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- __NOEDITSECTION__ [[English name::| ]][[English name (linked)::| ]][[Card image::| ]] [[Card type:: Card| ]][[Card type (short)::[[ Card|]]| ]][[Attribute::| ]][[Type::| ]] [[Lore::Activate only during your opponent's turn. Destroy 1 face-up monster your opponent controls, and Special Summon 1 "Selection Token" with the same Level, Type, Attribute, ATK, and DEF as the destroyed monster. The "Selection Token" is destroyed during the End Phase.| ]] [[?ATK::| ]][[ATK string::| ]][[?DEF::| ]][[DEF string::| ]][[Property::Normal Card| ]][[Property (short)::[[Normal Card|Normal]]| ]] Main card page: "[[Main card page::|]]" [[File:|link=File:|px]]
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- Natural Selection — модификация для Half-Life.
- The story relates to Kestrel, and is an ongoing project, describing RP events as they happen, and as Kes sees them. The stories may be used IC within reason (barring the piece titled, The request). Text copyrighted to Auburn, plagiarists will be keelhauled and fed to rabid weasels.
- Natural Selection is the process by which the most favorable alleles of genes are inherited by offspring. It is one of the major driving forces of evolution and was pioneered by Charles Darwin after his voyage to the Galapagos Islands.
- Natural selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations. It is a key mechanism of evolution.
- Natural Selection is the mechanism by means of which random mutations of the DNA of individuals in a population of one species result in the non-random survival of those individuals in whom the mutation confers an advantage over those without the mutation. While it is believed that most mutations are lethal, resulting in the individual's death, some mutations are not, and can prove helpful to the individual. For example, if a mutation in a gene changed the colour of a pale coloured moth to black, the population might, over time, evolve a preponderance of black individuals if that helped them to hide more effectively from predators. This was actually observed in England where a speckled light brown species of moth became black over time during a period when the Industrial Revolution had coated many trees and buildings in black soot against which a white moth would stand out clearly to any predator. See Peppered moth evolution
- Darwin's concept of natural selection does not apply to Chuck Norris, as he is the one making the selections. Also, the theory of evolution does not exist, only species that Chuck Norris allows to live. Dinosuars died not by a meteor, but by Chuck Norris roundhouse kicking the Earth.
- Natural selection is the process by which an species of organism adapts to its environment over several generations. It is a cornerstone of Charles Darwin's theory of evolution. In the case of Norns and other Creatures, natural selection is similar to letting them breed on their own without any interaction or selective breeding. The natural selection process is based on the principle of "survival of the fittest." For example: 1.
* A population of Norns lives in a certain world. The vast majority of these Norns are from early generations with few mutations. 2.
* An infectious disease attacks the Norn population. Most of the Norns die, but a very small number of them have a gene which allows them to survive it. 3.
* The surviving Norns pass on the disease-resistance gene to their offspring. 4.
* The next generation will have a far higher percentage of Norns which are resistant to the disease, and the next time it besets the population, more Norns will survive. So, in this example, the Norns with the disease-survival gene were the "fittest", and thus survived to reproduce. Meanwhile, those who did not possess this gene perished, preventing this lack of resistance from continuing in the population. These mutations which are passed on slowly change the population over time. Generally, only mutations which are beneficial exist for any siginificant time in the population; bad mutations are eliminated by the same process outlined above. Mutations which help an organism in its environment are called "adaptations", and are developed over several generations.
- Bob finds himself remembering his "Unit Selection" test while he is trying to save the lives of his translator and himself after their heliopter crashes in a remote area of Russia.
- "Natural Selection" is the 793rd episode of Casualty and the 12th episode of the 26th series.
- Natural selection is a mechanism of evolution in which the individuals in a population possessing desirable traits survive and reproduce. The desirable traits become more prevalent in the population, and evolution occurs.
- Natural Selection is the gradual process by which heritable biological traits become either more or less common in a population as a function of the effect of inherited traits on the differential reproductive success of organisms interacting with their environment. It is a key mechanism of evolution. First compared the Replicator plan to wipe out the galaxy to natural selection. (SG1: "Unnatural Selection")
- a natural process that results in the survival and reproductive success of individuals or groups best adjusted to their environment and that leads to the perpetuation of genetic qualities best suited to that particular environmen
- Natural selection is a simple tautology that should really be obvious.
- {Other uses|Natural Selection (disambiguation)}} {{Use British English|date=January 2015}} {{Evolutionary biology}} '''Natural selection''' is the differential survival and reproduction of individuals due to differences in [[phenotype]];{{harvnb|Zimmer|Emlen|2013}} it is a key mechanism of [[evolution]]. The term "natural selection" was popularised by [[Charles Darwin]], who intended it to be compared with artificial selection, now more commonly referred to as [[selective breeding]]. [[Genetic diversity|Variation]] exists within all [[population]]s of [[organism]]s. This occurs partly because random [[mutation]]s arise in the [[genome]] of an individual organism, and these mutations can be passed to [[offspring]]. Throughout the individuals’ lives, their genomes interact with their environments to cause variations in [[Phenotypic trait|trait]]s. (The environment of a genome includes the molecular biology in the [[Cell (biology)|cell]], other cells, other individuals, populations, [[species]], as well as the abiotic environment.) Individuals with certain variants of the trait may survive and reproduce more than individuals with other, less successful, variants. Therefore, the population evolves. Factors that affect reproductive success are also important, an issue that Darwin developed in his ideas on [[sexual selection]], which was redefined as being included in natural selection in the 1930s when biologists considered it not to be very important,{{harvnb|Miller|2000|p=8}} and [[fecundity selection]], for example. Natural selection acts on the phenotype, or the observable characteristics of an organism, but the [[Genetics|genetic]] (heritable) basis of any phenotype that gives a reproductive advantage may become more common in a population (see [[allele frequency]]). Over time, this process can result in populations that specialise for particular [[ecological niche]]s ([[microevolution]]) and may eventually result in the [[speciation|emergence of new species]] ([[macroevolution]]). In other words, natural selection is an important process (though not the only process) by which evolution takes place within a population of organisms. Natural selection can be contrasted with artificial selection, in which [[human]]s intentionally choose specific traits (although they may not always get what they want). In natural selection there is no intentional choice. In other words, artificial selection is [[Teleology|teleological]] and natural selection is not teleological. Natural selection is one of the cornerstones of modern [[biology]]. The concept was published by Darwin and [[Alfred Russel Wallace]] in a [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection|joint presentation of papers in 1858]], and set out in Darwin's influential 1859 book ''[[On the Origin of Species]]'',{{harvnb|Darwin|1859}} in which natural selection was described as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favoured for reproduction. The concept of natural selection was originally developed in the absence of a valid theory of [[heredity]]; at the time of Darwin's writing, nothing was known of modern genetics. The union of traditional [[Darwinism|Darwinian evolution]] with subsequent discoveries in [[classical genetics|classical]] and [[molecular genetics]] is termed the ''[[modern evolutionary synthesis]]''. Natural selection remains the primary explanation for [[Adaptation|adaptive evolution]]. ==General principles== [[File:Lichte en zwarte versie berkenspanner.jpg|thumb|Morpha ''typica'' and morpha ''carbonaria'', [[Morph (zoology)|morphs]] of the [[peppered moth]] resting on the same tree. The light-coloured morpha ''typica'' (below the bark's scar) is hard to see on this pollution-free tree, [[camouflage|camouflaging]] it from [[predator]]s.]] [[File:Biston betularia male.jpg|thumb|right|240px|Male peppered moth]] Natural variation occurs among the individuals of any population of organisms. Many of these differences do not affect survival or reproduction, but some differences may improve the chances of survival and reproduction of a particular individual. A [[rabbit]] that runs faster than others may be more likely to escape from [[predator]]s, and [[algae]] that are more efficient at extracting energy from [[sunlight]] will grow faster. Something that increases an organism's chances of survival will often also include its reproductive rate; however, sometimes there is a trade-off between survival and current reproduction. Ultimately, what matters is total lifetime reproduction of the organism. The [[peppered moth]] exists in both light and dark colours in the [[United Kingdom]], but during the [[industrial revolution]], many of the trees on which the moths rested became blackened by [[soot]], giving the dark-coloured moths an advantage in hiding from predators. This gave dark-coloured moths a better chance of surviving to produce dark-coloured offspring, and in just fifty years from the first dark moth being caught, nearly all of the moths in industrial [[Manchester]] were dark. The balance was reversed by the effect of the [[Clean Air Act 1956]], and the dark moths became rare again, demonstrating the influence of natural selection on [[peppered moth evolution]].{{cite web |url=http://www.millerandlevine.com/km/evol/Moths/moths.html |title=The Peppered Moth - An Update |last=Miller |first=Kenneth R. |authorlink=Kenneth R. Miller |date=August 1999 |website=millerandlevine.com |publisher=Miller And Levine Biology |location=Rehoboth, MA |accessdate=2011-04-13}} If the traits that give these individuals a reproductive advantage are also heritable, that is, passed from parent to offspring, then there will be a slightly higher proportion of fast rabbits or efficient algae in the next generation. This is known as ''differential reproduction''. Even if the reproductive advantage is very slight, over many generations any heritable advantage will become dominant in the population. In this way the [[natural environment]] of an organism "selects" for traits that confer a reproductive advantage, causing gradual changes or evolution of [[life]]. This effect was first described and named by Charles Darwin. The concept of natural selection predates the understanding of genetics, the mechanism of heredity for all known life forms. In modern terms, selection acts on an organism's phenotype, or observable characteristics, but it is the organism's genetic make-up or [[genotype]] that is [[Heritability|inherited]]. The phenotype is the result of the genotype and the environment in which the organism lives (see [[Genotype-phenotype distinction]]). This is the link between natural selection and genetics, as described in the [[modern evolutionary synthesis]]. Although a complete theory of evolution also requires an account of how [[genetic variation]] arises in the first place (such as by mutation and [[sexual reproduction]]) and includes other evolutionary mechanisms (such as [[genetic drift]] and [[gene flow]]), natural selection appears to be the most important mechanism for creating complex [[adaptation]]s in nature. ===Nomenclature and usage=== The term ''natural selection'' has slightly different definitions in different contexts. It is most often defined to operate on heritable traits, because these are the traits that directly participate in evolution. However, natural selection is "blind" in the sense that changes in phenotype (physical and behavioural characteristics) can give a reproductive advantage regardless of whether or not the trait is heritable (non heritable traits can be the result of environmental factors or the life experience of the organism). Following Darwin's primary usage the term is often used to refer to both the evolutionary consequence of blind selection and to its mechanisms.{{harvnb|Fisher|1930}}Works employing or describing this usage:
* {{harvnb|Williams|1966}}
* {{harvnb|Endler|1986}} It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects; when this distinction is important, scientists define "natural selection" specifically as "those mechanisms that contribute to the selection of individuals that reproduce," without regard to whether the basis of the selection is heritable. This is sometimes referred to as "phenotypic natural selection."Works employing or describing this usage:
* {{harvnb|Haldane|1954}}
* {{cite journal |last1=Lande |first1=Russell |authorlink1=Russell Lande |last2=Arnold |first2=Stevan J. |date=November 1983 |title=The Measurement of Selection on Correlated Characters |journal=[[Evolution (journal)|Evolution]] |location=New York |publisher=[[John Wiley & Sons]] for the [[Society for the Study of Evolution]] |volume=37 |issue=6 |pages=1210–1226 |doi=10.2307/2408842 |jstor=2408842}}
