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Evolution (view source)

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[[Image:Darwin_tree_4.jpg|left|"Darwin's Tree of Life"]]
 
[[Image:Darwin_tree_4.jpg|left|"Darwin's Tree of Life"]]
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==Introduction==
    
In [[biology]], '''evolution''' is the change in the [[heritability|inherited]] [[trait (biology)|traits]] of a [[population]] from generation to generation. These traits are the [[gene expression|expression]] of [[gene]]s that are copied and passed on to offspring during [[biological reproduction|reproduction]]. [[Mutation]]s in these genes can produce new or altered traits, resulting in heritable differences ([[genetic variation]]) between organisms. New traits can also come from transfer of genes between populations, as in [[migration]], or between species, in [[horizontal gene transfer]]. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through [[natural selection]] or randomly through [[genetic drift]].
 
In [[biology]], '''evolution''' is the change in the [[heritability|inherited]] [[trait (biology)|traits]] of a [[population]] from generation to generation. These traits are the [[gene expression|expression]] of [[gene]]s that are copied and passed on to offspring during [[biological reproduction|reproduction]]. [[Mutation]]s in these genes can produce new or altered traits, resulting in heritable differences ([[genetic variation]]) between organisms. New traits can also come from transfer of genes between populations, as in [[migration]], or between species, in [[horizontal gene transfer]]. Evolution occurs when these heritable differences become more common or rare in a population, either non-randomly through [[natural selection]] or randomly through [[genetic drift]].
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Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits to become rarer. This occurs because organisms with advantageous traits pass on more copies of these traits to the next generation. The measurement of selection on correlated characters (Evolution, volume 37  Over many generations, [[adaptation]]s occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.) [http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_14] , Mechanisms: the processes of evolution
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Natural selection is a process that causes heritable traits that are helpful for survival and reproduction to become more common, and harmful traits to become rarer. This occurs because organisms with advantageous traits pass on more copies of these traits to the next generation. The measurement of selection on correlated characters (Evolution, volume 37  Over many generations, [[adaptation]]s occur through a combination of successive, small, random changes in traits, and natural selection of those variants best-suited for their environment.) [http://evolution.berkeley.edu/evolibrary/article/0_0_0/evo_14] In contrast, [[genetic drift]] produces random changes in the frequency of traits in a population. Genetic drift arises from the element of chance involved in which individuals survive and reproduce.
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Understanding Evolution,  In contrast, [[genetic drift]] produces random changes in the frequency of traits in a population. Genetic drift arises from the element of chance involved in which individuals survive and reproduce.
      
One definition of a [[species]] is a group of organisms that can reproduce with one another and produce fertile offspring. However, when a species is separated into populations that are [[reproductive isolation|prevented from interbreeding]], mutations, genetic drift, and the selection of novel traits cause the accumulation of differences over generations and the emergence of [[speciation|new species]]. Stephen Gould, The Structure of Evolutionary Theory, Belknap Press, ISBN 0-674-00613-5 . The similarities between organisms suggest that all known species are [[common descent|descended from a common ancestor]] (or ancestral gene pool) through this process of gradual divergence. {Douglas J. Futuyma, Evolution, Sinauer Associates, Sunderland, Massachusetts,  ISBN 0-87893-187-2 )
 
One definition of a [[species]] is a group of organisms that can reproduce with one another and produce fertile offspring. However, when a species is separated into populations that are [[reproductive isolation|prevented from interbreeding]], mutations, genetic drift, and the selection of novel traits cause the accumulation of differences over generations and the emergence of [[speciation|new species]]. Stephen Gould, The Structure of Evolutionary Theory, Belknap Press, ISBN 0-674-00613-5 . The similarities between organisms suggest that all known species are [[common descent|descended from a common ancestor]] (or ancestral gene pool) through this process of gradual divergence. {Douglas J. Futuyma, Evolution, Sinauer Associates, Sunderland, Massachusetts,  ISBN 0-87893-187-2 )
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There are three basic mechanisms of evolutionary change: [[natural selection]], [[genetic drift]], and [[gene flow]]. Natural selection favors genes that improve capacity for survival and reproduction. Genetic drift is the random sampling of a generation's genes during reproduction, causing random changes in the frequency of alleles, and gene flow is the transfer of genes within and between populations. The relative importance of natural selection and genetic drift in a population varies depending on the strength of the selection and the [[effective population size]], which is the number of individuals capable of breeding.[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12807795]  Natural selection usually predominates in large populations, while genetic drift dominates in small populations. The dominance of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations.[http://www.pnas.org/cgi/content/abstract/252626899v1]  As a result, changing population size can dramatically influence the course of evolution. [[Population bottleneck]]s, where the population shrinks temporarily and therefore loses genetic variation, result in a more uniform population. Bottlenecks also result from alterations in gene flow such as decreased migration, [[founder effect|expansions into new habitats]], or population subdivision.
 
There are three basic mechanisms of evolutionary change: [[natural selection]], [[genetic drift]], and [[gene flow]]. Natural selection favors genes that improve capacity for survival and reproduction. Genetic drift is the random sampling of a generation's genes during reproduction, causing random changes in the frequency of alleles, and gene flow is the transfer of genes within and between populations. The relative importance of natural selection and genetic drift in a population varies depending on the strength of the selection and the [[effective population size]], which is the number of individuals capable of breeding.[http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=12807795]  Natural selection usually predominates in large populations, while genetic drift dominates in small populations. The dominance of genetic drift in small populations can even lead to the fixation of slightly deleterious mutations.[http://www.pnas.org/cgi/content/abstract/252626899v1]  As a result, changing population size can dramatically influence the course of evolution. [[Population bottleneck]]s, where the population shrinks temporarily and therefore loses genetic variation, result in a more uniform population. Bottlenecks also result from alterations in gene flow such as decreased migration, [[founder effect|expansions into new habitats]], or population subdivision.
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==Natural selection==
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===Natural selection===
    
[[Natural selection]] is the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts:
 
[[Natural selection]] is the process by which genetic mutations that enhance reproduction become, and remain, more common in successive generations of a population. It has often been called a "self-evident" mechanism because it necessarily follows from three simple facts:
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===Adaptation===
 
===Adaptation===
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{{details|Adaptation}}
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Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing.<ref name=Darwin/> They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment.<ref>{{cite journal |author=Orr H |title=The genetic theory of adaptation: a brief history |journal=Nat. Rev. Genet. |volume=6 |issue=2 |pages=119–27 |year=2005 |pmid=15716908}}</ref> This process can cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to [[antibiotic]] selection, with mutations causing [[antibiotic resistance]] by either modifying the target of the drug, or removing the transporters that allow the drug into the cell.<ref>{{cite journal |author=Nakajima A, Sugimoto Y, Yoneyama H, Nakae T |title=High-level fluoroquinolone resistance in Pseudomonas aeruginosa due to interplay of the MexAB-OprM efflux pump and the DNA gyrase mutation |url=http://www.jstage.jst.go.jp/article/mandi/46/6/46_391/_article/-char/en |journal=Microbiol. Immunol. |volume=46 |issue=6 |pages=391–95 |year=2002 |pmid=12153116}}</ref> However, many traits that appear to be simple adaptations are in fact [[exaptation]]s: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process.<ref name=GouldStructP1235>{{wikiref |id=Gould-2002 |text=Gould 2002, pp. 1235–1236}} </ref> One example is the African lizard ''Holapsis guentheri'', which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree - an exaptation.<ref name=GouldStructP1235/>
 
Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing.<ref name=Darwin/> They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment.<ref>{{cite journal |author=Orr H |title=The genetic theory of adaptation: a brief history |journal=Nat. Rev. Genet. |volume=6 |issue=2 |pages=119–27 |year=2005 |pmid=15716908}}</ref> This process can cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to [[antibiotic]] selection, with mutations causing [[antibiotic resistance]] by either modifying the target of the drug, or removing the transporters that allow the drug into the cell.<ref>{{cite journal |author=Nakajima A, Sugimoto Y, Yoneyama H, Nakae T |title=High-level fluoroquinolone resistance in Pseudomonas aeruginosa due to interplay of the MexAB-OprM efflux pump and the DNA gyrase mutation |url=http://www.jstage.jst.go.jp/article/mandi/46/6/46_391/_article/-char/en |journal=Microbiol. Immunol. |volume=46 |issue=6 |pages=391–95 |year=2002 |pmid=12153116}}</ref> However, many traits that appear to be simple adaptations are in fact [[exaptation]]s: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process.<ref name=GouldStructP1235>{{wikiref |id=Gould-2002 |text=Gould 2002, pp. 1235–1236}} </ref> One example is the African lizard ''Holapsis guentheri'', which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree - an exaptation.<ref name=GouldStructP1235/>
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===Co-evolution===
 
===Co-evolution===
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{{details more|Co-evolution}}
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Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a [[pathogen]] and a [[host (biology)|host]], or a [[predator]] and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called [[co-evolution]].<ref>{{cite journal |author=Wade MJ |title=The co-evolutionary genetics of ecological communities |journal=Nat. Rev. Genet. |volume=8 |issue=3 |pages=185–95 |year=2007 |pmid=17279094}}</ref> An example is the production of [[tetrodotoxin]] in the [[rough-skinned newt]] and the evolution of tetrodotoxin resistance in its predator, the [[Common Garter Snake|common garter snake]]. In this predator-prey pair, an [[evolutionary arms race]] has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake.<ref>{{cite journal |author=Geffeney S, Brodie ED, Ruben PC, Brodie ED |title=Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels |journal=Science |volume=297 |issue=5585 |pages=1336–9 |year=2002 |pmid=12193784}}<br />*{{cite journal |author=Brodie ED, Ridenhour BJ, Brodie ED |title=The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts |journal=Evolution |volume=56 |issue=10 |pages=2067–82 |year=2002 |pmid=12449493}}</ref>
 
Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a [[pathogen]] and a [[host (biology)|host]], or a [[predator]] and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called [[co-evolution]].<ref>{{cite journal |author=Wade MJ |title=The co-evolutionary genetics of ecological communities |journal=Nat. Rev. Genet. |volume=8 |issue=3 |pages=185–95 |year=2007 |pmid=17279094}}</ref> An example is the production of [[tetrodotoxin]] in the [[rough-skinned newt]] and the evolution of tetrodotoxin resistance in its predator, the [[Common Garter Snake|common garter snake]]. In this predator-prey pair, an [[evolutionary arms race]] has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake.<ref>{{cite journal |author=Geffeney S, Brodie ED, Ruben PC, Brodie ED |title=Mechanisms of adaptation in a predator-prey arms race: TTX-resistant sodium channels |journal=Science |volume=297 |issue=5585 |pages=1336–9 |year=2002 |pmid=12193784}}<br />*{{cite journal |author=Brodie ED, Ridenhour BJ, Brodie ED |title=The evolutionary response of predators to dangerous prey: hotspots and coldspots in the geographic mosaic of coevolution between garter snakes and newts |journal=Evolution |volume=56 |issue=10 |pages=2067–82 |year=2002 |pmid=12449493}}</ref>
    
===Co-operation===
 
===Co-operation===
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{{details more|Co-operation (evolution)}}
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However, not all interactions between species involve conflict.<ref>{{cite journal |author=Sachs J |title=Cooperation within and among species |journal=J. Evol. Biol. |volume=19 |issue=5 |pages=1415–8; discussion 1426–36 |year=2006 |pmid=16910971}}<br />*{{cite journal |author=Nowak M |title=Five rules for the evolution of cooperation |journal=Science |volume=314 |issue=5805 |pages=1560–63 |year=2006 |pmid=17158317}}</ref> Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the [[Mycorrhiza|mycorrhizal fungi]] that grow on their roots and aid the plant in absorbing nutrients from the soil.<ref>{{cite journal |author=Paszkowski U |title=Mutualism and parasitism: the yin and yang of plant symbioses |journal=Curr. Opin. Plant Biol. |volume=9 |issue=4 |pages=364–70 |year=2006 |pmid=16713732}}</ref> This is a [[Reciprocity (evolution)|reciprocal]] relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending [[signal transduction|signals]] that suppress the plant [[immune system]].<ref>{{cite journal |author=Hause B, Fester T |title=Molecular and cell biology of arbuscular mycorrhizal symbiosis |journal=Planta |volume=221 |issue=2 |pages=184–96 |year=2005 |pmid=15871030}}</ref>
 
However, not all interactions between species involve conflict.<ref>{{cite journal |author=Sachs J |title=Cooperation within and among species |journal=J. Evol. Biol. |volume=19 |issue=5 |pages=1415–8; discussion 1426–36 |year=2006 |pmid=16910971}}<br />*{{cite journal |author=Nowak M |title=Five rules for the evolution of cooperation |journal=Science |volume=314 |issue=5805 |pages=1560–63 |year=2006 |pmid=17158317}}</ref> Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the [[Mycorrhiza|mycorrhizal fungi]] that grow on their roots and aid the plant in absorbing nutrients from the soil.<ref>{{cite journal |author=Paszkowski U |title=Mutualism and parasitism: the yin and yang of plant symbioses |journal=Curr. Opin. Plant Biol. |volume=9 |issue=4 |pages=364–70 |year=2006 |pmid=16713732}}</ref> This is a [[Reciprocity (evolution)|reciprocal]] relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending [[signal transduction|signals]] that suppress the plant [[immune system]].<ref>{{cite journal |author=Hause B, Fester T |title=Molecular and cell biology of arbuscular mycorrhizal symbiosis |journal=Planta |volume=221 |issue=2 |pages=184–96 |year=2005 |pmid=15871030}}</ref>
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===Speciation===
 
===Speciation===
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{{details more|Speciation}}
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[[Image:Speciation modes edit.svg|right|thumb|300px|The four mechanisms of [[speciation]].]]
 
[[Image:Speciation modes edit.svg|right|thumb|300px|The four mechanisms of [[speciation]].]]
 
[[Speciation]] is the process where a species diverges into two or more descendant species.<ref name=Gavrilets>{{cite journal |author=Gavrilets S |title=Perspective: models of speciation: what have we learned in 40 years? |journal=Evolution |volume=57 |issue=10 |pages=2197–215 |year=2003 |pmid=14628909}}</ref> It has been observed multiple times under both controlled laboratory conditions and in nature.<ref>{{cite journal |author=Jiggins CD, Bridle JR |title=Speciation in the apple maggot fly: a blend of vintages? |journal=Trends Ecol. Evol. (Amst.) |volume=19 |issue=3 |pages=111–4 |year=2004 |pmid=16701238}}<br />*{{cite web|author=Boxhorn, J|date=1995|url=http://www.talkorigins.org/faqs/faq-speciation.html|title=Observed Instances of Speciation|publisher=The TalkOrigins Archive|accessdate=2007-05-10}}<br />*{{cite journal |author=Weinberg JR, Starczak VR, Jorg, D |title=Evidence for Rapid Speciation Following a Founder Event in the Laboratory |journal=Evolution |volume=46 |issue=4 |pages=1214–20 |year=1992 |doi=10.2307/2409766}}</ref> In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.<ref>{{cite journal|author=Hoskin CJ, Higgle M, McDonald KR, Moritz C |date=2005 |title=Reinforcement drives rapid allopatric speciation |journal=Nature |volume=437 |pages =1353–356|doi=10.1038/nature04004}}</ref>
 
[[Speciation]] is the process where a species diverges into two or more descendant species.<ref name=Gavrilets>{{cite journal |author=Gavrilets S |title=Perspective: models of speciation: what have we learned in 40 years? |journal=Evolution |volume=57 |issue=10 |pages=2197–215 |year=2003 |pmid=14628909}}</ref> It has been observed multiple times under both controlled laboratory conditions and in nature.<ref>{{cite journal |author=Jiggins CD, Bridle JR |title=Speciation in the apple maggot fly: a blend of vintages? |journal=Trends Ecol. Evol. (Amst.) |volume=19 |issue=3 |pages=111–4 |year=2004 |pmid=16701238}}<br />*{{cite web|author=Boxhorn, J|date=1995|url=http://www.talkorigins.org/faqs/faq-speciation.html|title=Observed Instances of Speciation|publisher=The TalkOrigins Archive|accessdate=2007-05-10}}<br />*{{cite journal |author=Weinberg JR, Starczak VR, Jorg, D |title=Evidence for Rapid Speciation Following a Founder Event in the Laboratory |journal=Evolution |volume=46 |issue=4 |pages=1214–20 |year=1992 |doi=10.2307/2409766}}</ref> In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.<ref>{{cite journal|author=Hoskin CJ, Higgle M, McDonald KR, Moritz C |date=2005 |title=Reinforcement drives rapid allopatric speciation |journal=Nature |volume=437 |pages =1353–356|doi=10.1038/nature04004}}</ref>
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One type of sympatric speciation involves cross-breeding of two related species to produce a new [[hybrid]] species. This is not common in animals as animal hybrids are usually sterile, because during [[meiosis]] the [[homologous chromosome]]s from each parent, being from different species cannot successfully pair. It is more common in plants, however because plants often double their number of chromosomes, to form [[polyploidy|polyploids]]. This allows the chromosomes from each parental species to form a matching pair during meiosis, as each parent's chromosomes is represented by a pair already.<ref>Belderok, Bob & Hans Mesdag & Dingena A. Donner. (2000) ''Bread-Making Quality of Wheat''. Springer. p.3. ISBN 0-7923-6383-3.<br />*Hancock, James F. (2004) ''Planti Evolution and the Origin of Crop Species''. CABI Publishing. ISBN 0-85199-685-X.</ref> An example of such a speciation event is when the plant species ''[[Arabidopsis thaliana]]'' and ''Arabidopsis arenosa'' cross-bred to give the new species ''Arabidopsis suecica''.<ref>{{cite journal |author=Jakobsson M, Hagenblad J, Tavaré S, ''et al'' |title=A unique recent origin of the allotetraploid species Arabidopsis suecica: Evidence from nuclear DNA markers |journal=Mol. Biol. Evol. |volume=23 |issue=6 |pages=1217–31 |year=2006 |pmid=16549398}}</ref> This happened about 20,000 years ago,<ref>{{cite journal |author=Säll T, Jakobsson M, Lind-Halldén C, Halldén C |title=Chloroplast DNA indicates a single origin of the allotetraploid Arabidopsis suecica |journal=J. Evol. Biol. |volume=16 |issue=5 |pages=1019–29 |year=2003 |pmid=14635917}}</ref> and the speciation process has been repeated in the laboratory, which allows the study of the genetic mechanisms involved in this process.<ref>{{cite journal |author=Bomblies K, Weigel D |title=Arabidopsis-a model genus for speciation |journal=Curr Opin Genet Dev |volume=17 |issue=6 |pages=500-504 |year=2007 |pmid=18006296}}</ref> Indeed, chromosome doubling within a species may be a common cause of reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.<ref name=Semon/>
 
