Editing Atavism (section)

{{Short description|Reappearance of a genetic trait once thought extinct}}
{{other uses}}
{{Original research|date=May 2023}}
[[File:Tubal Pregnancy with embryo.jpg|thumb|Early [[embryo]]s of various species display some ancestral features, like the tail on this human embryo. These features normally disappear in later development, but it may not happen if the animal has an atavism.<ref>{{cite journal|last1=Uthman|first1=Ed|title=Tubal pregnancy with embryo|journal=WikiJournal of Medicine|date=2014|volume=1|issue=2|doi=10.15347/wjm/2014.007|doi-access=free}}
</ref><ref name="universe-review.ca">{{cite web|url=http://universe-review.ca/F10-multicell.htm |title=Multi-cell Organisms |publisher=Universe-review.ca |access-date=2011-09-29}}</ref>]]

In [[biology]], an '''atavism''' is a modification of a biological [[traits]] structure or [[behavior]]<ref>https://pubmed.ncbi.nlm.nih.gov/8693850/</ref> whereby an ancestral genetic [[Trait (biological)|trait]] reappears after having been lost through [[evolution]]ary change in previous generations.<ref name="Briankhall1">{{Citation | title=Developmental mechanisms underlying the atavisms| author=Brian K. Hall| journal=Biological Reviews| year=1984| volume=59| issue=1| pages=89–124| doi=10.1111/j.1469-185x.1984.tb00402.x| pmid=6367843| s2cid=29258934}}</ref> Atavisms can occur in several ways,<ref name=nt>{{cite journal| last1=Tomic|first1=Nenad| last2= Meyer-Rochow|first2= Victor Benno| year= 2011|title= Atavisms - medical, genetic, and evolutionary implications|journal= Perspectives in Biology and Medicine|volume=54 | issue = 3 | pages= 332–353| doi=10.1353/pbm.2011.0034| pmid= 21857125|s2cid=40851098}}</ref> one of which is when [[gene]]s for previously existing [[phenotype|phenotypic]] features are preserved in [[DNA]], and these become expressed through a [[mutation]] that either knocks out the dominant genes for the new traits or makes the old traits dominate the new one.<ref name="Briankhall1"/> A number of traits can vary as a result of shortening of the [[prenatal development|fetal development]] of a trait ([[neoteny]]) or by prolongation of the same. In such a case, a shift in the time a trait is allowed to develop before it is fixed can bring forth an ancestral phenotype.<ref>{{cite book| author=Held, L.| year=2009 | title= Quirks of Human Anatomy, an Evo-Devo Look at the Human Body | publisher= [[Cambridge University Press]] | isbn=978-0-521-73233-8}}</ref> Atavisms are often seen as [[evidence of common descent|evidence of evolution]].<ref name="Briankhall2"/>

In [[social science]]s, atavism is the tendency of reversion: for example, people in the modern era reverting to the ways of thinking and acting of a former time.

The word ''atavism'' is derived from the [[Latin]] ''atavus''—a great-great-great-grandfather or, more generally, an ancestor.