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Wikilink orthogenesis in text. Remove it from See also. Also remove "common descent" which is already a section in the article |
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[[File:Evolsex-dia1a.svg|thumb|upright=1.15|This diagram illustrates the ''twofold cost of sex''. If each individual were to contribute to the same number of offspring (two), ''(a)'' the sexual population remains the same size each generation, where the ''(b)'' [[Asexual reproduction]] population doubles in size each generation.{{imagefact|date=December 2022}}]]
The two-fold cost of sex was first described by [[John Maynard Smith]].<ref name="maynard">{{harvnb|Maynard Smith|1978}}{{page needed|date=December 2014}}</ref> The first cost is that in sexually dimorphic species only one of the two sexes can bear young. This cost does not apply to hermaphroditic species, like most plants and many [[invertebrate]]s. The second cost is that any individual who reproduces sexually can only pass on 50% of its genes to any individual offspring, with even less passed on as each new generation passes.<ref name="ridley">{{harvnb|Ridley|2004|p=314}}</ref> Yet sexual reproduction is the more common means of reproduction among eukaryotes and multicellular organisms. The [[Red Queen hypothesis]] has been used to explain the significance of sexual reproduction as a means to enable continual evolution and adaptation in response to [[coevolution]] with other species in an ever-changing environment.<ref name="ridley" /><ref name="red">{{cite journal |last=Van Valen |first=Leigh |author-link=Leigh Van Valen |year=1973 |title=A New Evolutionary Law |url=https://dl.dropboxusercontent.com/u/18310184/evolutionary-theory/vol-01/Vol.1%2CNo.1%2C1-30%2CL.%20Van%20Valen%2C%20A%20new%20evolutionary%20law..pdf |journal=Evolutionary Theory |volume=1 |pages=1–30 |issn=0093-4755 |access-date=24 December 2014 |archive-url=https://web.archive.org/web/20141222094258/https://dl.dropboxusercontent.com/u/18310184/evolutionary-theory/vol-01/Vol.1%2CNo.1%2C1-30%2CL.%20Van%20Valen%2C%20A%20new%20evolutionary%20law..pdf |archive-date=22 December 2014}}</ref><ref name="parasite">{{cite journal |last1=Hamilton |first1=W. D. |author-link1=W. D. Hamilton |last2=Axelrod |first2=Robert |author-link2=Robert Axelrod (political scientist) |last3=Tanese |first3=Reiko |date=1 May 1990 |title=Sexual reproduction as an adaptation to resist parasites (a review) |journal=PNAS |volume=87 |issue=9 |pages=3566–3573 |bibcode=1990PNAS...87.3566H |doi=10.1073/pnas.87.9.3566 |issn=0027-8424 |pmid=2185476 |pmc=53943|doi-access=free }}</ref><ref name="Birdsell">{{harvnb|Birdsell|Wills|2003|pp=113–117}}</ref> Another hypothesis is that sexual reproduction is primarily an adaptation for promoting accurate recombinational repair of damage in germline DNA, and that increased diversity is a byproduct of this process that may sometimes be adaptively beneficial.<ref>Bernstein H, Byerly HC, Hopf FA, Michod RE. Genetic damage, mutation, and the evolution of sex. Science. 1985 Sep 20;229(4719):1277–81. {{doi|10.1126/science.3898363}}. PMID 3898363</ref><ref>Bernstein H, Hopf FA, Michod RE. The molecular basis of the evolution of sex. Adv Genet. 1987;24:323-70. {{doi|10.1016/s0065-2660(08)60012-7}}. PMID 3324702</ref>
=== Gene flow ===
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Evolution influences every aspect of the form and behaviour of organisms. Most prominent are the specific behavioural and physical adaptations 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)|cooperating]] with each other, usually by aiding their relatives or engaging in mutually beneficial [[symbiosis]]. In the longer term, evolution produces new species through splitting ancestral populations of organisms into new groups that cannot or will not interbreed. These outcomes of evolution are distinguished based on time scale as [[macroevolution]] versus microevolution. Macroevolution refers to evolution that occurs at or above the level of species, in particular speciation and extinction, whereas microevolution refers to smaller evolutionary changes within a species or population, in particular shifts in allele frequency and adaptation.<ref name="ScottEC">{{cite journal |last1=Scott |first1=Eugenie C. |author-link1=Eugenie Scott |last2=Matzke |first2=Nicholas J. |author-link2=Nick Matzke |date=15 May 2007 |title=Biological design in science classrooms |journal=PNAS |volume=104 |issue=Suppl. 