One type of sympatric speciation involves cross-breeding of two related species to produce a new [[hybrid]] species. This is not common in animals as animal hybrids are usually sterile, because during [[meiosis]] the [[homologous chromosome]]s from each parent, being from different species cannot successfully pair. It is more common in plants, however because plants often double their number of chromosomes, to form [[polyploidy|polyploids]]. This allows the chromosomes from each parental species to form a matching pair during meiosis, as each parent's chromosomes is represented by a pair already.<ref>Belderok, Bob & Hans Mesdag & Dingena A. Donner. (2000) ''Bread-Making Quality of Wheat''. Springer. p.3. ISBN 0-7923-6383-3.<br />*Hancock, James F. (2004) ''Planti Evolution and the Origin of Crop Species''. CABI Publishing. ISBN 0-85199-685-X.</ref> An example of such a speciation event is when the plant species ''[[Arabidopsis thaliana]]'' and ''Arabidopsis arenosa'' cross-bred to give the new species ''Arabidopsis suecica''.<ref>{{cite journal |author=Jakobsson M, Hagenblad J, Tavaré S, ''et al'' |title=A unique recent origin of the allotetraploid species Arabidopsis suecica: Evidence from nuclear DNA markers |journal=Mol. Biol. Evol. |volume=23 |issue=6 |pages=1217–31 |year=2006 |pmid=16549398}}</ref> This happened about 20,000 years ago,<ref>{{cite journal |author=Säll T, Jakobsson M, Lind-Halldén C, Halldén C |title=Chloroplast DNA indicates a single origin of the allotetraploid Arabidopsis suecica |journal=J. Evol. Biol. |volume=16 |issue=5 |pages=1019–29 |year=2003 |pmid=14635917}}</ref> and the speciation process has been repeated in the laboratory, which allows the study of the genetic mechanisms involved in this process.<ref>{{cite journal |author=Bomblies K, Weigel D |title=Arabidopsis-a model genus for speciation |journal=Curr Opin Genet Dev |volume=17 |issue=6 |pages=500-504 |year=2007 |pmid=18006296}}</ref> Indeed, chromosome doubling within a species may be a common cause of reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.<ref name=Semon/>
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Speciation events are important in the theory of [[punctuated equilibrium]], which accounts for the pattern in the fossil record of short "bursts" of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged.<ref name=pe1972>Niles Eldredge and Stephen Jay Gould, 1972. [http://www.blackwellpublishing.com/ridley/classictexts/eldredge.asp "Punctuated equilibria: an alternative to phyletic gradualism"] In T.J.M. Schopf, ed., ''Models in Paleobiology''. San Francisco: Freeman Cooper. pp. 82-115. Reprinted in N. Eldredge ''Time frames''. Princeton: Princeton Univ. Press. 1985</ref> In this theory, speciation and rapid evolution are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population, and the organisms undergoing speciation and rapid evolution are found in small populations or geographically-restricted habitats, and therefore rarely being preserved as fossils.<ref>{{cite journal |author=Gould SJ |title=Tempo and mode in the macroevolutionary reconstruction of Darwinism |url=http://www.pnas.org/cgi/reprint/91/15/6764 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=91 |issue=15 |pages=6764–71 |year=1994 |pmid=8041695}}</ref>
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Speciation events are important in the theory of [[punctuated equilibrium]], which accounts for the pattern in the fossil record of short "bursts" of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged.<ref name=pe1972>Niles Eldredge and Stephen Jay Gould, 1972. [http://www.blackwellpublishing.com/ridley/classictexts/eldredge.asp "Punctuated equilibria: an alternative to phyletic gradualism"] In T.J.M. Schopf, ed., ''Models in Paleobiology''. San Francisco: Freeman Cooper. pp. 82-115. Reprinted in N. Eldredge ''Time frames''. Princeton: Princeton Univ. Press. 1985</ref> In this theory, speciation and rapid evolution are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population, and the organisms undergoing speciation and rapid evolution are found in small populations or geographically-restricted habitats, and therefore rarely being preserved as fossils.<ref>{{cite journal |author=Gould SJ |title=Tempo and mode in the macroevolutionary reconstruction of Darwinism |url=http://www.pnas.org/cgi/reprint/91/15/6764]
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===Extinction===
 
===Extinction===
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{{details more|Extinction}}
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[[Image:Tarbosaurus museum Muenster.jpg|thumb|right|225px|A ''[[Tarbosaurus]]'' skeleton. Non-[[bird|avian]] [[dinosaur]]s died out in the [[Cretaceous–Tertiary extinction event]] at the end of the [[Cretaceous]] period.]]
 
[[Image:Tarbosaurus museum Muenster.jpg|thumb|right|225px|A ''[[Tarbosaurus]]'' skeleton. Non-[[bird|avian]] [[dinosaur]]s died out in the [[Cretaceous–Tertiary extinction event]] at the end of the [[Cretaceous]] period.]]
 
[[Extinction]] is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation, and disappear through extinction.<ref>{{cite journal |author=Benton MJ |title=Diversification and extinction in the history of life |journal=Science |volume=268 |issue=5207 |pages=52–58 |year=1995 |pmid=7701342}}</ref> Indeed, virtually all animal and plant species that have lived on earth are now extinct.<ref>{{cite journal |author=Raup DM |title=Biological extinction in earth history |journal=Science |volume=231 |issue= |pages=1528–33 |year=1986 |pmid=11542058}}</ref> These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass [[extinction event]]s.<ref name=Raup>{{cite journal |author=Raup DM |title=The role of extinction in evolution |url=http://www.pnas.org/cgi/reprint/91/15/6758.pdf |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=91 |issue=15 |pages=6758–63 |year=1994 |pmid=8041694}}</ref> The [[Cretaceous–Tertiary extinction event]], during which the dinosaurs went extinct, is the most well-known, but the earlier [[Permian-Triassic extinction event]] was even more severe, with approximately 96 percent of species driven to extinction.<ref name=Raup/> The Holocene extinction event is an ongoing mass extinction associated with humanity's expansion across the globe over the past few thousand years. Present-day extinction rates are 100-1000 times greater than the background rate, and up to 30 percent of species may be extinct by the mid 21st century.<ref>{{cite journal |author=Novacek MJ, Cleland EE |title=The current biodiversity extinction event: scenarios for mitigation and recovery |url=http://www.pnas.org/cgi/content/full/98/10/5466 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=98 |issue=10 |pages=5466–70 |year=2001 |pmid=11344295}}</ref> Human activities are now the primary cause of the ongoing extinction event;<ref>{{cite journal |author=Pimm S, Raven P, Peterson A, Sekercioglu CH, Ehrlich PR |title=Human impacts on the rates of recent, present, and future bird extinctions |url=http://www.pnas.org/cgi/content/full/103/29/10941 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=103 |issue=29 |pages=10941–6 |year=2006 |pmid=16829570}}<br />*{{cite journal |author=Barnosky AD, Koch PL, Feranec RS, Wing SL, Shabel AB |title=Assessing the causes of late Pleistocene extinctions on the continents |journal=Science |volume=306 |issue=5693 |pages=70–05 |year=2004 |pmid=15459379}}</ref> [[global warming]] may further accelerate it in the future.<ref>{{cite journal |author=Lewis OT |title=Climate change, species-area curves and the extinction crisis |url=http://www.journals.royalsoc.ac.uk/content/711761513317h856/fulltext.pdf |journal=Philos. Trans. R. Soc. Lond., B, Biol. Sci. |volume=361 |issue=1465 |pages=163–71 |year=2006 |pmid=16553315}}</ref>
 
[[Extinction]] is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation, and disappear through extinction.<ref>{{cite journal |author=Benton MJ |title=Diversification and extinction in the history of life |journal=Science |volume=268 |issue=5207 |pages=52–58 |year=1995 |pmid=7701342}}</ref> Indeed, virtually all animal and plant species that have lived on earth are now extinct.<ref>{{cite journal |author=Raup DM |title=Biological extinction in earth history |journal=Science |volume=231 |issue= |pages=1528–33 |year=1986 |pmid=11542058}}</ref> These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass [[extinction event]]s.<ref name=Raup>{{cite journal |author=Raup DM |title=The role of extinction in evolution |url=http://www.pnas.org/cgi/reprint/91/15/6758.pdf |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=91 |issue=15 |pages=6758–63 |year=1994 |pmid=8041694}}</ref> The [[Cretaceous–Tertiary extinction event]], during which the dinosaurs went extinct, is the most well-known, but the earlier [[Permian-Triassic extinction event]] was even more severe, with approximately 96 percent of species driven to extinction.<ref name=Raup/> The Holocene extinction event is an ongoing mass extinction associated with humanity's expansion across the globe over the past few thousand years. Present-day extinction rates are 100-1000 times greater than the background rate, and up to 30 percent of species may be extinct by the mid 21st century.<ref>{{cite journal |author=Novacek MJ, Cleland EE |title=The current biodiversity extinction event: scenarios for mitigation and recovery |url=http://www.pnas.org/cgi/content/full/98/10/5466 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=98 |issue=10 |pages=5466–70 |year=2001 |pmid=11344295}}</ref> Human activities are now the primary cause of the ongoing extinction event;<ref>{{cite journal |author=Pimm S, Raven P, Peterson A, Sekercioglu CH, Ehrlich PR |title=Human impacts on the rates of recent, present, and future bird extinctions |url=http://www.pnas.org/cgi/content/full/103/29/10941 |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=103 |issue=29 |pages=10941–6 |year=2006 |pmid=16829570}}<br />*{{cite journal |author=Barnosky AD, Koch PL, Feranec RS, Wing SL, Shabel AB |title=Assessing the causes of late Pleistocene extinctions on the continents |journal=Science |volume=306 |issue=5693 |pages=70–05 |year=2004 |pmid=15459379}}</ref> [[global warming]] may further accelerate it in the future.<ref>{{cite journal |author=Lewis OT |title=Climate change, species-area curves and the extinction crisis |url=http://www.journals.royalsoc.ac.uk/content/711761513317h856/fulltext.pdf |journal=Philos. Trans. R. Soc. Lond., B, Biol. Sci. |volume=361 |issue=1465 |pages=163–71 |year=2006 |pmid=16553315}}</ref>
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==Evolutionary history of life==
 
==Evolutionary history of life==
−
{{Main|Evolutionary history of life}}
+
===Origin of life===
   −
===Origin of life===
  −
{{details more|Origin of life|RNA world hypothesis}}
   
