Editing Mammal (section)

===Hybrids===
{{Main|Hybrid (biology)}}
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|footer=A true [[quagga]], 1870 (left) vs. a [[Quagga Project|bred-back quagga]], 2014 (right)
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Hybrids are offspring resulting from the breeding of two genetically distinct individuals, which usually will result in a high degree of heterozygosity, though hybrid and heterozygous are not synonymous. The deliberate or accidental hybridising of two or more species of closely related animals through captive breeding is a human activity which has been in existence for millennia and has grown for economic purposes.<ref>{{cite book | vauthors = Price E |year=2008 |title=Principles and applications of domestic animal behavior: an introductory text |publisher=Cambridge University Press |url={{Google books|plainurl=yes|id=Ww07sIWTYAAC|page=228}}|location=Sacramento |isbn=978-1-84593-398-2|oclc=226038028}}</ref> Hybrids between different subspecies within a species (such as between the [[Bengal tiger]] and [[Siberian tiger]]) are known as intra-specific hybrids. Hybrids between different species within the same genus (such as between lions and tigers) are known as interspecific hybrids or crosses. Hybrids between different genera (such as between sheep and goats) are known as intergeneric hybrids.<ref>{{cite book|url={{Google books |plainurl=yes |id=O3M4qfxtGhIC|page=13}} |location=Heidelberg | vauthors = Taupitz J, Weschka M |year=2009|title=Chimbrids – Chimeras and Hybrids in Comparative European and International Research |publisher=Springer |page=13 |isbn=978-3-540-93869-9 |oclc=495479133}}</ref> Natural hybrids will occur in [[hybrid zone]]s, where two populations of species within the same genera or species living in the same or adjacent areas will interbreed with each other. Some hybrids have been recognised as species, such as the [[red wolf]] (though this is controversial).<ref>{{cite journal |title=An account of the taxonomy of North American wolves from morphological and genetic analyses |year=2012 |journal=North American Fauna |volume=77 |page=2 |doi=10.3996/nafa.77.0001 |vauthors=Chambers SM, Fain SR, Fazio B, Amaral M |url=https://digital.library.unt.edu/ark:/67531/metadc700981/ |doi-access=free |access-date=12 October 2019 |archive-date=31 May 2021 |archive-url=https://web.archive.org/web/20210531050233/https://digital.library.unt.edu/ark:/67531/metadc700981/ |url-status=live }}</ref>

[[Artificial selection]], the deliberate [[selective breeding]] of domestic animals, is being used to [[breeding back|breed back]] [[Holocene extinction|recently extinct]] animals in an attempt to achieve an animal breed with a [[phenotype]] that resembles that extinct [[wildtype]] ancestor. A breeding-back (intraspecific) hybrid may be very similar to the extinct wildtype in appearance, ecological niche and to some extent genetics, but the initial [[gene pool]] of that wild type is lost forever with its [[extinction]]. As a result, bred-back breeds are at best vague look-alikes of extinct wildtypes, as [[Heck cattle]] are of the [[aurochs]].<ref name="vanVuure">{{cite book | vauthors = van Vuure T |title=Retracing the Aurochs – History, Morphology and Ecology of an extinct wild Ox |year=2005 |isbn=978-954-642-235-4 |publisher=Pensoft Publishers |oclc=940879282}}</ref>

[[Purebred]] wild species evolved to a specific ecology can be threatened with extinction<ref>{{cite journal | vauthors = Mooney HA, Cleland EE | title = The evolutionary impact of invasive species | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 98 | issue = 10 | pages = 5446–5451 | date = May 2001 | pmid = 11344292 | pmc = 33232 | doi = 10.1073/pnas.091093398 | bibcode = 2001PNAS...98.5446M | doi-access = free }}</ref> through the process of [[genetic pollution]], the uncontrolled hybridisation, [[introgression]] genetic swamping which leads to homogenisation or [[Fitness (biology)|out-competition]] from the [[heterosis|heterosic]] hybrid species.<ref>{{cite journal | vauthors = Le Roux JJ, Foxcroft LC, Herbst M, MacFadyen S | title = Genetic analysis shows low levels of hybridization between African wildcats (Felis silvestris lybica) and domestic cats (F. s. catus) in South Africa | journal = Ecology and Evolution | volume = 5 | issue = 2 | pages = 288–299 | date = January 2015 | pmid = 25691958 | pmc = 4314262 | doi = 10.1002/ece3.1275| bibcode = 2015EcoEv...5..288L }}</ref> When new populations are imported or selectively bred by people, or when habitat modification brings previously isolated species into contact, extinction in some species, especially rare varieties, is possible.<ref>{{cite book| vauthors = Wilson A |title= Australia's state of the forests report |page=107 |year=2003}}</ref> [[Interbreeding]] can swamp the rarer gene pool and create hybrids, depleting the purebred gene pool. For example, the endangered [[wild water buffalo]] is most threatened with extinction by genetic pollution from the [[Water buffalo|domestic water buffalo]]. Such extinctions are not always apparent from a [[morphology (biology)|morphological]] standpoint. Some degree of [[gene flow]] is a normal evolutionary process, nevertheless, hybridisation threatens the existence of rare species.<ref>{{cite journal |title= Extinction by Hybridization and Introgression | vauthors = Rhymer JM, Simberloff D |journal = Annual Review of Ecology and Systematics |date=November 1996 |volume= 27 | issue = 1 |pages= 83–109 |doi= 10.1146/annurev.ecolsys.27.1.83 | bibcode = 1996AnRES..27...83R }}</ref><ref>{{cite book | vauthors = Potts BM | veditors = Barbour RC, Hingston AB |year=2001 |title=Genetic pollution from farm forestry using eucalypt species and hybrids: a report for the RIRDC/L&WA/FWPRDC Joint Venture Agroforestry Program |publisher= Rural Industrial Research and Development Corporation of Australia|isbn= 978-0-642-58336-9|oclc=48794104}}</ref>