590 bowler, peter. 249 romero diaz, aldemaro. The biology of hypogean fishes, 2001,. 57 lustig, Abigail; Richards, robert John; Ruse, michael. Darwinian heresies, 2004,.11 bowler, peter. 432 vonnegut, kurt (1999).
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Late victorian Gothic tales, 2005,. 20 marketing Link moore, gregory; nietzsche, friedrich Wilhelm. Darwin's Screens: evolutionary aesthetics, time and Sexual Display in the cinema by barbara Creed, 2009,. 8 nietzsche, biology, and metaphor, 2002,. 117 bowler, peter. Life's splendid drama: evolutionary biology and the reconstruction of life's ancestry, 1996,. 164 bowler, peter. The eclipse of Darwinism: anti-darwinian evolution theories in the decades around 1900, 1992,. 161 bowler, peter. Evolution: the history of an idea, 1989,. 263 merits The Encyclopædia britannica: a dictionary of arts, sciences, literature and general information, volume 20, hugh Chisholm, The Encyclopædia britannica company, 1911,.
The logic of Chance: The nature and Origin of biological evolution. (2001) The principle of counter-directional morphological evolution and its mother significance for constructing the megasystem of protists and other eukaryotes. Protistology 2: 6-14,. S.; Aristotle to zoos: a philosophical Dictionary of biology; Harvard University Press 1985, isbn majerus, michael. (ed:Fellowes, m,. The peppered Moth: Decline of a darwinian Disciple; Insect evolutionary Ecology (royal Entomological Society) cabi 2005 isbn moore, james Richard. History, humanity and evolution: Essays for John. Renovating Russia: the human sciences and the fate of liberal modernity, 2008,.
In literature edit kurt Vonnegut 's 1999 novel Galápagos 23 is set offer a million years in a future where humans have "devolved" to have much smaller brains. 24 see also edit references edit mcShea d (1991). "Complexity and evolution: What everybody knows". a b c d dougherty, michael. Is the human race evolving or devolving? Scientific American July 20, 1998. "Darwin's precursors and influences: Glossary". Evolution: the modern synthesis.
Eigenmann an ichthyologist wrote cave vertebrates of America: a study in degenerative evolution (1909) in which he concluded that cave evolution was essentially degenerative. 20 The entomologist William Morton Wheeler 21 and the lamarckian Ernest MacBride (18661940) also advocated degenerative evolution. According to macbride invertebrates were actually degenerate vertebrates, his argument was based on the idea that "crawling on the seabed was inherently less stimulating than swimming in open waters." 22 Dollo's law edit main article: Dollo's law Complex organs evolve in a lineage over many. This observation is sometimes generalized to a hypothesis known as Dollo's law, which states that evolution is not reversible. This does not mean that similar engineering solutions cannot be found by natural selection. For instance the tail of the cetacea —whales, dolphins and porpoises which are evolved from formerly land-dwelling mammals—is an adaptation of the spinal column for propulsion in water. Unlike the tail of the mammal's marine ancestor, the sarcopterygii, and the other teleosts, which move from side to side, the cetacean's tail moves up and down as it flexes its mammalian spine, but the function of the tail in providing propulsion is remarkably similar.
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13 14 Anton Dohrn also developed a theory of degenerative evolution based on his studies of vertebrates. According to dohrn many chordates are degenerated because of their environmental conditions. Dohrn claimed cyclostomes such as lampreys are degenerate fish as there is no evidence their jawless state is an ancestral feature but is the product of environmental adaptation due to parasitism. According to dohrn if cyclotomes would devolve further then they would resemble something like an Amphioxus. 15 The historian of biology peter. Bowler has written that devolution was taken seriously by proponents of orthogenesis and others in the late 19th century who at this period of time firmly believed that there was a direction in evolution. Orthogenesis was the belief that evolution travels in internally directed trends and levels.
The paleontologist Alpheus hyatt discussed devolution in his work, using the concept of racial senility as the mechanism of devolution. Bowler defines racial senility as "an evolutionary money retreat back to a state resembling that from which it began." 16 hyatt who studied the fossils of invertebrates believed that up to a point ammonoids developed by regular stages up until a specific level but would later. To hyatt after the level of degeneration the species would then become extinct, according to hyatt there was a "phase of youth, a phase of maturity, a phase of senility or degeneration foreshadowing the extinction of a type". 17 18 to hyatt the devolution was predetermined by internal factors which organisms can neither control or reverse. This idea of all evolutionary branches eventually running out of energy and degenerating into extinction was a pessimistic view of evolution and was unpopular amongst many scientists of the time.
That could be seen as reversed evolution, though the concept is not of much interest because it does not differ in any functional or effective way from any other adaptation to selection pressures. 9 As the number of genetic changes rises however, one combinatorial effect is that it becomes vanishingly unlikely that the full course of adaptation can be reversed precisely. Also, if one of the original adaptations involved complete loss of a gene, one can neglect any probability of reversal. Accordingly, one might well expect reversal of peppered moth colour changes, but not reversal of the loss of limbs in snakes. History edit further information: Degeneration theory The concept of degenerative evolution was used by scientists in the 19th century, at this time it was believed by most biologists that evolution had some kind of direction. In 1857 the physician Bénédict Morel influenced by lamarckism claimed that environmental factors such as taking drugs or alcohol would produce social degeneration in the offspring of those individuals, and would revert those offspring to a primitive state.