* {{harvnb|Futuyma|2005}} Traits that cause greater reproductive success of an organism are said to be selected for, whereas those that reduce success are selected against. Selection for a trait may also result in the selection of other correlated traits that do not themselves directly influence reproductive advantage. This may occur as a result of [[pleiotropy]] or [[gene linkage]].{{harvnb|Sober|1993}} ===Fitness=== [[Image:Darwin's finches.jpeg|thumb|[[Charles Darwin]]'s illustrations of beak variation in the [[Darwin's finches|finches]] of the [[Galápagos Islands]], which hold 13 closely related [[species]] that differ most markedly in the shape of their beaks. The beak of each species is suited to its preferred food, suggesting that beak shapes evolved by natural selection.]] {{Main|Fitness (biology)}} The concept of fitness is central to natural selection. In broad terms, individuals that are more "fit" have better potential for survival, as in the well-known phrase "[[survival of the fittest]]." However, as with natural selection above, the precise meaning of the term is much more subtle. Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes will become more common in the adult population of the next generation. Though natural selection acts on individuals, the effects of chance mean that fitness can only really be defined "on average" for the individuals within a population. The fitness of a particular genotype corresponds to the average effect on all individuals with that genotype. Very low-fitness genotypes cause their bearers to have few or no offspring on average; examples include many human [[genetic disorder]]s like [[cystic fibrosis]]. Since fitness is an averaged quantity, it is also possible that a favourable mutation arises in an individual that does not survive to adulthood for unrelated reasons. Fitness also depends crucially upon the environment. Conditions like [[Sickle-cell disease|sickle-cell anaemia]] may have low fitness in the general human population, but because the [[sickle cell trait]] confers immunity from [[malaria]], it has high fitness value in populations that have high malaria infection rates. ===Types of selection=== Natural selection can act on any heritable [[phenotypic trait]], and selective pressure can be produced by any aspect of the environment, including sexual selection and [[Competition (biology)|competition]] with members of the same or other species. However, this does not imply that natural selection is always directional and results in adaptive evolution; natural selection often results in the maintenance of the status quo by eliminating less fit variants. [[File:Genetic Distribution.svg|thumb|These charts depict the different types of genetic selection. On each graph, the x-axis variable is the type of [[phenotypic trait]] and the y-axis variable is the amount of organisms. Group A is the original population and Group B is the population after selection. Graph 1 shows [[directional selection]], in which a single extreme [[phenotype]] is favored. Graph 2 depicts [[stabilizing selection]], where the intermediate phenotype is favored over the extreme traits. Graph 3 shows disruptive selection, in which the extreme phenotypes are favored over the intermediate.]] Selection can be classified according to its effect on a trait. [[Stabilizing selection]] acts to hold a trait at a stable optimum, and in the simplest case all deviations from this optimum are selectively disadvantageous. [[Directional selection]] acts during transition periods, when the current mode of the trait is sub-optimal, and alters the trait towards a single new optimum. [[Disruptive selection]] also acts during transition periods when the current mode is sub-optimal, but alters the trait in more than one direction. In particular, if the trait is quantitative and [[univariate]] then both higher and lower trait levels are favoured. Disruptive selection can be a precursor to [[speciation]]. Selection can also be classified according to its effect on allele frequency. [[Directional selection|Positive selection]] acts to increase the frequency of an [[allele]]. [[Negative selection (natural selection)|Negative selection]] acts to decrease the frequency of an allele. Note that for a diallelic locus, positive selection on one allele perforce implies negative selection on the other allele. Selection can also be classified according to its effect on [[genetic diversity]]. [[Negative selection (natural selection)|Purifying selection]] acts to remove genetic variation from the population (and is opposed by [[Mutation#By inheritance|''de novo'' mutation]], which introduces new variation). [[Balancing selection]] acts to maintain genetic variation in a population (even in the absence of ''de novo'' mutation). Mechanisms include negative [[frequency-dependent selection]] (of which [[heterozygote advantage]] is a special case), and spatial and/or temporal fluctuations in the strength and direction of selection. [[Image:Life cycle of a sexually reproducing organism.svg|thumb|right|The [[Biological life cycle|life cycle]] of a sexually reproducing organism. Various components of natural selection are indicated for each life stage.{{harvnb|Christiansen|1984|pp=65–79}}]] Selection can also be classified according to the stage of an organism’s [[Biological life cycle|life cycle]] at which it acts. The use of terminology differs here. Some recognise just two types of selection: [[Natural selection#Types of selection|viability selection]] (or survival selection) which acts to improve the probability of survival of the organism, and fecundity selection (or fertility selection, or reproductive selection) which acts to improve the rate of reproduction, given successful survival. Others split the life cycle into further components of selection (see figure). Thus viability and survival selection may be defined separately and respectively as acting to improve the probability of survival before and after reproductive age is reached, while fecundity selection may be split into additional sub-components including sexual selection, ''gametic selection'' (acting on [[gamete]] survival) and ''compatibility selection'' (acting on [[zygote]] formation). Selection can also be classified according to the level or [[unit of selection]]. ''Individual selection'' acts at the level of the individual, in the sense that adaptions are ‘for’ the benefit of the individual, and result from selection among individuals. [[Gene selection]] acts directly at the level of the gene. In many situations, this is simply a different way of describing individual selection. However, in some cases (e.g., [[kin selection]] and [[intragenomic conflict]]), gene-level selection provides a more apt explanation of the underlying process. [[Group selection]] acts at the level of groups of organisms. The mechanism assumes that groups replicate and mutate in an analogous way to genes and individuals. There is an ongoing debate over the degree to which group selection occurs in nature. Finally, selection can be classified according to the [[Resource (biology)|resource]] being competed for. Sexual selection results from competition for mates. Sexual selection can be ''intrasexual'', as in cases of competition among individuals of the same sex in a population, or ''intersexual'', as in cases where one sex controls reproductive access by choosing among a population of available mates. Typically, sexual selection proceeds via fecundity selection, sometimes at the expense of viability. [[Ecological selection]] is natural selection via any other means than sexual selection. Alternatively, natural selection is sometimes defined as synonymous with ecological selection, and sexual selection is then classified as a separate mechanism to natural selection. This accords with Darwin’s usage of these terms, but ignores the fact that mate competition and mate choice are natural processes.