The origin of [[life]] is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens, does not depend on understanding exactly how life began.<ref>{{Cite web |last=Isaak |first=Mark |year=2005 |title=Claim CB090: Evolution without abiogenesis |publisher=[[TalkOrigins Archive]] |url=http://www.talkorigins.org/indexcc/CB/CB090.html |accessdate=2007-05-13}}</ref> The current [[scientific consensus]] is that the complex [[biochemistry]] that makes up life came from simpler chemical reactions, but it is unclear how this occurred.<ref>{{cite journal |author=Peretó J |title=Controversies on the origin of life |url=http://www.im.microbios.org/0801/0801023.pdf |journal=Int. Microbiol. |volume=8 |issue=1 |pages=23&ndash;31 |year=2005 |pmid=15906258}}</ref> Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any [[last universal ancestor|last universal common ancestor]] or ancestral gene pool.<ref>{{cite journal |author=Luisi PL, Ferri F, Stano P |title=Approaches to semi-synthetic minimal cells: a review |journal=Naturwissenschaften |volume=93 |issue=1 |pages=1&ndash;13 |year=2006 |pmid=16292523}}</ref><ref>{{cite journal |author=Trevors JT, Abel DL |title=Chance and necessity do not explain the origin of life |journal=Cell Biol. Int. |volume=28 |issue=11 |pages=729&ndash;39 |year=2004 |pmid=15563395}}{{cite journal |author=Forterre P, Benachenhou-Lahfa N, Confalonieri F, Duguet M, Elie C, Labedan B |title=The nature of the last universal ancestor and the root of the tree of life, still open questions |journal=BioSystems |volume=28 |issue=1–3 |pages=15&ndash;32 |year=1992 |pmid=1337989}}</ref> Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as [[RNA]],<ref>{{cite journal |author=Joyce GF |title=The antiquity of RNA-based evolution |journal=Nature |volume=418 |issue=6894 |pages=214&ndash;21 |year=2002 |pmid=12110897}}</ref> and the assembly of simple cells.<ref>{{cite journal |author=Trevors JT, Psenner R |title=From self-assembly of life to present-day bacteria: a possible role for nanocells |journal=FEMS Microbiol. Rev. |volume=25 |issue=5 |pages=573&ndash;82 |year=2001 |pmid=11742692}}</ref>
 
The origin of [[life]] is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens, does not depend on understanding exactly how life began.<ref>{{Cite web |last=Isaak |first=Mark |year=2005 |title=Claim CB090: Evolution without abiogenesis |publisher=[[TalkOrigins Archive]] |url=http://www.talkorigins.org/indexcc/CB/CB090.html |accessdate=2007-05-13}}</ref> The current [[scientific consensus]] is that the complex [[biochemistry]] that makes up life came from simpler chemical reactions, but it is unclear how this occurred.<ref>{{cite journal |author=Peretó J |title=Controversies on the origin of life |url=http://www.im.microbios.org/0801/0801023.pdf |journal=Int. Microbiol. |volume=8 |issue=1 |pages=23&ndash;31 |year=2005 |pmid=15906258}}</ref> Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any [[last universal ancestor|last universal common ancestor]] or ancestral gene pool.<ref>{{cite journal |author=Luisi PL, Ferri F, Stano P |title=Approaches to semi-synthetic minimal cells: a review |journal=Naturwissenschaften |volume=93 |issue=1 |pages=1&ndash;13 |year=2006 |pmid=16292523}}</ref><ref>{{cite journal |author=Trevors JT, Abel DL |title=Chance and necessity do not explain the origin of life |journal=Cell Biol. Int. |volume=28 |issue=11 |pages=729&ndash;39 |year=2004 |pmid=15563395}}{{cite journal |author=Forterre P, Benachenhou-Lahfa N, Confalonieri F, Duguet M, Elie C, Labedan B |title=The nature of the last universal ancestor and the root of the tree of life, still open questions |journal=BioSystems |volume=28 |issue=1–3 |pages=15&ndash;32 |year=1992 |pmid=1337989}}</ref> Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as [[RNA]],<ref>{{cite journal |author=Joyce GF |title=The antiquity of RNA-based evolution |journal=Nature |volume=418 |issue=6894 |pages=214&ndash;21 |year=2002 |pmid=12110897}}</ref> and the assembly of simple cells.<ref>{{cite journal |author=Trevors JT, Psenner R |title=From self-assembly of life to present-day bacteria: a possible role for nanocells |journal=FEMS Microbiol. Rev. |volume=25 |issue=5 |pages=573&ndash;82 |year=2001 |pmid=11742692}}</ref>
    
===Common descent===
 
===Common descent===
−
{{details more|Evidence of common descent|Common descent|Homology (biology)}}
+
 
 
[[Image:Ape skeletons.png|right|320px|thumbnail|The [[ape|hominoids]] are descendants of a [[common descent|common ancestor]].]]
 
[[Image:Ape skeletons.png|right|320px|thumbnail|The [[ape|hominoids]] are descendants of a [[common descent|common ancestor]].]]
 
All [[organisms]] on [[Earth]] are descended from a common ancestor or ancestral gene pool.<ref>{{cite journal |author=Penny D, Poole A |title=The nature of the last universal common ancestor |journal=Curr. Opin. Genet. Dev. |volume=9 |issue=6 |pages=672&ndash;77 |year=1999 |pmid=10607605}}</ref> Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events.<ref>{{cite journal |author=Bapteste E, Walsh DA |title=Does the 'Ring of Life' ring true? |journal=Trends Microbiol. |volume=13 |issue=6 |pages=256&ndash;61 |year=2005 |pmid=15936656}}</ref> The [[common descent]] of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits, and finally, that organisms can be classified using these similarities into a hierarchy of nested groups.<ref name=Darwin/>
 
All [[organisms]] on [[Earth]] are descended from a common ancestor or ancestral gene pool.<ref>{{cite journal |author=Penny D, Poole A |title=The nature of the last universal common ancestor |journal=Curr. Opin. Genet. Dev. |volume=9 |issue=6 |pages=672&ndash;77 |year=1999 |pmid=10607605}}</ref> Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events.<ref>{{cite journal |author=Bapteste E, Walsh DA |title=Does the 'Ring of Life' ring true? |journal=Trends Microbiol. |volume=13 |issue=6 |pages=256&ndash;61 |year=2005 |pmid=15936656}}</ref> The [[common descent]] of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits, and finally, that organisms can be classified using these similarities into a hierarchy of nested groups.<ref name=Darwin/>
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===Evolution of life===
 
===Evolution of life===
−
{{details|Timeline of evolution}}
+
 
 
[[Image:Collapsed tree labels simplified.png|thumb|400px|right|[[Phylogenetic tree|Evolutionary tree]] showing the divergence of modern species from their common ancestor in the center.<ref name=Ciccarelli>{{cite journal |author=Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P |title=Toward automatic reconstruction of a highly resolved tree of life |journal=Science |volume=311 |issue=5765 |pages=1283&ndash;87 |year=2006 |pmid=16513982}}</ref> The three [[Domain (biology)|domains]] are colored, with [[bacteria]] blue, [[archaea]] green, and [[eukaryote]]s red.]]
 
[[Image:Collapsed tree labels simplified.png|thumb|400px|right|[[Phylogenetic tree|Evolutionary tree]] showing the divergence of modern species from their common ancestor in the center.<ref name=Ciccarelli>{{cite journal |author=Ciccarelli FD, Doerks T, von Mering C, Creevey CJ, Snel B, Bork P |title=Toward automatic reconstruction of a highly resolved tree of life |journal=Science |volume=311 |issue=5765 |pages=1283&ndash;87 |year=2006 |pmid=16513982}}</ref> The three [[Domain (biology)|domains]] are colored, with [[bacteria]] blue, [[archaea]] green, and [[eukaryote]]s red.]]
 
Despite the uncertainty on how life began, it is clear that [[prokaryote]]s were the first organisms to inhabit Earth,<ref name=Cavalier-Smith>{{cite journal |author=Cavalier-Smith T |title=Cell evolution and Earth history: stasis and revolution |url=http://www.journals.royalsoc.ac.uk/content/0164755512w92302/fulltext.pdf |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=969&ndash;1006 |year=2006 |pmid=16754610}}</ref> approximately 3&ndash;4 billion years ago.<ref>{{cite journal |author=Schopf J |title=Fossil evidence of Archaean life |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=869&ndash;85 |year=2006 |pmid=16754604}}<br />*{{cite journal |author=Altermann W, Kazmierczak J |title=Archean microfossils: a reappraisal of early life on Earth |journal=Res Microbiol |volume=154 |issue=9 |pages=611&ndash;17 |year=2003 |pmid=14596897}}</ref> No obvious changes in [[morphology (biology)|morphology]] or cellular organization occurred in these organisms over the next few billion years.<ref>{{cite journal |author=Schopf J |title=Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic. |url=http://www.pnas.org/cgi/reprint/91/15/6735 |journal=Proc Natl Acad Sci U S A |volume=91 |issue=15 |pages=6735&ndash;42 |year=1994 |pmid=8041691}}</ref>
 
Despite the uncertainty on how life began, it is clear that [[prokaryote]]s were the first organisms to inhabit Earth,<ref name=Cavalier-Smith>{{cite journal |author=Cavalier-Smith T |title=Cell evolution and Earth history: stasis and revolution |url=http://www.journals.royalsoc.ac.uk/content/0164755512w92302/fulltext.pdf |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=969&ndash;1006 |year=2006 |pmid=16754610}}</ref> approximately 3&ndash;4 billion years ago.<ref>{{cite journal |author=Schopf J |title=Fossil evidence of Archaean life |journal=Philos Trans R Soc Lond B Biol Sci |volume=361 |issue=1470 |pages=869&ndash;85 |year=2006 |pmid=16754604}}<br />*{{cite journal |author=Altermann W, Kazmierczak J |title=Archean microfossils: a reappraisal of early life on Earth |journal=Res Microbiol |volume=154 |issue=9 |pages=611&ndash;17 |year=2003 |pmid=14596897}}</ref> No obvious changes in [[morphology (biology)|morphology]] or cellular organization occurred in these organisms over the next few billion years.<ref>{{cite journal |author=Schopf J |title=Disparate rates, differing fates: tempo and mode of evolution changed from the Precambrian to the Phanerozoic. |url=http://www.pnas.org/cgi/reprint/91/15/6735 |journal=Proc Natl Acad Sci U S A |volume=91 |issue=15 |pages=6735&ndash;42 |year=1994 |pmid=8041691}}</ref>
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==History of evolutionary thought==
 
==History of evolutionary thought==
−
{{details|History of evolutionary thought}}
   
[[Image:Charles Darwin aged 51 crop.jpg |thumb|150px|[[Charles Darwin]] at age 51, just after publishing ''[[On the Origin of Species]]''.]]
 
