Editing Convergent evolution (section)

== Distinctions ==

===Cladistics===

{{Main|Cladistics}}

In cladistics, a homoplasy is a trait shared by two or more [[Taxon|taxa]] for any reason other than that they share a common ancestry. Taxa which do share ancestry are part of the same [[clade]]; cladistics seeks to arrange them according to their degree of relatedness to describe their [[phylogeny]]. Homoplastic traits caused by convergence are therefore, from the point of view of cladistics, confounding factors which could lead to an incorrect analysis.<ref>{{cite journal |last1=Chirat |first1=R. |last2=Moulton |first2=D. E. |last3=Goriely |first3=A. |doi=10.1073/pnas.1220443110 |title=Mechanical basis of morphogenesis and convergent evolution of spiny seashells |journal=Proceedings of the National Academy of Sciences |volume=110 |issue=15 |pages=6015–6020 |year=2013 |bibcode=2013PNAS..110.6015C |pmid=23530223 |pmc=3625336 |doi-access=free }}</ref><ref name="Lomolino et al">{{cite book |last1=Lomolino |first1=M. |author2=Riddle, B. |author3=Whittaker, R. |author4=Brown, J. |title=Biogeography, Fourth Edition |publisher=Sinauer Associates |isbn=978-0-87893-494-2 |page=426|year=2010 }}</ref><ref name=West-Eberhard>{{cite book |last=West-Eberhard |first=Mary Jane |author-link=Mary Jane West-Eberhard |title=Developmental Plasticity and Evolution |pages=353–376 |year=2003 |publisher=Oxford University Press |isbn=978-0-19-512235-0}}</ref><ref>{{cite book |last1=Sanderson |first1=Michael J. |last2=Hufford |first2=Larry |title=Homoplasy: The Recurrence of Similarity in Evolution |url=https://books.google.com/books?id=WWGNzeNmRUYC&pg=PA330 |year=1996 |publisher=Academic Press |isbn=978-0-08-053411-4 |pages=330, and passim |access-date=2017-01-21 |archive-url=https://web.archive.org/web/20170214233633/https://books.google.com/books?id=WWGNzeNmRUYC&pg=PA330 |archive-date=2017-02-14 |url-status=live }}</ref>

===Atavism===

{{Main|Atavism}}

In some cases, it is difficult to tell whether a trait has been lost and then re-evolved convergently, or whether a gene has simply been switched off and then re-enabled later. Such a re-emerged trait is called an [[atavism]]. From a mathematical standpoint, an unused gene ([[genetic drift|selectively neutral]]) has a steadily decreasing [[probability]] of retaining potential functionality over time. The time scale of this process varies greatly in different phylogenies; in mammals and birds, there is a reasonable probability of remaining in the genome in a potentially functional state for around 6 million years.<ref>{{Cite journal |last1=Collin |first1=R. |last2=Cipriani |first2=R. |year=2003 |title=Dollo's law and the re-evolution of shell coiling |journal=Proceedings of the Royal Society B |volume=270 |issue=1533 |pages=2551–2555 |doi=10.1098/rspb.2003.2517 |pmc=1691546 |pmid=14728776}}</ref>

===Parallel vs. convergent evolution===

[[File:Evolutionary trends.svg|thumb|upright=1.5|Evolution at an [[amino acid]] position. In each case, the left-hand species changes from having alanine (A) at a specific position in a protein in a hypothetical ancestor, and now has serine (S) there. The right-hand species may undergo [[divergent evolution|divergent]], parallel, or convergent evolution at this amino acid position relative to the first species.]]

When two species are similar in a particular character, evolution is defined as parallel if the ancestors were also similar, and convergent if they were not.{{efn|However, all organisms share a common ancestor more or less recently, so the question of how far back to look in evolutionary time and how similar the ancestors need to be for one to consider parallel evolution to have taken place is not entirely resolved within evolutionary biology.}} Some scientists have argued that there is a continuum between parallel and convergent evolution,<ref>{{cite journal |last=Arendt |first=J. |author2=Reznick, D. |title=Convergence and parallelism reconsidered: what have we learned about the genetics of adaptation?|journal=Trends in Ecology & Evolution|date=January 2008 |volume=23 |issue=1 |pages=26–32 |doi=10.1016/j.tree.2007.09.011 |pmid=18022278 |bibcode=2008TEcoE..23...26A }}</ref><ref>{{cite journal |last1=Waters |first1=Jonathan M. |last2=McCulloch |first2=Graham A. |title=Reinventing the wheel? Reassessing the roles of gene flow, sorting and convergence in repeated evolution |journal=Molecular Ecology |date=2021 |volume=30 |issue=17 |pages=4162–4172 |doi=10.1111/mec.16018 |pmid=34133810 |bibcode=2021MolEc..30.4162W |s2cid=235460165 | issn=1365-294X}}</ref><ref>{{cite journal |last1=Cerca |first1=José |title=Understanding natural selection and similarity: Convergent, parallel and repeated evolution |journal=Molecular Ecology |date=October 2023 |volume=32 |issue=20 |pages=5451–5462 |doi=10.1111/mec.17132|pmid=37724599 |bibcode=2023MolEc..32.5451C }}</ref><ref>{{cite journal |last1=Bohutínská |first1=Magdalena |last2=Peichel |first2=Catherine L. |title=Divergence time shapes gene reuse during repeated adaptation |journal=Trends in Ecology & Evolution |date=April 2024 |volume=39 |issue=4 |pages=396–407 |doi=10.1016/j.tree.2023.11.007|pmid=38155043 |bibcode=2024TEcoE..39..396B }}</ref> while others maintain that despite some overlap, there are still important distinctions between the two.<ref>{{cite journal |last=Pearce |first=T. |title=Convergence and Parallelism in Evolution: A Neo-Gouldian Account |journal=The British Journal for the Philosophy of Science |date=10 November 2011 |volume=63 |issue=2 |pages=429–448 |doi=10.1093/bjps/axr046|doi-access=free}}</ref><ref name="Zhang">{{cite journal | last1=Zhang | first1=J. |last2=Kumar |first2=S. |year=1997 | title=Detection of convergent and parallel evolution at the amino acid sequence level | journal=Mol. Biol. Evol. |volume=14 |issue=5| pages=527–36 |doi=10.1093/oxfordjournals.molbev.a025789 |pmid=9159930 |doi-access=free}}</ref>

When the ancestral forms are unspecified or unknown, or the range of traits considered is not clearly specified, the distinction between parallel and convergent evolution becomes more subjective.  For instance, the striking example of similar placental and marsupial forms is described by [[Richard Dawkins]] in ''[[The Blind Watchmaker]]'' as a case of convergent evolution, because mammals on each continent had a long evolutionary history prior to the extinction of the dinosaurs under which to accumulate relevant differences.<ref>{{cite book|last=Dawkins|first=Richard|author-link=Richard Dawkins|year=1986|title=The Blind Watchmaker|publisher=W. W. Norton|isbn=978-0-393-31570-7|pages=[https://archive.org/details/blindwatchmaker00rich/page/100 100–106]|title-link=The Blind Watchmaker}}</ref>