10 Morel, a devout Catholic, had believed that mankind had started in perfection, contrasting modern humanity to the past, morel claimed there had been "Morbid deviation from an original type". 11 His theory of devolution was later advocated by some biologists. According to roger Luckhurst: Darwin soothed readers that evolution was progressive, and directed towards human perfectibility. The next generation of biologists were less confident or consoling. Using Darwin's theory, and many rival biological accounts of development then in circulation, scientists suspected that it was just as possible to devolve, to slip back down the evolutionary scale to prior states of development. 12 One of the first biologists to suggest devolution was ray lankester, he explored the possibility that evolution by natural selection may in some cases lead to devolution, an example he studied was the regressions in the life cycle of sea squirts. Lankester discussed the idea of devolution in his book degeneration: a chapter in Darwinism (1880). He was a critic of progressive evolution, pointing out that higher forms existed in the past which have since degenerated into simpler forms. Lankester argued that "if it was possible to evolve, it was also possible to devolve, and that complex organisms could devolve into simpler forms or animals".
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This report view is supported by the fossil record which demonstrates that roughly ninety-nine percent of all species that ever lived are now extinct. 2 people thinking in terms of devolution commonly assume that progress is shown by increasing complexity, but biologists studying the evolution of complexity find evidence of many examples of decreasing complexity in the record of evolution. The lower jaw in fish, reptiles and mammals has seen a decrease in complexity, if measured by the number of bones. Ancestors of modern horses had several toes on each foot; modern horses have a single hooved toe. Modern humans may be evolving towards never having wisdom teeth, and already have lost most of the tail found in many other mammals - not to mention other vestigial structures, such as the vermiform appendix or the nictitating membrane. 2 In some cases, the level of organization of living creatures can also shift downwards (e.g., the loss of multicellularity in some groups of protists and fungi). 7 A more rational version of the concept of devolution, a version that does not involve concepts of "primitive" or "advanced" organisms, is based on the observation that if certain genetic changes in a particular combination (sometimes in a particular sequence as well) are precisely. 8 At a trivial review level, where just one or a few mutations are involved, selection pressure in one direction can have one effect, which can be reversed by new patterns of selection when conditions change.
For example, it could be said that "feet are better than hooves " or " lungs are better than gills so their development is "evolutionary" whereas change to an inferior or "less advanced" structure would essay be called "devolution". In reality an evolutionary biologist defines all heritable changes to relative frequencies of the genes or indeed to epigenetic states in the gene pool as evolution. 6 All gene pool changes that lead to increased fitness in terms of appropriate aspects of reproduction are seen as (neo-)Darwinian adaptation because, for the organisms possessing the changed structures, each is a useful adaptation to their circumstances. For example, hooves have advantages for running quickly on plains, which benefits horses, and feet offer advantages in climbing trees, which some ancestors of humans did. 2 The concept of devolution as regress from progress relates to the ancient ideas that either life came into being through special creation or that humans are the ultimate product or goal of evolution. The latter belief is related to anthropocentrism, the idea that human existence is the point of all universal existence. Such thinking can lead on to the idea that species evolve because they "need to" in order to adapt to environmental changes. Biologists refer to this misconception as teleology, the idea of intrinsic finality that things are "supposed" to be and behave a certain way, and naturally tend to act that way to pursue their own good. From a biological viewpoint, in contrast, if species evolve it is not a reaction to necessity, but rather that the population contains variations with traits that favour their natural selection.
as a result of a purposeful internal drive or tendency to form improved adaptations to the environment. In contrast, darwinian evolution and its elaboration in the light of subsequent advances in biological research, have shown that adaptation through natural selection comes about when particular heritable attributes in a population happen to give a better chance of successful reproduction in the reigning environment. By the same process less advantageous attributes are less "successful they decrease in frequency or are lost completely. Since darwin's time it has been shown how these changes in the frequencies of attributes occur according to the mechanisms of genetics and the laws of inheritance originally investigated by Gregor Mendel. Combined with Darwin's original insights, genetic advances led to what has variously been called the modern evolutionary synthesis 4 or the neo-darwinism of the 20th century. In these terms evolutionary adaptation may occur most obviously through the natural selection of particular alleles. Such alleles may be long established, or they may be new mutations. Selection also might arise from more complex epigenetic or other chromosomal changes, but the fundamental requirement is that any adaptive effect must be heritable. 5 The concept of devolution on the other hand, requires that there be a preferred hierarchy of structure and function, and that evolution must mean "progress" to "more advanced" organisms.
Louis Dollo, denies the report possibility of devolution. Richard Dawkins explains Dollo's law as being simply a statement about the improbability of evolution's following precisely the same path twice. Contents, context edit lamarck's theory of evolution involved a complexifying force that progressively drives animal body plans towards higher levels, creating a ladder of phyla, as well as an adaptive force that causes animals with a given body plan to adapt to circumstances. The idea of progress in such theories permits the opposite idea of decay, seen in devolution. The idea of devolution is based at least partly on the presumption that evolution requires some sort of purposeful direction towards " increasing complexity ". Modern evolutionary theory, beginning with Darwin at least, poses no such presumption. 1 and the concept of evolutionary change is independent of either any increase in complexity of organisms sharing a gene pool, or any decrease, such as in vestigiality or in loss of genes.
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Devolution, de-evolution, or backward evolution is the notion that species can revert to supposedly more primitive forms over time. The concept is related to the idea that evolution has a purpose (teleology) and is progressive (orthogenesis), for example that feet might be better than essay hooves or lungs than gills. However, evolutionary biology makes no such assumptions, and natural selection shapes adaptations with no foreknowledge of any kind. It is possible for small changes such as in the frequency of a single gene to be reversed by chance or selection, but this is no different from the normal course of evolution. In the 19th century, when belief in orthogenesis was widespread, the idea of devolution was advocated by zoologists such. Ray lankester and, anton Dohrn, and the palaeontologists, alpheus hyatt and, carl. The idea was used. Kurt Vonnegut 's 1985 novel, galápagos, where he portrays a society that has evolved backwards to have small brains. Dollo's law of irreversibility, first stated in 1893 by the palaeontologist.