[[Image:Charles Darwin aged 51 crop.jpg |thumb|150px|[[Charles Darwin]] at age 51, just after publishing ''[[On the Origin of Species]]''.]]
 
Evolutionary ideas such as [[common descent]] and the [[transmutation of species]] have existed since at least the 6th century BC, when they were expounded by the [[Greek philosophy|Greek philosopher]] [[Anaximander]].<ref>{{cite book|author=Wright, S|date=1984|title=Evolution and the Genetics of Populations, Volume 1: Genetic and Biometric Foundations|publisher=The University of Chicago Press|isbn=0-226-91038-5}}</ref> Evolutionary thought was further developed by other early thinkers, including the Greek philosopher [[Empedocles]], the [[History of Western philosophy|Roman philosopher]] [[Lucretius]], the [[Islamic science|Arab biologist]] [[Al-Jahiz]],<ref>{{cite journal |author=Zirkle C |title=Natural Selection before the "Origin of Species" |journal=Proceedings of the American Philosophical Society |volume=84 |issue=1 |pages=71&ndash;123 |year=1941}}</ref> the [[Early Islamic philosophy|Persian philosopher]] [[Ibn Miskawayh]], and the [[Brethren of Purity]].<ref>[[Muhammad Hamidullah]] and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad.</ref> Also in the Far East, the philosopher [[Zhuang Zi|Zhuangzi]] discussed a transformative power of species to adapt to their surroundings.<ref> "A Source Book In Chinese Philosophy", Chan, Wing-Tsit, p. 204, 1962. </ref>  As biological knowledge grew in the 18th century, a variety of such ideas developed, beginning with [[Pierre Louis Maupertuis|Pierre Maupertuis]] in 1745, and with contributions from natural philosophers such as [[Erasmus Darwin]] and [[Jean-Baptiste Lamarck]].<ref>{{cite book|author=Terrall, M|date=2002|title=The Man Who Flattened the Earth: Maupertuis and the Sciences in the Enlightenment|publisher=The University of Chicago Press|isbn=978-0226793610}}</ref> In 1858, [[Charles Darwin]] and [[Alfred Russel Wallace]] jointly proposed the theory of evolution by natural selection to the [[Linnean Society of London]] in [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection|separate papers]].<ref>{{cite journal|author=Wallace, A|coauthors= Darwin, C|url=http://darwin-online.org.uk/content/frameset?itemID=F350&viewtype=text&pageseq=1|title=On the Tendency of Species to form Varieties, and on the Perpetuation of Varieties and Species by Natural Means of Selection|journal=Journal of the Proceedings of the Linnean Society of London. Zoology|volume=3|date=1858|pages=53–62|accessdate=2007-05-13}}</ref> Shortly after, Darwin's publication of ''[[On the Origin of Species]]'' provided detailed support for the theory and led to increasingly wide acceptance of the occurrence of evolution.
 
Evolutionary ideas such as [[common descent]] and the [[transmutation of species]] have existed since at least the 6th century BC, when they were expounded by the [[Greek philosophy|Greek philosopher]] [[Anaximander]].<ref>{{cite book|author=Wright, S|date=1984|title=Evolution and the Genetics of Populations, Volume 1: Genetic and Biometric Foundations|publisher=The University of Chicago Press|isbn=0-226-91038-5}}</ref> Evolutionary thought was further developed by other early thinkers, including the Greek philosopher [[Empedocles]], the [[History of Western philosophy|Roman philosopher]] [[Lucretius]], the [[Islamic science|Arab biologist]] [[Al-Jahiz]],<ref>{{cite journal |author=Zirkle C |title=Natural Selection before the "Origin of Species" |journal=Proceedings of the American Philosophical Society |volume=84 |issue=1 |pages=71&ndash;123 |year=1941}}</ref> the [[Early Islamic philosophy|Persian philosopher]] [[Ibn Miskawayh]], and the [[Brethren of Purity]].<ref>[[Muhammad Hamidullah]] and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad.</ref> Also in the Far East, the philosopher [[Zhuang Zi|Zhuangzi]] discussed a transformative power of species to adapt to their surroundings.<ref> "A Source Book In Chinese Philosophy", Chan, Wing-Tsit, p. 204, 1962. </ref>  As biological knowledge grew in the 18th century, a variety of such ideas developed, beginning with [[Pierre Louis Maupertuis|Pierre Maupertuis]] in 1745, and with contributions from natural philosophers such as [[Erasmus Darwin]] and [[Jean-Baptiste Lamarck]].<ref>{{cite book|author=Terrall, M|date=2002|title=The Man Who Flattened the Earth: Maupertuis and the Sciences in the Enlightenment|publisher=The University of Chicago Press|isbn=978-0226793610}}</ref> In 1858, [[Charles Darwin]] and [[Alfred Russel Wallace]] jointly proposed the theory of evolution by natural selection to the [[Linnean Society of London]] in [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection|separate papers]].<ref>{{cite journal|author=Wallace, A|coauthors= Darwin, C|url=http://darwin-online.org.uk/content/frameset?itemID=F350&viewtype=text&pageseq=1|title=On the Tendency of Species to form Varieties, and on the Perpetuation of Varieties and Species by Natural Means of Selection|journal=Journal of the Proceedings of the Linnean Society of London. Zoology|volume=3|date=1858|pages=53–62|accessdate=2007-05-13}}</ref> Shortly after, Darwin's publication of ''[[On the Origin of Species]]'' provided detailed support for the theory and led to increasingly wide acceptance of the occurrence of evolution.
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==Social and cultural views==
 
==Social and cultural views==
−
{{details more|Social effect of evolutionary theory}}
+
 
 
[[Image:Darwin ape.jpg|right|150px|thumb|Caricature of [[Charles Darwin]] as a quadrupedal [[ape]], reflecting the cultural backlash against evolution.]]
 
[[Image:Darwin ape.jpg|right|150px|thumb|Caricature of [[Charles Darwin]] as a quadrupedal [[ape]], reflecting the cultural backlash against evolution.]]
 
Even before the publication of ''[[On the Origin of Species]]'', the idea that life had evolved was a source of debate and evolution is still a contentious concept. Debate has generally centered on the philosophical, social and religious implications of evolution, not on the science itself; the proposition that biological evolution occurs through the mechanism of natural selection is standard in the [[scientific literature]].<ref>For an overview of the philosophical, religious, and cosmological controversies, see: {{cite book|authorlink=Daniel Dennett|last=Dennett|first=D|title=[[Darwin's Dangerous Idea|Darwin's Dangerous Idea: Evolution and the Meanings of Life]]|publisher=Simon & Schuster|date=1995|isbn=978-0684824710}}<br />*For the scientific and social reception of evolution in the 19th and early 20th centuries, see: {{cite web | last = Johnston | first = Ian C. | title = History of Science: Origins of Evolutionary Theory | work = And Still We Evolve | publisher = Liberal Studies Department, Malaspina University College | url =http://www.mala.bc.ca/~johnstoi/darwin/sect3.htm| accessdate =2007-05-24}}<br />*{{cite book|authorlink=Peter J. Bowler|last=Bowler|first=PJ|title=Evolution: The History of an Idea, Third Edition, Completely Revised and Expanded|publisher=University of California Press|isbn=978-0520236936|date=2003}}<br />*{{cite journal |author=Zuckerkandl E |title=Intelligent design and biological complexity |journal=Gene |volume=385 |issue= |pages=2&ndash;18 |year=2006 |pmid=17011142}}</ref>
 
Even before the publication of ''[[On the Origin of Species]]'', the idea that life had evolved was a source of debate and evolution is still a contentious concept. Debate has generally centered on the philosophical, social and religious implications of evolution, not on the science itself; the proposition that biological evolution occurs through the mechanism of natural selection is standard in the [[scientific literature]].<ref>For an overview of the philosophical, religious, and cosmological controversies, see: {{cite book|authorlink=Daniel Dennett|last=Dennett|first=D|title=[[Darwin's Dangerous Idea|Darwin's Dangerous Idea: Evolution and the Meanings of Life]]|publisher=Simon & Schuster|date=1995|isbn=978-0684824710}}<br />*For the scientific and social reception of evolution in the 19th and early 20th centuries, see: {{cite web | last = Johnston | first = Ian C. | title = History of Science: Origins of Evolutionary Theory | work = And Still We Evolve | publisher = Liberal Studies Department, Malaspina University College | url =http://www.mala.bc.ca/~johnstoi/darwin/sect3.htm| accessdate =2007-05-24}}<br />*{{cite book|authorlink=Peter J. Bowler|last=Bowler|first=PJ|title=Evolution: The History of an Idea, Third Edition, Completely Revised and Expanded|publisher=University of California Press|isbn=978-0520236936|date=2003}}<br />*{{cite journal |author=Zuckerkandl E |title=Intelligent design and biological complexity |journal=Gene |volume=385 |issue= |pages=2&ndash;18 |year=2006 |pmid=17011142}}</ref>
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==Applications in technology==
 
==Applications in technology==
−
{{details more|Artificial selection|Evolutionary computation}}
      
A major technological application of evolution is [[artificial selection]], which is the intentional selection of certain traits in a population of organisms. Humans have used artificial selection for thousands of years in the [[domestication]] of plants and animals.<ref>{{cite journal |author=Doebley JF, Gaut BS, Smith BD |title=The molecular genetics of crop domestication |journal=Cell |volume=127 |issue=7 |pages=1309-21 |year=2006 |pmid=17190597}}</ref> More recently, such selection has become a vital part of [[genetic engineering]], with [[selectable marker]]s such as antibiotic resistance genes being used to manipulate DNA in [[molecular biology]].
 