{{harvnb|Mayr|2006}} Note that types of selection often act in concert. Thus Stabilizing selection typically proceeds via negative selection on rare alleles, leading to purifying selection, while directional selection typically proceeds via positive selection on an initially rare favoured allele. Ecological selection covers any mechanism of selection as a result of the environment, including relatives (e.g., kin selection, competition, and [[Infanticide (zoology)|infanticide]]). ====Sexual selection==== [[File:Peacock Flying.jpg|thumb|300px|right|The [[Peafowl|peacock]] tail in flight, a classic example of [[sexual selection]].]] [[File:Alligator Pipefish 2.jpg|240px|right|thumb|[[Alligator Pipefish]], a syngnathid]] {{Main|Sexual selection}} Sexual selection refers specifically to competition for mates,{{harvnb|Andersson|1994}} which can be ''intrasexual'', between individuals of the same sex, that is male–male competition, or ''intersexual'', where one gender [[mate choice|choose mates]]. However, some species exhibit sex-role reversed behaviour in which it is males that are most selective in mate choice; such as in some fishes of the family [[Syngnathidae]], though likely examples have also been found in [[sexual selection in amphibians]], [[sexual selection in birds]], [[sexual selection in mammals]] (including [[sexual selection in humans]]) and [[sexual selection in scaled reptiles]].{{cite journal |last1=Eens |first1=Marcel |last2=Pinxten |first2=Rianne |date=October 5, 2000 |title=Sex-role reversal in vertebrates: behavioural and endocrinological accounts |journal=Behavioural Processes |location=Amsterdam, the Netherlands |publisher=[[Elsevier]] |volume=51 |issue=1–3 |pages=135–147 |doi=10.1016/S0376-6357(00)00124-8 |issn=0376-6357 |pmid=11074317}} Phenotypic traits can be [[signalling theory|displayed]] in one sex and desired in the other sex, causing a [[positive feedback]] loop called a [[Fisherian runaway]], for example, the extravagant plumage of some male birds. An alternate theory proposed by the same [[Ronald Fisher]] in 1930 is the [[sexy son hypothesis]], that mothers will want promiscuous sons to give them large numbers of grandchildren and so will choose promiscuous fathers for their children. Aggression between members of the same sex is sometimes associated with very distinctive features, such as the antlers of [[Deer|stag]]s, which are used in combat with other stags. More generally, intrasexual selection is often associated with [[sexual dimorphism]], including differences in body size between males and females of a species.{{cite journal |last=Barlow |first=George W. |date=March 2005 |title=How Do We Decide that a Species is Sex-Role Reversed? |journal=[[The Quarterly Review of Biology]] |location=Chicago, IL |publisher=[[University of Chicago Press]] |volume=80 |issue=1 |pages=28–35 |doi=10.1086/431022 |issn=0033-5770 |pmid=15884733}} ===Examples of natural selection=== [[Image:Antibiotic resistance.svg|thumb|upright|[[Antimicrobial resistance|Resistance to antibiotics]] is increased though the survival of individuals that are immune to the effects of the antibiotic, whose offspring then inherit the resistance, creating a new population of resistant bacteria.]] A well-known example of natural selection in action is the development of [[Antimicrobial resistance|antibiotic resistance]] in [[microorganism]]s. Since the discovery of [[penicillin]] in 1928, [[antibiotics]] have been used to fight [[bacteria]]l diseases. Natural populations of bacteria contain, among their vast numbers of individual members, considerable variation in their genetic material, primarily as the result of mutations. When exposed to antibiotics, most bacteria die quickly, but some may have mutations that make them slightly less susceptible. If the exposure to antibiotics is short, these individuals will survive the treatment. This selective elimination of maladapted individuals from a population is natural selection. These surviving bacteria will then reproduce again, producing the next generation. Due to the elimination of the maladapted individuals in the past generation, this population contains more bacteria that have some resistance against the antibiotic. At the same time, new mutations occur, contributing new genetic variation to the existing genetic variation. Spontaneous mutations are very rare, and advantageous mutations are even rarer. However, populations of bacteria are large enough that a few individuals will have beneficial mutations. If a new mutation reduces their susceptibility to an antibiotic, these individuals are more likely to survive when next confronted with that antibiotic. Given enough time and repeated exposure to the antibiotic, a population of antibiotic-resistant bacteria will emerge. This new changed population of antibiotic-resistant bacteria is optimally adapted to the context it evolved in. At the same time, it is not necessarily optimally adapted any more to the old antibiotic free environment. The end result of natural selection is two populations that are both optimally adapted to their specific environment, while both perform substandard in the other environment. The widespread use and misuse of antibiotics has resulted in increased microbial resistance to antibiotics in clinical use, to the point that the [[Methicillin-resistant Staphylococcus aureus|methicillin-resistant ''Staphylococcus aureus'']] (MRSA) has been described as a "superbug" because of the threat it poses to health and its relative invulnerability to existing drugs.{{citation needed|date=April 2015}} Response strategies typically include the use of different, stronger antibiotics; however, new [[strain (biology)|strains]] of MRSA have recently emerged that are resistant even to these drugs.{{cite journal |last=Schito |first=Gian C. |date=March 2006 |title=The importance of the development of antibiotic resistance in ''Staphylococcus aureus'' |journal=Clinical Microbiology and Infection |publisher=[[Wiley-Blackwell|Blackwell Synergy]] on behalf of the European Society of Clinical Microbiology and Infectious Diseases |volume=12 |issue=Suppl s1 |pages=3–8 |pmid=16445718 |doi=10.1111/j.1469-0691.2006.01343.x |issn=1469-0691 |ref=harv}} This is an example of what is known as an [[evolutionary arms race]], in which bacteria continue to develop strains that are less susceptible to antibiotics, while medical researchers continue to develop new antibiotics that can kill them. A similar situation occurs with [[pesticide resistance]] in plants and insects. Arms races are not necessarily induced by man; a well-documented example involves the spread of a gene in the butterfly ''[[Hypolimnas bolina]]'' suppressing male-killing activity by ''[[Wolbachia]]'' bacteria parasites on the island of [[Samoa]], where the spread of the gene is known to have occurred over a period of just five years {{cite journal |last1=Charlat |first1=Sylvain |last2=Hornett |first2=Emily A. |last3=Fullard |first3=James H. |last4=Davies |first4=Neil |last5=Roderick |first5=George K. |last6=Wedell |first6=Nina |last7=Hurst |first7=Gregory D. D. |display-authors=3 |year=July 