of natural selection.
Maupertuis' ideas were in opposition to the influence of early taxonomists like John Ray. In the late 17th century, Ray had given the first formal definition of a biological species, which he described as being characterized by essential unchanging features, and stated the seed of one species could never give rise to another. The word evolution from the Latin evolutio , meaning "to unroll like a scroll" was initially used to refer to embryological development ; its first use in relation to development of species came in , when Charles Bonnet used it for his concept of " pre-formation ," in which females carried a miniature form of all future generations.
The term gradually gained a more general meaning of growth or progressive development. Later in the 18th century, the French philosopher Georges-Louis Leclerc, Comte de Buffon , one of the leading naturalists of the time, suggested that what most people referred to as species were really just well-marked varieties, modified from an original form by environmental factors.
For example, he believed that lions, tigers, leopards and house cats might all have a common ancestor. He further speculated that the or so species of mammals then known might have descended from as few as 38 original animal forms. Buffon's evolutionary ideas were limited; he believed each of the original forms had arisen through spontaneous generation and that each was shaped by "internal moulds" that limited the amount of change.
In , Georges Cuvier published his findings on the differences between living elephants and those found in the fossil record. His analysis identified mammoths and mastodons as distinct species, different from any living animal, and effectively ended a long-running debate over whether a species could become extinct.
Independently, in , Cuvier and Alexandre Brongniart published an influential study of the geologic history of the region around Paris, based on the stratigraphic succession of rock layers. These works helped establish the antiquity of the Earth. Knowledge of the fossil record continued to advance rapidly during the first few decades of the 19th century.
By the s, the outlines of the geologic timescale were becoming clear, and in John Phillips named three major eras, based on the predominant fauna of each: This progressive picture of the history of life was accepted even by conservative English geologists like Adam Sedgwick and William Buckland ; however, like Cuvier, they attributed the progression to repeated catastrophic episodes of extinction followed by new episodes of creation. From to , geologist Charles Lyell published his multi-volume work Principles of Geology , which, building on Hutton's ideas, advocated a uniformitarian alternative to the catastrophic theory of geology.
Lyell claimed that, rather than being the products of cataclysmic and possibly supernatural events, the geologic features of the Earth are better explained as the result of the same gradual geologic forces observable in the present day—but acting over immensely long periods of time.
Although Lyell opposed evolutionary ideas even questioning the consensus that the fossil record demonstrates a true progression , his concept that the Earth was shaped by forces working gradually over an extended period, and the immense age of the Earth assumed by his theories, would strongly influence future evolutionary thinkers such as Charles Darwin. Jean-Baptiste Lamarck proposed, in his Philosophie Zoologique of , a theory of the transmutation of species transformisme.
Lamarck did not believe that all living things shared a common ancestor but rather that simple forms of life were created continuously by spontaneous generation. He also believed that an innate life force drove species to become more complex over time, advancing up a linear ladder of complexity that was related to the great chain of being. Lamarck recognized that species adapted to their environment. He explained this by saying that the same innate force driving increasing complexity caused the organs of an animal or a plant to change based on the use or disuse of those organs, just as exercise affects muscles.
He argued that these changes would be inherited by the next generation and produce slow adaptation to the environment. It was this secondary mechanism of adaptation through the inheritance of acquired characteristics that would become known as Lamarckism and would influence discussions of evolution into the 20th century. A radical British school of comparative anatomy that included the anatomist Robert Edmond Grant was closely in touch with Lamarck's French school of Transformationism.
Grant became an authority on the anatomy and reproduction of marine invertebrates. He developed Lamarck's and Erasmus Darwin's ideas of transmutation and evolutionism , and investigated homology, even proposing that plants and animals had a common evolutionary starting point. As a young student, Charles Darwin joined Grant in investigations of the life cycle of marine animals. In , an anonymous paper, probably written by Robert Jameson , praised Lamarck for explaining how higher animals had "evolved" from the simplest worms; this was the first use of the word "evolved" in a modern sense.
In , the Scottish publisher Robert Chambers anonymously published an extremely controversial but widely read book entitled Vestiges of the Natural History of Creation. This book proposed an evolutionary scenario for the origins of the Solar System and of life on Earth. It claimed that the fossil record showed a progressive ascent of animals, with current animals branching off a main line that leads progressively to humanity.
