Editing Snake (section)

=== Genetic basis of snake evolution ===
{{Main|Limb development}}
Both fossils and [[Phylogenetics|phylogenetic]] studies demonstrate that snakes evolved from [[lizard]]s, hence the question became which genetic changes led to limb loss in the snake ancestor. Limb loss is actually very common in extant reptiles and has happened dozens of times within [[skink]]s, [[Anguidae|anguids]], and other lizards.<ref>{{cite journal |last1=Bergmann |first1=Philip J. |last2=Morinaga |first2=Gen |title=The convergent evolution of snake-like forms by divergent evolutionary pathways in squamate reptiles |journal=Evolution |date=March 2019 |volume=73 |issue=3 |pages=481–496 |doi=10.1111/evo.13651 |pmid=30460998 }}</ref>

In 2016, two studies reported that limb loss in snakes is associated with DNA mutations in the Zone of Polarizing Activity Regulatory Sequence (ZRS), a regulatory region of the [[sonic hedgehog]] gene which is critically required for limb development. More advanced snakes have no remnants of limbs, but basal snakes such as pythons and boas do have traces of highly reduced, vestigial hind limbs. Python embryos even have fully developed hind limb buds, but their later development is stopped by the DNA mutations in the ZRS.<ref>{{Cite news |url=https://www.theatlantic.com/science/archive/2016/10/what-a-legless-mouse-tells-us-about-snake-evolution/504779/ |title=What a Legless Mouse Tells Us About Snake Evolution |newspaper=[[The Atlantic]] |access-date=October 25, 2016 |url-status=live |archive-url=https://web.archive.org/web/20161024222452/http://www.theatlantic.com/science/archive/2016/10/what-a-legless-mouse-tells-us-about-snake-evolution/504779/ |archive-date=October 24, 2016}}</ref><ref>{{Cite news |url=http://www.livescience.com/56573-mutation-caused-snakes-to-lose-legs.html |title=Snakes Used to Have Legs and Arms … Until These Mutations Happened |newspaper=Live Science |access-date=October 22, 2016 |url-status=live |archive-url=https://web.archive.org/web/20161022150634/http://www.livescience.com/56573-mutation-caused-snakes-to-lose-legs.html |archive-date=October 22, 2016}}</ref><ref>{{cite journal |vauthors=Leal F, Cohn MJ |title=Loss and Re-emergence of Legs in Snakes by Modular Evolution of Sonic hedgehog and HOXD Enhancers |journal=[[Current Biology]] |volume=26 |issue=21 |pages=2966–2973 |date=November 2016 |pmid=27773569 |doi=10.1016/j.cub.2016.09.020 |doi-access=free|bibcode=2016CBio...26.2966L }}</ref><ref>{{cite journal |vauthors=Kvon EZ, Kamneva OK, Melo US, Barozzi I, Osterwalder M, Mannion BJ, Tissières V, Pickle CS, Plajzer-Frick I, Lee EA, Kato M, Garvin TH, Akiyama JA, Afzal V, Lopez-Rios J, Rubin EM, Dickel DE, Pennacchio LA, Visel A |display-authors=6 |title=Progressive Loss of Function in a Limb Enhancer during Snake Evolution |journal=[[Cell (journal)|Cell]] |volume=167 |issue=3 |pages=633–642.e11 |date=October 2016 |pmid=27768887 |pmc=5484524 |doi=10.1016/j.cell.2016.09.028 |url=}}</ref>