13, 2007 |title=Extraordinary Flux in Sex Ratio |journal=[[Science (journal)|Science]] |location=Washington, D.C. |publisher=[[American Association for the Advancement of Science]] |volume=317 |issue=5835 |page=214 |doi=10.1126/science.1143369 |issn=0036-8075 |pmid=17626876}} ==Evolution by means of natural selection== {{Main|Evolution|Darwinism}} A prerequisite for natural selection to result in adaptive evolution, novel traits and speciation, is the presence of heritable genetic variation that results in fitness differences. Genetic variation is the result of mutations, [[genetic recombination]]s and alterations in the [[karyotype]] (the number, shape, size and internal arrangement of the [[chromosome]]s). Any of these changes might have an effect that is highly advantageous or highly disadvantageous, but large effects are very rare. In the past, most changes in the genetic material were considered neutral or close to neutral because they occurred in [[noncoding DNA]] or resulted in a [[synonymous substitution]]. However, recent research suggests that many mutations in non-coding DNA do have slight deleterious effects.{{cite journal |last1=Kryukov |first1=Gregory V. |last2=Schmidt |first2=Steffen |last3=Sunyaev |first3=Shamil |date=August 1, 2005 |title=Small fitness effect of mutations in highly conserved non-coding regions |journal=[[Human Molecular Genetics]] |location=Oxford |publisher=[[Oxford University Press]] |volume=14 |issue=15 |pages=2221–2229 |doi=10.1093/hmg/ddi226 |issn=0964-6906 |pmid=15994173}}{{cite journal |last1=Bejerano |first1=Gill |last2=Pheasant |first2=Michael |last3=Makunin |first3=Igor |last4=Stephen |first4=Stuart |last5=Kent |first5=W. James |last6=Mattick |first6=John S. |last7=Haussler |first7=David |display-authors=3 |date=May 28, 2004 |title=Ultraconserved Elements in the Human Genome |journal=Science |location=Washington, D.C. |publisher=American Association for the Advancement of Science |volume=304 |issue=5675 |pages=1321-1325 |doi=10.1126/science.1098119 |issn=0036-8075 |pmid=15131266}} Although both mutation rates and average fitness effects of mutations are dependent on the organism, estimates from data in humans have found that a majority of mutations are slightly deleterious.{{cite journal |last1=Eyre-Walker |first1=Adam |last2=Woolfit |first2=Megan |last3=Phelps |first3=Ted |date=June 2006 |title=The Distribution of Fitness Effects of New Deleterious Amino Acid Mutations in Humans |journal=[[Genetics (journal)|Genetics]] |location=Bethesda, MD |publisher=[[Genetics Society of America]] |volume=173 |issue=2 |pages=891–900 |doi=10.1534/genetics.106.057570 |issn=0016-6731 |pmc=1526495 |pmid=16547091}} [[Image:Pavo cristatus albino001xx.jpg|right|thumb|The exuberant tail of the peacock is thought to be the result of sexual selection by females. This peacock is [[Leucism|leucistic]]; selection against leucism and [[albinism]] in nature is intense because they are easily spotted by predators or are [[koinophilia|unsuccessful in competition for mates]].]] By the definition of fitness, individuals with greater fitness are more likely to contribute offspring to the next generation, while individuals with lesser fitness are more likely to die early or fail to reproduce. As a result, alleles that on average result in greater fitness become more abundant in the next generation, while alleles that in general reduce fitness become rarer. If the selection forces remain the same for many generations, beneficial alleles become more and more abundant, until they dominate the population, while alleles with a lesser fitness disappear. In every generation, new mutations and re-combinations arise spontaneously, producing a new spectrum of phenotypes. Therefore, each new generation will be enriched by the increasing abundance of alleles that contribute to those traits that were favoured by selection, enhancing these traits over successive generations. Some mutations occur in so-called [[regulatory sequence|regulatory genes]]. Changes in these can have large effects on the phenotype of the individual because they regulate the function of many other genes. Most, but not all, mutations in regulatory genes result in non-viable zygotes. Examples of nonlethal regulatory mutations occur in [[Homeobox#Hox genes|HOX genes]] in humans, which can result in a [[cervical rib]]{{cite journal |last=Galis |first=Frietson |date=April 1999 |title=Why do almost all mammals have seven cervical vertebrae? Developmental constraints, ''Hox'' genes, and cancer |journal=[[Journal of Experimental Zoology]] |location=Hoboken, NJ |publisher=[[Wiley-Blackwell]] |volume=285 |issue=1 |pages=19–26 |doi=10.1002/(SICI)1097-010X(19990415)285:1<19::AID-JEZ3>3.0.CO;2-Z |issn=1932-5223 |pmid=10327647}} or [[polydactyly]], an increase in the number of fingers or toes.{{cite journal |last1=Zákány |first1=József |last2=Fromental-Ramain |first2=Catherine |last3=Warot |first3=Xavier |last4=Duboule |first4=Denis |authorlink4=Denis Duboule |date=December 9, 1997 |title=Regulation of number and size of digits by posterior ''Hox'' genes: A dose-dependent mechanism with potential evolutionary implications |journal=[[Proceedings of the National Academy of Sciences of the United States of America|Proc. Natl. Acad. Sci. U.S.A.]] |location=Washington, D.C. |publisher=[[National Academy of Sciences]] |volume=94 |issue=25 |pages=13695–13700 |doi=10.1073/pnas.94.25.13695 |issn=0027-8424 |pmc=28368 |pmid=9391088}} When such mutations result in a higher fitness, natural selection will favour these phenotypes and the novel trait will spread in the population. [[Image:Polydactyly 01 Lhand AP.jpg|upright|thumb|X-ray of the left hand of a ten-year-old boy with [[polydactyly]].]] Established traits are not immutable; traits that have high fitness in one environmental context may be much less fit if environmental conditions change. In the absence of natural selection to preserve such a trait, it will become more variable and deteriorate over time, possibly resulting in a [[Vestigiality|vestigial]] manifestation of the trait, also called [[evolutionary baggage]]. In many circumstances, the apparently vestigial structure may retain a limited functionality, or may be co-opted for other advantageous traits in a phenomenon known as [[Exaptation|preadaptation]]. A famous example of a vestigial structure, the [[eye]] of the [[Spalax|blind mole-rat]], is believed to retain function in [[Photoperiodism|photoperiod]] perception.{{cite journal |last1=Sanyal |first1=Somes |last2=Jansen |first2=Harry G. |last3=de Grip |first3=Willem J. |last4=Nevo |first4=Eviatar |authorlink4=Eviatar Nevo |last5=de Jong |first5=Welfried W. |display-authors=4 |date=July 1990 |title=The Eye of the Blind Mole Rat, ''Spalax ehrenbergi''. Rudiment With Hidden Function? |url=http://iovs.arvojournals.org/article.aspx?articleid=2160417 |journal=[[Investigative Ophthalmology & Visual Science]] |publisher=Association for Research in Vision and Ophthalmology |volume=31 |issue=7 |pages=1398–1404 |issn=0146-0404 |pmid=2142147 |accessdate=2015-07-28}} ===Speciation=== {{Main|Speciation}} Speciation requires cessation of gene flow, which results from [[reproductive isolation]]. Over time, isolated subgroups might diverge radically to become different species, either because of differences in selection pressures on the different subgroups, or because different mutations arise spontaneously in the different populations, or because of genetic drift which is responsible for phenomena such as [[population bottleneck|bottleneck effect]] and [[founder effect]]. A lesser-known mechanism of speciation occurs via [[Hybrid (biology)|hybrid]]isation, well-documented in plants and occasionally observed in species-rich groups of animals such as [[cichlid]] fishes.