It implied that the transmutations lead to the unfolding of a preordained plan that had been woven into the laws that governed the universe. In this sense it was less completely materialistic than the ideas of radicals like Grant, but its implication that humans were only the last step in the ascent of animal life incensed many conservative thinkers. The high profile of the public debate over Vestiges , with its depiction of evolution as a progressive process , would greatly influence the perception of Darwin's theory a decade later.
Ideas about the transmutation of species were associated with the radical materialism of the Enlightenment and were attacked by more conservative thinkers. Cuvier attacked the ideas of Lamarck and Geoffroy, agreeing with Aristotle that species were immutable. Cuvier believed that the individual parts of an animal were too closely correlated with one another to allow for one part of the anatomy to change in isolation from the others, and argued that the fossil record showed patterns of catastrophic extinctions followed by repopulation, rather than gradual change over time.
He also noted that drawings of animals and animal mummies from Egypt , which were thousands of years old, showed no signs of change when compared with modern animals. The strength of Cuvier's arguments and his scientific reputation helped keep transmutational ideas out of the mainstream for decades. In Great Britain , the philosophy of natural theology remained influential. William Paley 's book Natural Theology with its famous watchmaker analogy had been written at least in part as a response to the transmutational ideas of Erasmus Darwin.
They believed that relationships between species could be discerned from developmental patterns in embryology, as well as in the fossil record, but that these relationships represented an underlying pattern of divine thought, with progressive creation leading to increasing complexity and culminating in humanity. Owen developed the idea of "archetypes" in the Divine mind that would produce a sequence of species related by anatomical homologies, such as vertebrate limbs.
Owen led a public campaign that successfully marginalized Grant in the scientific community. Darwin would make good use of the homologies analyzed by Owen in his own theory, but the harsh treatment of Grant, and the controversy surrounding Vestiges , showed him the need to ensure that his own ideas were scientifically sound. It is possible to look through the history of biology from the ancient Greeks onwards and discover anticipations of almost all of Charles Darwin's key ideas. For example, Loren Eiseley has found isolated passages written by Buffon suggesting he was almost ready to piece together a theory of natural selection, but states that such anticipations should not be taken out of the full context of the writings or of cultural values of the time which made Darwinian ideas of evolution unthinkable.
When Darwin was developing his theory, he investigated selective breeding and was impressed by Sebright 's observation that "A severe winter, or a scarcity of food, by destroying the weak and the unhealthy, has all the good effects of the most skilful selection" so that "the weak and the unhealthy do not live to propagate their infirmities.
Darwin was struck by Thomas Robert Malthus ' phrase "struggle for existence" used of warring human tribes. Several writers anticipated evolutionary aspects of Darwin's theory, and in the third edition of On the Origin of Species published in 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.
In , William Charles Wells read before the Royal Society essays assuming that there had been evolution of humans, and recognising the principle of natural selection. Darwin and Alfred Russel Wallace were unaware of this work when they jointly published the theory in , 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 , and "he distinctly recognises the principle of natural selection, and this is the first recognition which has been indicated; but he applies it only to the races of man, and to certain characters alone.
Patrick Matthew wrote in his book On Naval Timber and Arboriculture of "continual balancing of life to circumstance. 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 scattered passages in an Appendix to a work on a different subject He clearly saw, however, the full force of the principle of natural selection. 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.
But that suggestion is the central idea of the 'Origin of Species,' and contains the quintessence of Darwinism.www.cantinesanpancrazio.it/components/dyhehot/335-come-spiare-telefonate.php
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Darwin's observations led him to view transmutation as a process of divergence and branching, rather than the ladder-like progression envisioned by Jean-Baptiste Lamarck and others. In he read the new 6th edition of An Essay on the Principle of Population , written in the late 18th century by Thomas Robert 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. However, he did share them with certain other naturalists and friends, starting with Joseph Dalton Hooker , with whom he discussed his unpublished 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. In September he began full-time work on writing his book on natural selection. 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.
By , 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. In February , 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 essay along with Wallace's letter. Darwin also began work on a short abstract summarising his theory, which he would publish in as On the Origin of Species.
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By the s, whether or not species evolved was a subject of intense debate, with prominent scientists arguing both sides of the issue. He also provided the first cogent mechanism by which evolutionary change could persist: 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 Jean-Baptiste Lamarck and Vestiges of the Natural History of Creation , 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.