1 |pages=8669–8676 |bibcode=2007PNAS..104.8669S |doi=10.1073/pnas.0701505104 |pmid=17494747 |pmc=1876445 |doi-access=free }}</ref> Macroevolution is the outcome of long periods of microevolution.<ref>{{cite journal |last1=Hendry |first1=Andrew Paul |last2=Kinnison |first2=Michael T. |s2cid=24485535 |date=November 2001 |title=An introduction to microevolution: rate, pattern, process |journal=Genetica |volume=112–113 |issue=1 |pages=1–8 |doi=10.1023/A:1013368628607 |issn=0016-6707 |pmid=11838760}}</ref> Thus, the distinction between micro- and macroevolution is not a fundamental one—the difference is simply the time involved.<ref>{{cite journal |last=Leroi |first=Armand M. |author-link=Armand Marie Leroi |date=March–April 2000 |title=The scale independence of evolution |journal=Evolution & Development |volume=2 |issue=2 |pages=67–77 |doi=10.1046/j.1525-142x.2000.00044.x |issn=1520-541X |pmid=11258392 |citeseerx=10.1.1.120.1020 |s2cid=17289010 }}</ref> However, in macroevolution, the traits of the entire species may be important. For instance, a large amount of variation among individuals allows a species to rapidly adapt to new [[habitat]]s, 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 might involve selection at different levels—with microevolution acting on genes and organisms, versus macroevolutionary processes such as [[species selection]] acting on entire species and affecting their rates of speciation and extinction.{{sfn|Gould|2002|pp=657–658}}<ref name="Gould_1994">{{cite journal |last=Gould |first=Stephen Jay |date=19 July 1994 |title=Tempo and mode in the macroevolutionary reconstruction of Darwinism |journal=PNAS |volume=91 |issue=15 |pages=6764–6771 |bibcode=1994PNAS...91.6764G |doi=10.1073/pnas.91.15.6764 |pmc=44281 |pmid=8041695|doi-access=free }}</ref><ref name="Jablonski2000">{{cite journal |last=Jablonski |first=David |author-link=David Jablonski |year=2000 |title=Micro- and macroevolution: scale and hierarchy in evolutionary biology and paleobiology |journal=[[Paleobiology (journal)|Paleobiology]] |volume=26 |issue=sp4 |pages=15–52 |doi=10.1666/0094-8373(2000)26[15:MAMSAH]2.0.CO;2 |s2cid=53451360}}</ref>
A common misconception is that evolution has goals, long-term plans, or an innate tendency for "progress", as expressed in beliefs such as [[orthogenesis]] and evolutionism; realistically, however, evolution has no long-term goal and does not necessarily produce greater complexity.<ref name="sciam_1998">{{cite journal |last=Dougherty |first=Michael J. |date=20 July 1998 |title=Is the human race evolving or devolving? |url=http://www.scientificamerican.com/article/is-the-human-race-evolvin/ |journal=Scientific American |issn=0036-8733 |access-date=11 September 2015 |url-status=live |archive-url=https://wayback.archive-it.org/all/20140506224205/http://www.scientificamerican.com/article/is-the-human-race-evolvin/ |archive-date=6 May 2014}}</ref><ref>{{cite web |url=http://www.talkorigins.org/indexcc/CB/CB932.html |title=Claim CB932: Evolution of degenerate forms |date=22 July 2003 |editor-last=Isaak |editor-first=Mark |website=[[TalkOrigins Archive]] |publisher=The TalkOrigins Foundation |location=Houston, Texas |access-date=19 December 2014 |url-status=live |archive-url=https://web.archive.org/web/20140823062949/http://www.talkorigins.org/indexcc/CB/CB932.html |archive-date=23 August 2014}}</ref><ref>{{harvnb|Lane|1996|p=61}}</ref> Although [[Evolution of biological complexity|complex species]] have evolved, they occur as a side effect of the overall number of organisms increasing, and simple forms of life still remain more common in the biosphere.<ref name="Carroll_2001">{{cite journal |last=Carroll |first=Sean B. |author-link=Sean B. Carroll |date=22 February 2001 |title=Chance and necessity: the evolution of morphological complexity and diversity |url=https://archive.org/details/sim_nature-uk_2001-02-22_409_6823/page/1102 |journal=Nature |volume=409 |issue=6823 |pages=1102–1109 |bibcode=2001Natur.409.1102C |doi=10.1038/35059227 |pmid=11234024 |s2cid=4319886 }}</ref> For example, the overwhelming majority of species are microscopic [[prokaryote]]s, which form about half the world's [[Biomass (ecology)|biomass]] despite their small size<ref>{{cite journal |last1=Whitman |first1=William B. |last2=Coleman |first2=David C. |last3=Wiebe |first3=William J. |date=9 June 1998 |title=Prokaryotes: The unseen majority |journal=PNAS |volume=95 |issue=12 |pages=6578–6583 |bibcode=1998PNAS...95.6578W |doi=10.1073/pnas.95.12.6578 |issn=0027-8424 |pmc=33863 |pmid=9618454|doi-access=free }}</ref> and constitute the vast majority of Earth's biodiversity.