{{cite journal |last1=Salzburger |first1=Walter |last2=Baric |first2=Sanja |last3=Sturmbauer |first3=Christian |date=March 2002 |title=Speciation via introgressive hybridisation in East African cichlids? |journal=[[Molecular Ecology]] |location=Hoboken, NJ |publisher=Wiley-Blackwell |volume=11 |issue=3 |pages=619–625 |doi=10.1046/j.0962-1083.2001.01438.x |issn=0962-1083 |pmid=11918795}} Such mechanisms of rapid speciation can reflect a mechanism of evolutionary change known as [[punctuated equilibrium]], which suggests that evolutionary change and in particular speciation typically happens quickly after interrupting long periods of stasis. Genetic changes within groups result in increasing incompatibility between the genomes of the two subgroups, thus reducing gene flow between the groups. Gene flow will effectively cease when the distinctive mutations characterising each subgroup become fixed. As few as two mutations can result in speciation: if each mutation has a neutral or positive effect on fitness when they occur separately, but a negative effect when they occur together, then fixation of these genes in the respective subgroups will lead to two reproductively isolated populations. According to the biological species concept, these will be two different species. ==Historical development== {{Main|History of evolutionary thought|Inception of Darwin's theory|Development of Darwin's theory}} [[Image:Charles Darwin aged 51.jpg|right|thumb|The modern theory of natural selection derives from the work of Charles Darwin in the nineteenth century.]] ===Pre-Darwinian theories=== Several ancient philosophers expressed the idea that nature produces a huge variety of creatures, randomly, and that only those creatures that manage to provide for themselves and reproduce successfully survive; well-known examples include [[Empedocles]]{{harvnb|Empedocles|1898|loc=[https://history.hanover.edu/texts/presoc/emp.html#book2 ''On Nature'', Book II]}} and his intellectual successor, the [[Roman Republic|Roman]] poet [[Lucretius]].{{harvnb|Lucretius|1916|loc=[http://classics.mit.edu/Carus/nature_things.5.v.html ''On the Nature of Things'', Book V]}} Empedocles' idea that organisms arose entirely by the incidental workings of causes such as heat and cold was criticised by [[Aristotle]] in Book II of ''[[Physics (Aristotle)|Physics]]''.{{harvnb|Aristotle|loc=[http://classics.mit.edu/Aristotle/physics.2.ii.html ''Physics'', Book II, Chapters 4 and 8]}} He posited natural [[teleology]] in its place. He believed that form was achieved for a purpose, citing the regularity of heredity in species as proof.{{harvnb|Lear|1988|p=[https://books.google.com.ph/books?id=hSAGlzPLq7gC&lpg=PP1&pg=PA38&hl=en#v=onepage&q&f=false 38]}}{{cite journal |last=Henry |first=Devin |date=September 2006 |title=Aristotle on the Mechanism of Inheritance |url=http://works.bepress.com/cgi/viewcontent.cgi?article=1010&context=devinhenry |format=PDF |journal=Journal of the History of Biology |location=Dordrecht, the Netherlands |publisher=[[Springer Science+Business Media]] |volume=39 |issue=3 |pages=425–455 |doi=10.1007/s10739-005-3058-y |issn=0022-5010 |accessdate=2015-07-30}} Nevertheless, he acceded that new types of animals, monstrosities (τερας), can occur in very rare instances (''[[Generation of Animals]]'', Book IV).{{harvnb|Ariew|2002}} As quoted in Darwin's ''The Origin of Species'' (1872), Aristotle considered whether different forms (e.g., of teeth) might have appeared accidentally, but only the useful forms survived: {{quote|So what hinders the different parts [of the body] from having this merely accidental relation in nature? as the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident. And in like manner as to the other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity, and whatsoever things were not thus constituted, perished, and still perish.|Aristotle|''Physics'', Book II, Chapter 8{{harvnb|Darwin|1872|p=[http://darwin-online.org.uk/content/frameset?itemID=F391&viewtype=text&pageseq=18 xiii]}}}} But he rejected this possibility in the next paragraph: {{quote|...Yet it is impossible that this should be the true view. For teeth and all other natural things either invariably or normally come about in a given way; but of not one of the results of chance or spontaneity is this true. We do not ascribe to chance or mere coincidence the frequency of rain in winter, but frequent rain in summer we do; nor heat in the dog-days, but only if we have it in winter. If then, it is agreed that things are either the result of coincidence or for an end, and these cannot be the result of coincidence or spontaneity, it follows that they must be for an end; and that such things are all due to nature even the champions of the theory which is before us would agree. Therefore action for an end is present in things which come to be and are by nature.|Aristotle|''Physics'', Book II, Chapter 8{{harvnb|Aristotle|loc=[http://classics.mit.edu/Aristotle/physics.2.ii.html ''Physics'', Book II, Chapter 8]}}}} The [[Struggle for existence#Historical development|struggle for existence]] was later described by [[Islam]]ic writer [[Al-Jahiz]] in the 9th century.{{cite journal |last=Zirkle |first=Conway |authorlink=Conway Zirkle |date=April 25, 1941 |title=Natural Selection before the 'Origin of Species' |journal=[[Proceedings of the American Philosophical Society]] |location=Philadelphia, PA |publisher=[[American Philosophical Society]] |volume=84 |issue=1 |pages=71–123 |jstor=984852 |issn=0003-049X}}{{harvnb|Agutter|Wheatley|2008|p=43}} The classical arguments were reintroduced in the 18th century by [[Pierre Louis Maupertuis]]{{cite journal |last=Maupertuis |first=Pierre Louis |authorlink=Pierre Louis Maupertuis |year=1746 |title=[[s:fr:Les Loix du mouvement et du repos déduites d’un principe metaphysique|''Les Loix du mouvement et du repos déduites d’un principe metaphysique'']] |trans-title=[[s:Translation:Derivation of the laws of motion and equilibrium from a metaphysical principle#I. Assessment of the Proofs of God.27s Existence that are Based on the Marvels of Nature|"Derivation of the laws of motion and equilibrium from a metaphysical principle"]] |language=French |journal=Histoire de l'Académie Royale des Sciences et des Belles Lettres |location=Berlin |publisher=Ambroise Haude |pages=267–294 |ref=harv}} and others, including Charles Darwin's grandfather [[Erasmus Darwin]]. While these forerunners had an influence on [[Darwinism]], they later had little influence on the trajectory of evolutionary thought after Charles Darwin. Until the early 19th century, the [[History of creationism#Renaissance to Darwin|prevailing view]] in [[Western world|Western societies]] was that differences between individuals of a species were uninteresting departures from their [[Theory of Forms|Platonic ideal]]ism (or [[wikt:typus|typus]]) of [[Baraminology|created kind]]s. However, the theory of [[uniformitarianism]] in [[geology]] promoted the idea that simple, weak forces could act continuously over long periods of time to produce radical changes in the [[Earth]]'s landscape. The success of this theory raised awareness of the vast scale of [[Geologic time scale|geological time]] and made plausible the idea that tiny, virtually imperceptible changes in successive generations could produce consequences on the scale of differences between species. Early 19th-century evolutionists such as [[Jean-Baptiste Lamarck]] suggested the [[inheritance of acquired characteristics]] as a mechanism for evolutionary change; adaptive traits acquired by an organism during its lifetime could be inherited by that organism's progeny, eventually causing [[transmutation of species]].