A major technological application of evolution is [[artificial selection]], which is the intentional selection of certain traits in a population of organisms. Humans have used artificial selection for thousands of years in the [[domestication]] of plants and animals.<ref>{{cite journal |author=Doebley JF, Gaut BS, Smith BD |title=The molecular genetics of crop domestication |journal=Cell |volume=127 |issue=7 |pages=1309-21 |year=2006 |pmid=17190597}}</ref> More recently, such selection has become a vital part of [[genetic engineering]], with [[selectable marker]]s such as antibiotic resistance genes being used to manipulate DNA in [[molecular biology]].
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* {{cite book |author=Barton, N.H., Briggs, D.E.G., Eisen, J.A., Goldstein, D.B. and Patel, N.H. |title=Evolution |publisher=Cold Spring Harbor Laboratory Press |year=2007 |isbn=0-879-69684-2}}
 
* {{cite book |author=Barton, N.H., Briggs, D.E.G., Eisen, J.A., Goldstein, D.B. and Patel, N.H. |title=Evolution |publisher=Cold Spring Harbor Laboratory Press |year=2007 |isbn=0-879-69684-2}}
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==Outcomes==
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Evolution influences every aspect of the form and behavior of organisms. Most prominent are the specific behavioral and physical [[adaptation]]s that are the outcome of natural selection. These adaptations increase fitness by aiding activities such as finding food, avoiding predators or attracting mates. Organisms can also respond to selection by [[Co-operation (evolution)|co-operating]] with each other, usually by aiding their relatives or engaging in mutually-beneficial [[symbiosis|partnerships]]. In the longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that are unable to breed with one another.
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These outcomes of evolution are sometimes divided into [[macroevolution]], which is evolution that occurs at or above the level of species, such as [[speciation]], and [[microevolution]], which is smaller evolutionary changes, such as adaptations, within a species or population. In general, macroevolution is the outcome of long periods of microevolution. Thus, the distinction between micro- and macroevolution is not a fundamental one - the difference is simply the time involved. However, in macroevolution, the traits of the entire species are important. For instance, a large amount of variation among individuals allows a species to rapidly adapt to new habitats, lessening the chance of it going extinct, while a wide geographic range increases the chance of speciation, by making it more likely that part of the population will become isolated. In this sense, microevolution and macroevolution can sometimes be separate.
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A common misconception is that evolution is "progressive," but natural selection has no long-term goal and does not necessarily produce greater complexity. [http://www.sciam.com/askexpert_question.cfm?articleID=00071863-683B-1C72-9EB7809EC588F2D7]  Although [[evolution of complexity|complex species]] have evolved, this occurs as a side effect of the overall number of organisms increasing, and simple forms of life remain more common. For example, the overwhelming majority of species are microscopic [[prokaryote]]s, which form about half the world's biomass despite their small size, and constitute the vast majority of Earth's biodiversity. [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15590780#r6] Simple organisms therefore remain the dominant form of life on Earth, and complex life appears more diverse only because it is [[biased sample|more noticeable]].
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===Adaptation===
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Adaptations are structures or behaviors that enhance a specific function, causing organisms to become better at surviving and reproducing.  They are produced by a combination of the continuous production of small, random changes in traits, followed by natural selection of the variants best-suited for their environment.  This process can cause either the gain of a new feature, or the loss of an ancestral feature. An example that shows both types of change is bacterial adaptation to [[antibiotic]] selection, with mutations causing [[antibiotic resistance]] by either modifying the target of the drug, or removing the transporters that allow the drug into the cell. [http://www.jstage.jst.go.jp/article/mandi/46/6/46_391/_article/-char/en]  However, many traits that appear to be simple adaptations are in fact [[exaptation]]s: structures originally adapted for one function, but which coincidentally became somewhat useful for some other function in the process.  One example is the African lizard ''Holapsis guentheri'', which developed an extremely flat head for hiding in crevices, as can be seen by looking at its near relatives. However, in this species, the head has become so flattened that it assists in gliding from tree to tree - an exaptation.
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As adaptation occurs through the gradual modification of existing structures, structures with similar internal organization may have very different functions in related organisms. This is the result of a single [[homology (biology)|ancestral structure]] being adapted to function in different ways. The bones within bat wings, for example, are structurally similar to both human hands and seal flippers, due to the common descent of these structures from an ancestor that also had five digits at the end of each forelimb. Other idiosyncratic anatomical features, such as [[sesamoid bone|bones in the wrist]] of the [[panda]] being formed into a false "thumb," indicate that an organism's evolutionary lineage can limit what adaptations are possible. [http://www.pnas.org/cgi/content/full/103/2/379]
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During adaption, some structures may lose their original function and become [[vestigial structure]]s.[http://links.jstor.org/sici?sici=0066-4162%281995%2926%3C249%3AVALONC%3E2.0.CO%3B2-2] Such structures may have little or no function in a current species, yet have a clear function in ancestral species, or other closely-related species. Examples include the non-functional remains of eyes in blind cave-dwelling fish, [http://jhered.oxfordjournals.org/cgi/content/full/96/3/185]  wings in flightless birds, and the presence of hip bones in whales and snakes. Examples of vestigial structures in humans include [[wisdom teeth]],[http://jada.ada.org/cgi/content/full/134/4/450]
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An area of current investigation in [[evolutionary developmental biology]] is the [[Developmental biology|developmental]] basis of adaptations and exaptations. This research addresses the origin and evolution of [[Embryogenesis|embryonic development]] and how modifications of development and developmental processes produce novel features. [http://www.ijdb.ehu.es/web/paper.php?doi=14756346] These studies have shown that evolution can alter development to create new structures, such as embryonic bone structures that develop into the jaw in other animals instead forming part of the middle ear in mammals. It is also possible for structures that have been lost in evolution to reappear due to changes in developmental genes, such as a mutation in [[chicken]]s causing embryos to grow teeth similar to those of [[crocodile]]s.
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===Co-evolution===
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Interactions between organisms can produce both conflict and co-operation. When the interaction is between pairs of species, such as a [[pathogen]] and a [[host (biology)|host]], or a [[predator]] and its prey, these species can develop matched sets of adaptations. Here, the evolution of one species causes adaptations in a second species. These changes in the second species then, in turn, cause new adaptations in the first species. This cycle of selection and response is called [[co-evolution]].  An example is the production of [[tetrodotoxin]] in the [[rough-skinned newt]] and the evolution of tetrodotoxin resistance in its predator, the [[Common Garter Snake|common garter snake]]. In this predator-prey pair, an [[evolutionary arms race]] has produced high levels of toxin in the newt and correspondingly high levels of resistance in the snake.
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===Co-operation===
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However, not all interactions between species involve conflict.  Many cases of mutually beneficial interactions have evolved. For instance, an extreme cooperation exists between plants and the [[Mycorrhiza|mycorrhizal fungi]] that grow on their roots and aid the plant in absorbing nutrients from the soil. This is a [[Reciprocity (evolution)|reciprocal]] relationship as the plants provide the fungi with sugars from photosynthesis. Here, the fungi actually grow inside plant cells, allowing them to exchange nutrients with their hosts, while sending [[signal transduction|signals]] that suppress the plant [[immune system]].
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Coalitions between organisms of the same species have also evolved. An extreme case is the [[Eusociality]] found in [[social insect]]s, such as [[bee]]s, [[termite]]s and [[ant]]s, where sterile insects feed and guard the small number of organisms in a [[Colony (biology)|colony]] that are able to reproduce. On an even smaller scale, the [[somatic cell]]s that make up the body of an animal are limited in their capacity to reproduce in order to maintain a stable organism which then supports a small number of the animal's [[germ cell]]s to produce offspring. Here, somatic cells respond to specific signals that instruct them to either [[growth factor|grow]] or [[Apoptosis|kill themselves]]. If cells ignore these signals and attempt to multiply inappropriately, their uncontrolled growth causes [[cancer]].<ref name=Bertram/>
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These examples of cooperation within species are thought to have evolved through the process of [[kin selection]], which is where one organism acts to help raise a relative's offspring. [http://www.pnas.org/cgi/content/full/104/23/9736] This activity is selected for because if the ''helping'' individual contains alleles which promote the helping activity, it is likely that its kin will ''also'' contain these alleles and thus those alleles will be passed on. Other processes that may promote cooperation include [[group selection]], where cooperation provides benefits to a group of organisms. [http://www.pnas.org/cgi/content/full/102/38/13367]
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===Speciation===
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[[Speciation]] is the process where a species diverges into two or more descendant species. It has been observed multiple times under both controlled laboratory conditions and in nature. [http://www.talkorigins.org/faqs/faq-speciation.html]  In sexually-reproducing organisms, speciation results from reproductive isolation followed by genealogical divergence. There are four mechanisms for speciation. The most common in animals is [[allopatric speciation]], which occurs in populations initially isolated geographically, such as by [[habitat fragmentation]] or migration. As selection and drift act independently in isolated populations, separation will eventually produce organisms that cannot interbreed.
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The second mechanism of speciation is [[peripatric speciation]], which occurs when small populations of organisms become isolated in a new environment. This differs from allopatric speciation in that the isolated populations are numerically much smaller than the parental population. Here, the [[founder effect]] causes rapid speciation through both rapid genetic drift and selection on a small gene pool.<ref>{{cite journal |author=Templeton AR |title=The theory of speciation via the founder principle |url=http://www.genetics.org/cgi/reprint/94/4/1011 |journal=Genetics |volume=94 |issue=4 |pages=1011&ndash;38 |year=1980 |pmid=6777243}}</ref>