<ref name="Schloss">{{cite journal |last1=Schloss |first1=Patrick D. |last2=Handelsman |first2=Jo |author-link2=Jo Handelsman |date=December 2004 |title=Status of the Microbial Census |journal=[[Microbiology and Molecular Biology Reviews]] |volume=68 |issue=4 |pages=686–691 |doi=10.1128/MMBR.68.4.686-691.2004 |pmc=539005 |pmid=15590780}}</ref> Simple organisms have therefore been the dominant form of life on Earth throughout its history and continue to be the main form of life up to the present day, with complex life only appearing more diverse because it is [[Sampling bias|more noticeable]].<ref>{{cite journal |last=Nealson |first=Kenneth H. |s2cid=12289639 |date=January 1999 |title=Post-Viking microbiology: new approaches, new data, new insights |url=https://archive.org/details/sim_origins-of-life-and-evolution-of-biospheres_1999-01_29_1/page/73 |journal=[[Origins of Life and Evolution of Biospheres]] |volume=29 |issue=1 |pages=73–93 |doi=10.1023/A:1006515817767 |issn=0169-6149 |pmid=11536899|bibcode=1999OLEB...29...73N }}</ref> Indeed, the evolution of microorganisms is particularly important to evolutionary research since their rapid reproduction allows the study of [[experimental evolution]] and the observation of evolution and adaptation in real time.<ref name="Buckling">{{cite journal |last1=Buckling |first1=Angus |last2=MacLean |first2=R. Craig |last3=Brockhurst |first3=Michael A. |last4=Colegrave |first4=Nick |s2cid=205216404 |date=12 February 2009 |title=The Beagle in a bottle |url=https://archive.org/details/sim_nature-uk_2009-02-12_457_7231/page/824 |journal=Nature |volume=457 |issue=7231 |pages=824–829 |bibcode=2009Natur.457..824B |doi=10.1038/nature07892 |issn=0028-0836 |pmid=19212400}}</ref><ref>{{cite journal |last1=Elena |first1=Santiago F. |last2=Lenski |first2=Richard E. |author-link2=Richard Lenski |date=June 2003 |title=Evolution experiments with microorganisms: the dynamics and genetic bases of adaptation |journal=Nature Reviews Genetics |volume=4 |issue=6 |pages=457–469 |doi=10.1038/nrg1088 |issn=1471-0056 |pmid=12776215|s2cid=209727 }}</ref>
=== Adaptation ===
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* {{cite journal |last=Zuckerkandl |first=Emile |author-link=Emile Zuckerkandl |date=30 December 2006 |title=Intelligent design and biological complexity |journal=[[Gene (journal)|Gene]] |volume=385 |pages=2–18 |pmid=17011142 |doi=10.1016/j.gene.2006.03.025 |issn=0378-1119 |ref=none}}</ref>
While [[Level of support for evolution#Religious|various religions and denominations]] have reconciled their beliefs with evolution through concepts such as [[theistic evolution]], there are [[creationism|creationists]] who believe that evolution is contradicted by the [[creation myth
The teaching of evolution in American secondary school biology classes was uncommon in most of the first half of the 20th century. The [[Scopes Trial]] decision of 1925 caused the subject to become very rare in American secondary biology textbooks for a generation, but it was gradually re-introduced later and became legally protected with the 1968 ''[[Epperson v. Arkansas]]'' decision. Since then, the competing religious belief of creationism was legally disallowed in secondary school curricula in various decisions in the 1970s and 1980s, but it returned in [[Pseudoscience|pseudoscientific]] form as [[intelligent design]] (ID), to be excluded once again in the 2005 ''[[Kitzmiller v. Dover Area School District]]'' case.<ref name="BioScience">{{cite journal |last=Branch |first=Glenn |s2cid=86665329 |author-link=Glenn Branch |date=March 2007 |title=Understanding Creationism after ''Kitzmiller'' |url=https://archive.org/details/sim_bioscience_2007-03_57_3/page/278 |journal=[[BioScience]] |volume=57 |issue=3 |pages=278–284 |doi=10.1641/B570313 |issn=0006-3568|doi-access=free }}</ref> The debate over Darwin's ideas did not generate significant controversy in China.<ref name="jin2019">{{cite journal |author=Xiaoxing Jin |date=March 2019 |title=Translation and transmutation: the ''Origin of Species'' in China |journal=The British Journal for the History of Science |location=Cambridge |publisher=Cambridge University Press on behalf of The British Society for the History of Science |volume=52 |issue=1 |pages=117–141 |pmid=30587253 |doi=10.1017/S0007087418000808|s2cid=58605626 }}</ref>
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==See also==
* {{annotated link|Devolution (biology)}}
* [[Chronospecies]]
== References ==
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