{{harvnb|Lamarck|1809}} This theory has come to be known as [[Lamarckism]] and was an influence on the anti-genetic ideas of the [[Stalinism|Stalinist]] [[Soviet Union|Soviet]] biologist [[Trofim Lysenko]].{{cite journal |last=Joravsky |first=David |date=January 1959 |title=Soviet Marxism and Biology before Lysenko |journal=[[Journal of the History of Ideas]] |location=Philadelphia, PA |publisher=[[University of Pennsylvania Press]] |volume=20 |issue=1 |pages=85–104 |doi=10.2307/2707968 |issn=0022-5037}} Between 1835 and 1837, zoologist [[Edward Blyth]] also contributed specifically to the area of variation, artificial selection, and how a similar process occurs in nature (see [[Edward Blyth#On natural selection]]). In fact, Charles Darwin showed his high regards for Blyth's ideas in the first chapter on variation of ''On the Origin of Species'' that he wrote, "Mr. Blyth, whose opinion, from his large and varied stores of knowledge, I should value more than that of almost any one, ..."{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?pageseq=33&itemID=F373&viewtype=text 18]}} ===Darwin's theory=== In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for adaptation and speciation. He defined natural selection as the "principle by which each slight variation [of a trait], if useful, is preserved."{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=76 61]}} The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them and that variation is heritable, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are inherited, then differential reproductive success will lead to a progressive evolution of particular populations of a species, and populations that evolve to be sufficiently different eventually become different species.{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=text&pageseq=20 5]}} Darwin's ideas were inspired by the observations that he had made on the [[second voyage of HMS Beagle|second voyage of HMS ''Beagle'']] (1831–1836), and by the work of a political economist, the Reverend [[Thomas Robert Malthus]], who in ''[[An Essay on the Principle of Population]]'' (1798), noted that population (if unchecked) increases exponentially, whereas the food supply grows only [[linear function|arithmetically]]; thus, inevitable limitations of resources would have demographic implications, leading to a "struggle for existence."{{harvnb|Malthus|1798}} When Darwin read Malthus in 1838 he was already primed by his work as a [[Natural history|naturalist]] to appreciate the "struggle for existence" in nature and it struck him that as population outgrew resources, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species."{{harvnb|Darwin|1958|p=[http://darwin-online.org.uk/content/frameset?viewtype=text&itemID=F1497&pageseq=124 120]}} Here is Darwin's own summary of the idea, which can be found in the fourth chapter of ''On the Origin of Species'': If during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organisation, and I think this cannot be disputed; if there be, owing to the high geometrical powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each being's own welfare, in the same way as so many variations have occurred useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterised will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will tend to produce offspring similarly characterised. This principle of preservation, I have called, for the sake of brevity, Natural Selection.{{harvnb|Darwin|1859|pp=[http://darwin-online.org.uk/content/frameset?pageseq=144&itemID=F373&viewtype=side 126–127]}} Once he had his theory "by which to work," Darwin was meticulous about gathering and refining evidence as his "prime hobby" before making his idea public. He was in the process of writing his "big book" to present his researches when the naturalist Alfred Russel Wallace independently conceived of the principle and described it in an essay he sent to Darwin to forward to [[Charles Lyell]]. Lyell and [[Joseph Dalton Hooker]] decided (without Wallace's knowledge) to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and ''[[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection]]'' was read to the [[Linnean Society of London]] announcing co-discovery of the principle in July 1858.{{harvnb|Wallace|1871}} Darwin published a detailed account of his evidence and conclusions in ''On the Origin of Species'' in 1859. In the 3rd edition of 1861 Darwin acknowledged that others—a notable one being [[William Charles Wells]] in 1813, and [[Patrick Matthew]] in 1831—had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications.{{harvnb|Darwin|1861|p=[http://darwin-online.org.uk/content/frameset?itemID=F381&viewtype=text&pageseq=20 xiii]}} Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called "artificial selection"; in his early manuscripts he referred to a ''Nature'', which would do the selection. At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: "I am convinced that Natural Selection has been the main but not exclusive means of modification."{{harvnb|Darwin|1859|p=[http://darwin-online.org.uk/content/frameset?itemID=F373&viewtype=side&pageseq=21 6]}} In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term "Natural Selection," preferring the term "Natural Preservation."{{cite web |url=http://www.darwinproject.ac.uk/entry-2931 |title=Darwin, C. R. to Lyell, Charles |last=Darwin |first=Charles |authorlink=Charles Darwin |date=September 28, 1860 |website=[[Correspondence of Charles Darwin#Darwin Correspondence Project website|Darwin Correspondence Project]] |publisher=[[Cambridge University Library]] |location=Cambridge, UK |id=Letter 2931 |accessdate=2015-08-01}} For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection. After the publication of ''On the Origin of Species'', educated people generally accepted that evolution had occurred in some form. However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its "unguided" and non-progressive nature,{{harvnb|Eisley|1958}} a response that has been characterised as the single most significant impediment to the idea's acceptance.{{harvnb|Kuhn|1996}} However, some thinkers enthusiastically embraced natural selection; after reading Darwin, [[Herbert Spencer]] introduced the term ''survival of the fittest'', which became a popular summary of the theory.