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The third mechanism of speciation is [[parapatric speciation]]. This is similar to peripatric speciation in that a small population enters a new habitat, but differs in that there is no physical separation between these two populations. Instead, speciation results from the evolution of mechanisms that reduce gene flow between the two populations. Generally this occurs when there has been a drastic change in the environment within the parental species' habitat. One example is the grass ''[[Anthoxanthum|Anthoxanthum odoratum]]'', which can undergo parapatric speciation in response to localized metal pollution from mines. [http://www.nature.com/hdy/journal/v97/n1/full/6800835a.html] Here, plants evolve that have resistance to high levels of metals in the soil. Selection against interbreeding with the metal-sensitive parental population produces a change in flowering time of the metal-resistant plants, causing reproductive isolation. Selection against hybrids between the two populations may cause ''reinforcement'', which is the evolution of traits that promote mating within a species, as well as [[character displacement]], which is when two species become more distinct in appearance.
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Finally, in [[sympatric speciation]] species diverge without geographic isolation or changes in habitat. This form is rare since even a small amount of [[gene flow]] may remove genetic differences between parts of a population. Generally, sympatric speciation in animals requires the evolution of both [[Polymorphism (biology)|genetic differences]] and [[assortative mating|non-random mating]], to allow reproductive isolation to evolve.
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One type of sympatric speciation involves cross-breeding of two related species to produce a new [[hybrid]] species. This is not common in animals as animal hybrids are usually sterile, because during [[meiosis]] the [[homologous chromosome]]s from each parent, being from different species cannot successfully pair. It is more common in plants, however because plants often double their number of chromosomes, to form [[polyploidy|polyploids]]. This allows the chromosomes from each parental species to form a matching pair during meiosis, as each parent's chromosomes is represented by a pair already. ISBN 0-7923-6383-3.  ISBN 0-85199-685-X.
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Indeed, chromosome doubling can itself cause reproductive isolation, as half the doubled chromosomes will be unmatched when breeding with undoubled organisms.
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Speciation events are important in the theory of [[punctuated equilibrium]], which accounts for the pattern in the fossil record of short "bursts" of evolution interspersed with relatively long periods of stasis, where species remain relatively unchanged. In this theory, speciation and rapid evolution are linked, with natural selection and genetic drift acting most strongly on organisms undergoing speciation in novel habitats or small populations. As a result, the periods of stasis in the fossil record correspond to the parental population, and the organisms undergoing speciation and rapid evolution are found in small populations or geographically-restricted habitats, and therefore rarely being preserved as fossils. [http://www.pnas.org/cgi/reprint/91/15/6764]
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===Extinction===
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[[Extinction]] is the disappearance of an entire species. Extinction is not an unusual event, as species regularly appear through speciation, and disappear through extinction. Virtually all animal and plant species that have lived on earth are now extinct.  These extinctions have happened continuously throughout the history of life, although the rate of extinction spikes in occasional mass [[extinction event]]s. [http://www.pnas.org/cgi/reprint/91/15/6758.pdf] The [[Cretaceous-Tertiary extinction event]], during which the dinosaurs went extinct, is the most well-known, but the earlier [[Permian-Triassic extinction event]] was even more severe, with approximately 96 percent of species driven to extinction. The Holocene extinction event is an ongoing mass extinction associated with humanity's expansion across the globe over the past few thousand years. Present-day extinction rates are 100-1000 times greater than the background rate, and up to 30 percent of species may be extinct by the mid 21st century. [http://www.pnas.org/cgi/content/full/98/10/5466] Human activities are now the primary cause of the ongoing extinction event; [http://www.pnas.org/cgi/content/full/103/29/10941]  [[global warming]] may further accelerate it in the future. [www.journals.royalsoc.ac.uk/content/711761513317h856/fulltext.pdf]
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The role of extinction in evolution depends on which type is considered. The causes of the continuous "low-level" extinction events, which form the majority of extinctions, are not well understood and may be the result of competition between species for shared resources. If competition from other species does alter the probability that a species will become extinct, this could produce [[Unit of selection#Species selection and selection at higher taxonomic levels|species selection]] as a level of natural selection.  The intermittent mass extinctions are also important, but instead of acting as a selective force, they drastically reduce diversity in a nonspecific manner and promote bursts of [[adaptive radiation|rapid evolution]] and speciation in survivors.
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==Evolutionary history of life==
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===Origin of life===
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The origin of [[life]] is a necessary precursor for biological evolution, but understanding that evolution occurred once organisms appeared and investigating how this happens, does not depend on understanding exactly how life began. [http://www.talkorigins.org/indexcc/CB/CB090.html] Accessed 13 May 2007. The current [[scientific consensus]] is that the complex [[biochemistry]] that makes up life came from simpler chemical reactions, but it is unclear how this occurred. [http://www.im.microbios.org/0801/0801023.pdf]  Not much is certain about the earliest developments in life, the structure of the first living things, or the identity and nature of any [[last universal ancestor|last universal common ancestor]] or ancestral gene pool.  Consequently, there is no scientific consensus on how life began, but proposals include self-replicating molecules such as [[RNA]],  and the assembly of simple cells.
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===Common descent===
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All [[organisms]] on [[Earth]] are descended from a common ancestor or ancestral gene pool.  Current species are a stage in the process of evolution, with their diversity the product of a long series of speciation and extinction events.  The [[common descent]] of organisms was first deduced from four simple facts about organisms: First, they have geographic distributions that cannot be explained by local adaptation. Second, the diversity of life is not a set of completely unique organisms, but organisms that share morphological similarities. Third, vestigial traits with no clear purpose resemble functional ancestral traits, and finally, that organisms can be classified using these similarities into a hierarchy of nested groups.
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Past species have also left records of their evolutionary history. [[Fossil]]s, along with the comparative anatomy of present-day organisms, constitute the morphological, or anatomical, record. By comparing the anatomies of both modern and extinct species, paleontologists can infer the lineages of those species. However, this approach is most successful for organisms that had hard body parts, such as shells, bones or teeth. Further, as prokaryotes such as [[bacteria]] and [[archaea]] share a limited set of common morphologies, their fossils do not provide information on their ancestry.
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More recently, evidence for common descent has come from the study of [[biochemistry|biochemical]] similarities between organisms. For example, all living cells use the same [[nucleic acid]]s and [[amino acid]]s. The development of [[molecular genetics]] has revealed the record of evolution left in organisms' [[genome]]s: dating when species diverged through the [[molecular clock]] produced by mutations.  For example, these DNA sequence comparisons have revealed the close genetic similarity between humans and chimpanzees and shed light on when the common ancestor of these species existed.
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===Evolution of life===
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Despite the uncertainty on how life began, it is clear that [[prokaryote]]s were the first organisms to inhabit Earth,[http://www.journals.royalsoc.ac.uk/content/0164755512w92302/fulltext.pdf]  approximately 3 - 4 billion years ago.  No obvious changes in [[morphology (biology)|morphology]] or cellular organization occurred in these organisms over the next few billion years. [http://www.pnas.org/cgi/reprint/91/15/6735]
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The [[eukaryote]]s were the next major innovation in evolution. These came from ancient bacteria being engulfed by the ancestors of eukaryotic cells, in a cooperative association called [[endosymbiont|endosymbiosis]].  The engulfed bacteria and the host cell then underwent co-evolution, with the bacteria evolving into either [[mitochondrion|mitochondria]] or [[hydrogenosome]]s.  An independent second engulfment of [[cyanobacteria]]l-like organisms led to the formation of [[chloroplast]]s in algae and plants.
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The history of life was that of the unicellular eukaryotes, prokaryotes, and archaea until about a billion years ago when multicellular organisms began to appear in the oceans in the [[Ediacaran biota|Ediacaran]] period.
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Soon after the emergence of these first multicellular organisms, a remarkable amount of biological diversity appeared over approximately 10 million years, in an event called the [[Cambrian explosion]]. Here, the majority of [[phylum (biology)|types]] of modern animals evolved, as well as unique lineages that subsequently became extinct. Various triggers for the Cambrian explosion have been proposed, including the accumulation of [[oxygen]] in the [[atmosphere]] from [[photosynthesis]]. [http://www.ijdb.ehu.es/web/paper.php?doi=14756327]  About 500 million years ago, [[plant]]s and [[fungus|fungi]] colonized the land, and were soon followed by [[arthropod]]s and other animals.  [[Amphibian]]s first appeared around 300 million years ago, followed by early [[amniotes]], then [[mammal]]s around 200 million years ago and [[bird]]s around 100 million years ago (both from "[[reptile]]"-like lineages). However, despite the evolution of these large animals, smaller organisms similar to the types that evolved early in this process continue to be highly successful and dominate the Earth, with the majority of both [[Biomass (ecology)|biomass]] and species being prokaryotes.<ref name=Schloss/>
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===History of evolutionary thought===
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Evolutionary ideas such as [[common descent]] and the [[transmutation of species]] have existed since at least the 6th century BC, when they were expounded by the [[Greek philosophy|Greek philosopher]] [[Anaximander]]. ISBN 0-226-91038-5 Evolutionary thought was further developed by other early thinkers, including the Greek philosopher [[Empedocles]], the [[History of Western philosophy|Roman philosopher]] [[Lucretius]], the [[Islamic science|Arab biologist]] [[Al-Jahiz]], the [[Early Islamic philosophy|Persian philosopher]] [[Ibn Miskawayh]], and the [[Brethren of Purity]]. [[Muhammad Hamidullah]] and Afzal Iqbal (1993), ''The Emergence of Islam: Lectures on the Development of Islamic World-view, Intellectual Tradition and Polity'', p. 143-144. Islamic Research Institute, Islamabad. As biological knowledge grew in the 18th century, a variety of such ideas developed, beginning with [[Pierre Louis Maupertuis|Pierre Maupertuis]] in 1745, and with contributions from natural philosophers such as [[Erasmus Darwin]] and [[Jean-Baptiste Lamarck]].The Man Who Flattened the Earth: Maupertuis and the Sciences in the Enlightenment, ISBN 978-0226793610.  In 1858, [[Charles Darwin]] and [[Alfred Russel Wallace]] jointly proposed the theory of evolution by natural selection to the [[Linnean Society of London]] in [[On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection|separate papers]]. Shortly after, Darwin's publication of ''[[The Origin of Species]]'' provided detailed support for the theory and led to increasingly wide acceptance of the occurrence of evolution.