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By the early s in English-speaking countries, thanks partly to these efforts, evolution had become the mainstream scientific explanation for the origin of species. 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. An exception to this was Germany , where both August Weismann and Ernst Haeckel championed 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. Darwin's theory succeeded in profoundly altering scientific opinion regarding the development of life and in producing a small philosophical revolution.
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, proved to be useful for statistical models of evolution that were developed by his cousin Francis 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 in Vestiges of the Natural History of Creation that humans had arisen from animals by a process of transmutation. Therefore, he almost completely ignored the topic of human evolution in On 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. However, a series of archaeological discoveries in the s and s showed stone tools associated with the remains of extinct animals. By the early s, as summarized in Charles Lyell's book Geological 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.
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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 s were either of anatomically modern humans or of Neanderthals that were too close, especially in the critical characteristic of cranial capacity, to modern humans for them to be convincing intermediates between humans and other primates. Therefore, the debate that immediately followed the publication of On the Origin of Species centered on the similarities and differences between humans and modern apes.
Carolus Linnaeus had been criticised in the 18th century for grouping humans and apes together as primates in his ground breaking classification system. 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 gorillas lacked a structure present in human brains.
Huxley summarized his argument in his highly influential book Evidence as to Man's Place in Nature. Another viewpoint was advocated by 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. 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, 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. The four major alternatives to natural selection in the late 19th century were theistic evolution , neo-Lamarckism , orthogenesis , and saltationism. Alternatives supported by biologists at other times included structuralism , Georges Cuvier 's teleological but non-evolutionary functionalism, and vitalism.
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. 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 , theistic evolution had largely disappeared from professional scientific discussions, although it retained a strong popular following. 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. 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's recapitulation theory of evolution, which held that the embryological development of an organism repeats its evolutionary history.
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. 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. 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, Thomas Hunt Morgan.
It became the basis of the mutation theory of evolution. The rediscovery of Gregor Mendel 's laws of inheritance in 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. 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, 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.
When Thomas Hunt 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 and reconfirmed Mendelian genetics and provided solid experimental evidence linking it to chromosomal inheritance. 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.
A key step was the work of the British biologist and statistician Ronald Fisher. In a series of papers starting in and culminating in his 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. In a series of papers beginning in , another British geneticist, J.
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. 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 , Wright introduced the concept of an adaptive landscape and argued that genetic drift and inbreeding could drive a small, 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. In the first few decades of the 20th century, most field naturalists continued to believe that alternative mechanisms of evolution such as Lamarckism and orthogenesis provided the best explanation for the complexity they observed in the living world.
But as the field of genetics continued to develop, those views became less tenable. He helped to bridge the divide between the foundations of microevolution developed by the population geneticists and the patterns of macroevolution observed by field biologists, with his book Genetics and the Origin of Species. Dobzhansky examined the genetic diversity of wild populations and showed that, contrary to the assumptions of the population geneticists, these populations had large amounts of genetic diversity, with marked differences between sub-populations.
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The book also took the highly mathematical work of the population geneticists and put it into a more accessible form. Ford , the pioneer of ecological genetics , continued throughout the s and s to demonstrate the power of selection due to ecological factors including the ability to maintain genetic diversity through genetic polymorphisms such as human blood types.
Ford's work would contribute to a shift in emphasis during the course of the modern synthesis towards natural selection over genetic drift. The evolutionary biologist Ernst Mayr was influenced by the work of the German biologist Bernhard Rensch showing the influence of local environmental factors on the geographic distribution of sub-species and closely related species.
Mayr followed up on Dobzhansky's work with the book Systematics and the Origin of Species , which emphasized the importance of allopatric speciation in the formation of new species. This form of speciation occurs when the geographical isolation of a sub-population is followed by the development of mechanisms for reproductive isolation.
Mayr also formulated the biological species concept that defined a species as a group of interbreeding or potentially interbreeding populations that were reproductively isolated from all other populations. In the book Tempo and Mode in Evolution , George Gaylord Simpson showed that the fossil record was consistent with the irregular non-directional pattern predicted by the developing evolutionary synthesis, and that the linear trends that earlier paleontologists had claimed supported orthogenesis and neo-Lamarckism did not hold up to closer examination.
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