{{cite web |url=http://www.darwinproject.ac.uk/entry-5145#mark-5145.f3 |title=Darwin, C. R. to Wallace, A. R. |last=Darwin |first=Charles |date=July 5, 1866 |website=Darwin Correspondence Project |publisher=Cambridge University Library |location=Cambridge, UK |id=Letter 5145 |accessdate=2010-01-12}} *{{cite journal |last=Stucke |first=Maurice E. |date=Summer 2008 |title=Better Competition Advocacy |url=http://works.bepress.com/cgi/viewcontent.cgi?article=1000&context=maurice_stucke |format=PDF |journal=St. John's Law Review |location=Jamaica, NY |publisher=[[St. John's University School of Law]] |volume=82 |number=3 |pages=951–1036 |issn=2168-8796 |accessdate=2007-08-29 |quote=This survival of the fittest, which I have here sought to express in mechanical terms, is that which Mr. Darwin has called 'natural selection, or the preservation of favoured races in the struggle for life.'}} — [[Herbert Spencer]], ''[https://archive.org/details/principlesbiolo05spengoog Principles of Biology]'' (1864), vol. 1, pp. 444–445 The fifth edition of ''On the Origin of Species'' published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: "But the expression often used by Mr. Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient."{{harvnb|Darwin|1872|p=[http://darwin-online.org.uk/content/frameset?itemID=F391&viewtype=text&pageseq=76 49].}} Although the phrase is still often used by non-biologists, modern biologists avoid it because it is [[Tautology (rhetoric)|tautological]] if "fittest" is read to mean "functionally superior" and is applied to individuals rather than considered as an averaged quantity over populations.{{cite journal |last1=Mills |first1=Susan K. |last2=Beatty |first2=John H. |year=1979 |title=The Propensity Interpretation of Fitness |url=https://mitpress.mit.edu/sites/default/files/titles/content/9780262195492_sch_0001.pdf |format=PDF |journal=[[Philosophy of Science (journal)|Philosophy of Science]] |location=Chicago, IL |publisher=University of Chicago Press on behalf of the [[Philosophy of Science Association]] |volume=46 |pages=263–286 |issn=0031-8248}} ===Modern evolutionary synthesis=== {{Main|Modern evolutionary synthesis}} Natural selection relies crucially on the idea of heredity, but developed before the basic concepts of genetics. Although the [[Moravia]]n monk [[Gregor Mendel]], the father of modern genetics, was a contemporary of Darwin's, his work would lie in obscurity until the early 20th century. Only after the 20th-century integration of Darwin's theory of evolution with a complex statistical appreciation of Gregor Mendel's "re-discovered" laws of inheritance did scientists generally come to accept natural selection. The work of Ronald Fisher (who developed the required mathematical language and wrote ''[[The Genetical Theory of Natural Selection]]'' (1930)), [[J. B. S. Haldane]] (who introduced the concept of the "cost" of natural selection),{{harvnb|Haldane|1932}} *{{cite journal |last=Haldane |first=J. B. S. |authorlink=J. B. S. Haldane |date=December 1957 |title=The Cost of Natural Selection |url=http://www.blackwellpublishing.com/ridley/classictexts/haldane2.pdf |format=PDF |journal=[[Journal of Genetics]] |volume=55 |issue=3 |pages=511–524 |doi=10.1007/BF02984069 |issn=0022-1333 |accessdate=2015-08-02}} [[Sewall Wright]] (who elucidated the nature of selection and adaptation),{{cite journal |last=Wright |first=Sewall |authorlink=Sewall Wright |year=1932 |title=The roles of mutation, inbreeding, crossbreeding and selection in evolution |url=http://www.blackwellpublishing.com/ridley/classictexts/wright.asp |journal=Proceedings of the VI International Congress of Genetrics |volume=1 |pages=356–366 |accessdate=2015-08-02}} [[Theodosius Dobzhansky]] (who established the idea that mutation, by creating genetic diversity, supplied the raw material for natural selection: see ''[[Genetics and the Origin of Species]]'' (1937)),{{harvnb|Dobzhansky|1937}} *{{harvnb|Dobzhansky|1951}} [[W. D. Hamilton|William D. Hamilton]] (who conceived of kin selection), [[Ernst Mayr]] (who recognised the key importance of reproductive isolation for speciation: see ''[[Systematics and the Origin of Species]]'' (1942)){{harvnb|Mayr|1942}} and many others together formed the modern evolutionary synthesis. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today. ==Genetic basis of natural selection== The idea of natural selection predates the understanding of genetics. We now have a much better idea of the biology underlying [[heritability]], which is the basis of natural selection. ===Genotype and phenotype=== {{See also|Genotype-phenotype distinction}} Natural selection acts on an organism's phenotype, or physical characteristics. Phenotype is determined by an organism's genetic make-up (genotype) and the environment in which the organism lives. Often, natural selection acts on specific traits of an individual, and the terms phenotype and genotype are used narrowly to indicate these specific traits. When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an allele. It is this genetic variation that underlies phenotypic traits. A typical example is that certain combinations of genes for [[eye colour]] in humans that, for instance, give rise to the phenotype of blue eyes. (On the other hand, when all the organisms in a population share the same allele for a particular trait, and this state is stable over time, the allele is said to be ''[[fixation (population genetics)|fixed]]'' in that population.) Some traits are governed by only a single gene, but most traits are influenced by the interactions of many genes. A variation in one of the many genes that contributes to a trait may have only a small effect on the phenotype; together, these genes can produce a continuum of possible phenotypic values.{{harvnb|Falconer|Mackay|1996}}
- Upon Heller's arrival at Koenig's base, the Doctor continues to claim innocence, until a pair of helicopters ambush Heller. Destroying them, Heller attacks, and consumes, a commander, revealing Koenig's location. Upon arrival at the base, Heller proceeds to force it out of lockdown. He successfully breaks it, and Koenig makes his escape to a gunship, which he commissions to attack Heller. Heller easily knocks it out of the sky.
- "Natural Selection" is the third episode of the first season of the animated television series, The Spectacular Spider-Man., and marks the first appearance of "The Lizard".
- Natural selection states simply that the frequency of inherited traits that help an organism to survive tend to increase over the generations in a population. Similarly the frequencies of inherited traits that reduce the probability of an organism surviving tend to reduce over the generations. This is a tautology and inevitably true. Natural selection can happen in any situation where something reproduces and passes on its traits. Charles Darwin and Alfred Russell Wallace developed this idea independently. Natural selection affects the genes of living organisms. Over time natural selection causes populations to differentiate as they adapt to new environments. Gradually new subspecies and new species are formed. This is known as the Theory of Evolution by natural selection. In a slightly different way natural selection also affects Memes, which are ideas that people copy and pass on to other people - or more correctly ideas which cause people to copy them and pass on.
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