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Nonetheless, Darwin's specific ideas about evolution, such as [[gradualism]] and the mechanisms of natural selection, were strongly contested at first. [[Lamarckism|Lamarckists]] argued that [[transmutation of species]] occurred as parents [[inheritance of acquired characters|passed on adaptations acquired]] during their lifetimes. Eventually, when experiments failed to support it, this idea was abandoned in favor of Darwinism., A History of the Life Sciences, Third Edition, Revised and Expanded, ISBN 978-0824708245. More significantly, Darwin could not account for how traits were passed down from generation to generation. A mechanism was provided in 1865 by [[Gregor Mendel]], who found that traits were [[Mendelian inheritance|inherited]] in a predictable manner. When Mendel's work was rediscovered in 1900, disagreements over the rate of evolution predicted by early geneticists and [[biostatistics|biometricians]] led to a rift between the Mendelian and Darwinian models of evolution.
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This contradiction was reconciled in the 1930s by biologists such as [[Ronald Fisher]]. The end result was a combination of evolution by natural selection and Mendelian inheritance, the [[modern evolutionary synthesis]].The Mendelian Revolution: The Emergence of Hereditarian Concepts in Modern Science and Society, ISBN 978-0801838880.  In the 1940s, the identification of [[DNA]] as the genetic material by [[Oswald Avery]] and colleagues and the subsequent publication of the structure of DNA by [[James D. Watson|James Watson]] and [[Francis Crick]] in 1953, demonstrated the physical basis for inheritance. Since then, [[genetics]] and [[molecular biology]] have become core parts of [[evolutionary biology]] and have revolutionized the field of [[phylogenetics]].
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In its early history, evolutionary biology primarily drew in scientists from traditional taxonomically-oriented disciplines, whose specialist training in particular organisms addressed general questions in evolution. As evolutionary biology expanded as an academic discipline, particularly after the development of the modern evolutionary synthesis, it began to draw more widely from the biological sciences.  Currently the study of evolutionary biology involves scientists from fields as diverse as [[biochemistry]], [[ecology]], [[genetics]] and [[physiology]], and evolutionary concepts are used in even more distant disciplines such as [[psychology]], [[medicine]], [[philosophy]] and [[computer science]].
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==Social and religious controversies==
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Even before the publication of ''[[The Origin of Species]]'', the idea that life had evolved was a source of controversy and evolution is still the subject of contention. Debate has generally centered on the philosophical, social and religious implications of evolution, not on the science itself; the proposition that biological evolution occurs through the mechanism of natural selection is completely uncontested in the [[scientific literature]]. For an overview of the philosophical, religious, and cosmological controversies, see: Darwin's Dangerous Idea: Evolution and the Meanings of Life]] ISBN 978-0684824710. For the scientific and social reception of evolution in the 19th and early 20th centuries, see: [http://www.mala.bc.ca/~johnstoi/darwin/sect3.htm] , Evolution: The History of an Idea, Third Edition, Completely Revised and Expanded, ISBN 978-0520236936
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As Darwin recognized early on, the most controversial aspect of evolutionary thought is its [[human evolution|application to humans]]. Specifically, some people object to the idea that humans arose through [[natural science|natural]] processes without supernatural intervention. Although [[Level of support for evolution#Support for evolution by religious bodies|many religions and denominations]] have reconciled their beliefs with evolution through [[theistic evolution|theological development]], several denominations contain [[creationism|creationists]] who object to evolution, as it contradicts their literal interpretation of [[origin belief]]s. [http://www.answersingenesis.org/home/area/re1/chapter1.asp] [http://www.answersingenesis.org/ Answers in Genesis] In some countries; notably the United States; these tensions between scientific and religious teachings have fueled the ongoing [[creation-evolution controversy|creation–evolution controversy]], a religious conflict focusing on [[politics of creationism|politics]] and [[creation and evolution in public education|public education]].  While other scientific fields such as [[physical cosmology|cosmology]]  and [[earth science]] also conflict with literal interpretations of many religious texts, evolutionary biology has borne the brunt of religious objection.
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Evolution has also attracted controversy because it has been used to support philosophical positions that promote [[discrimination]] and [[racism]]. For example, the [[eugenics|eugenic]] ideas of [[Francis Galton]] were developed into arguments that the human gene pool should be improved by [[selective breeding]] policies, including incentives for those considered "good stock" to reproduce, and the [[compulsory sterilization]], [[prenatal testing]], [[birth control]], and even [[Action T4|killing]], of those considered ''bad stock''., Kevles DJ, Eugenics and human rights [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=10445929] Another example of an extension of evolutionary theory that is now widely regarded as unwarranted is "[[Social Darwinism]]," a term given to the 19th century [[British Whig Party|Whig]] [[Malthusianism|Malthusian]] theory developed by [[Herbert Spencer]] into ideas about "[[survival of the fittest]]" in commerce and human societies as a whole, and by others into claims that [[social inequality]], racism, and [[imperialism]] were justified. On the history of eugenics and evolution, see In the Name of Eugenics: Genetics and the Uses of Human Heredity, Harvard University Press, ISBN 978-0674445574 However, contemporary scientists and philosophers consider these ideas to have been neither mandated by evolutionary theory nor supported by data. [[Charles Darwin|Darwin]] strongly disagreed with attempts by Herbert Spencer and others to extrapolate evolutionary ideas to all possible subjects; see Mary Midgley, The Myths we Live, Routledge|pages, ISBN 978-0415340779 Evolutionary ethics from Darwin to Moore
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==Uses in technology==
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A major technological application of the power of evolution is [[artificial selection]], which is the intentional selection of certain traits in a population of organisms. Humans have used artificial selection for thousands of years in the [[domestication]] of plants and animals. More recently, such selection has become a vital part of [[genetic engineering]], with [[selectable marker]]s such as antibiotic resistance genes being used to manipulate DNA in [[molecular biology]].
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As evolution can produce highly optimized processes and networks, it has many applications in [[computer science]]. Here, simulations of evolution using [[evolutionary algorithm]]s and [[artificial life]] started with the work of Nils Aall Barricelli in the 1960s, and was extended by [[Alex Fraser (scientist)|Alex Fraser]], who published a series of papers on simulation of [[artificial selection]]. [[Artificial evolution]] became a widely recognized optimization method as a result of the work of [[Ingo Rechenberg]] in the 1960s and early 1970s, who used [[evolution strategies]] to solve complex engineering problems. [[Genetic algorithms]] in particular became popular through the writing of [[John Henry Holland|John Holland]]. Adaptation in Natural and Artificial Systems, University of Michigan Press, ISBN 0262581116 As academic interest grew, dramatic increases in the power of computers allowed practical applications. Evolution algorithms are now used to solve multi-dimensional problems more quickly than software produced by human designers, and also to optimize the design of systems.
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==Further reading==
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'''Introductory reading'''
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* {{cite book |author=Jones S |authorlink = Steve Jones [[Almost Like a Whale|Almost Like a Whale: The Origin of Species Updated]]. '' ''Darwin's Ghost'' 0-345-42277-5}}
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* Richard Dawkins, The Selfish Gene|The Selfish Gene: 30th Anniversary Edition, Oxford University Press, ISBN 0199291152
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* Brian Charlesworth, Evolution |publisher=Oxford University Press, ISBN 0-192-80251-8
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* Stephen Jay Gould, Wonderful Life: The Burgess Shale and the Nature of History]] ISBN 0-393-30700-X
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* Sean B. Carroll, Endless Forms Most Beautiful, ISBN 0-393-06016-0
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* Charles Sullivan, The Top 10 Myths about Evolution, ISBN 978-1-59102-479-8
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'''History of evolutionary thought'''
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* Evolution: The Remarkable History of a Scientific Theory, ISBN 0-679-64288-9
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* Carl Zimmer, Evolution: The Triumph of an Idea, ISBN 0-060-19906-7
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'''Advanced reading'''
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* Stephen Jay Gould, The Structure of Evolutionary Theory, Belknap Press, ISBN 0-674-00613-5
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* Douglas J. Futuyma, Evolution, ISBN 0-878-93187-2
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* Ernst Mayr, What Evolution Is,  ISBN 0-465-04426-3
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* Jerry Coyne, Speciation, ISBN 0-878-93089-2
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* John Maynard Smith, The Major Transitions in Evolution]] ISBN 0-198-50294-X}}
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==External links==
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'''General information'''
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* [http://www.becominghuman.org/] Becoming Human, The Documentary
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* [http://evolution.berkeley.edu/ Understanding Evolution from University of California, Berkeley]
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* [http://nationalacademies.org/evolution/ National Academies Evolution Resources]
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* [http://www.newscientist.com/channel/life/evolution Everything you wanted to know about evolution by ''New Scientist'']
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* [http://science.howstuffworks.com/evolution.htm/printable Howstuffworks.com — How Evolution Works]
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* [http://anthro.palomar.edu/synthetic/ Synthetic Theory Of Evolution: An Introduction to Modern Evolutionary Concepts and Theories]
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'''History of evolutionary thought'''
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* [http://darwin-online.org.uk The Complete Work of Charles Darwin Online]
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* [http://www.rationalrevolution.net/articles/understanding_evolution.htm Understanding Evolution: History, Theory, Evidence, and Implications]
      
[[Category: General Reference]]
 
[[Category: General Reference]]
 
[[Category: Biology]]
 
[[Category: Biology]]
 
[[Category: Philosophy]]
 
[[Category: Philosophy]]
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