Editing Chicken or the egg (section)

==Scientific resolutions==
Although the question is typically used metaphorically, [[evolutionary biology]] provides literal answers, made possible by the Darwinian principle that species [[Evolution|evolve]] over time, and thus that chickens had ancestors that were not chickens,<ref name="Fabry" /> similar to a view expressed by the Greek philosopher [[Anaximander]] when addressing the paradox.<ref name="paradox" /> 

If the question refers to eggs in general, the egg came first. The first [[amniote]] egg – that is, a hard-shelled egg that could be laid on land, rather than remaining in water like the eggs of fish or amphibians – appeared around 312 million years ago.<ref>{{Cite journal|last1=Benton|first1=Michael J.|last2=Donoghue|first2=Philip C. J.|date=2007-01-01|title=Paleontological Evidence to Date the Tree of Life|url=https://academic.oup.com/mbe/article/24/1/26/1070944|journal=[[Molecular Biology and Evolution]]|volume=24|issue=1|pages=26–53|doi=10.1093/molbev/msl150|issn=0737-4038|pmid=17047029|doi-access=free}}</ref> In contrast, chickens are domesticated descendants of [[red junglefowl]] and probably arose little more than eight thousand years ago, at most.<ref>{{Cite journal|last1=Miao|first1=Y-W|last2=Peng|first2=M-S|last3=Wu|first3=G-S|last4=Ouyang|first4=Y-N|last5=Yang|first5=Z-Y|last6=Yu|first6=N|last7=Liang|first7=J-P|last8=Pianchou|first8=G|last9=Beja-Pereira|first9=A|date=2012-12-05|title=Chicken domestication: an updated perspective based on mitochondrial genomes|journal=[[Heredity (journal)|Heredity]]|language=en|volume=110|issue=3|pages=277–282|doi=10.1038/hdy.2012.83|issn=1365-2540|pmc=3668654|pmid=23211792}}</ref>

If the question refers to ''chicken'' eggs specifically, the answer is still the egg, but the explanation is more complicated.<ref name=SOR>{{cite journal|first= Roy A. |last=Sorensen|title=The Egg came before the chicken|journal=Mind|volume=101|number=403|pages=541–542|year=1992|url=https://academic.oup.com/mind/article-abstract/101/403/541/947797?redirectedFrom=fulltext|doi=10.1093/mind/101.403.541}}</ref> The process by which the chicken arose through the interbreeding and domestication of multiple species of wild jungle fowl is poorly understood, and the point at which this evolving organism became a chicken is a somewhat arbitrary distinction. Whatever criteria one chooses, an animal nearly identical to the modern chicken (i.e., a [[wiktionary:proto-|proto]]-chicken) laid a fertilized egg that had DNA making it a modern chicken due to mutations in the mother's ovum, the father's sperm, or the fertilised [[zygote]].<ref>{{cite web
| title=Finally answered! Which came first, the chicken or the egg?
| url=https://www.mnn.com/earth-matters/animals/stories/finally-answered-which-came-first-the-chicken-or-the-egg
| first=Melissa
| last=Breyer
| date=2013-02-11
| website=[[Mother Nature Network]]
| access-date=2017-07-11}}</ref><ref name="Fabry" /><ref name="Zushi">{{cite news|last=Zushi |first=Yo |publisher=NewStatesman.com |date=27 February 2017|title=Which came first: the chicken or the egg? |url=https://www.newstatesman.com/2017/which-came-first-chicken-or-egg}}</ref><ref name="NBCnews.com">{{cite news|publisher=NBCnews.com |date=14 July 2010|title=Which came first, the chicken or the egg? British scientists claim to have solved the mystery|url=https://www.nbcnews.com/id/wbna38238685}}</ref>

It has been suggested that the actions of a [[protein]] found in modern chicken eggs may make the answer different.<ref name="Zushi" /><ref name="NBCnews.com"/> In the uterus, chickens produce ovocleidin-17 (OC-17), which causes the formation of the thickened [[calcium carbonate]] shell around their eggs. Because OC-17 is expressed by the hen and not the egg, the bird in which the protein first arose, though having hatched from a non-reinforced egg, would then have laid the first egg having such a reinforced shell: the chicken would have preceded this first 'modern' chicken egg.<ref name="Zushi" /><ref name="NBCnews.com"/> However, the presence of OC-17 or a homolog in other species, such as turkeys<ref>{{cite journal|last1=Mann|first1=Karlheinz|last2=Mann|first2=Matthias|title=The proteome of the calcified layer organic matrix of turkey (Meleagris gallopavo) eggshell|journal=Proteome Sci.|year=2013|volume=11|issue=1|page=40|doi=10.1186/1477-5956-11-40|pmid=23981693|pmc=3766105 |doi-access=free }}</ref> and finches<ref>{{cite journal|last=Mann|first=Karlheinz|title=The calcified eggshell matrix proteome of a songbird, the zebra finch (Taeniopygia guttata)|journal=Proteome Sci.|year=2015|volume=13|page=29|doi=10.1186/s12953-015-0086-1|pmc=4666066|pmid=26628892 |doi-access=free }}</ref> suggests that such eggshell-reinforcing proteins are common to all birds,<ref>{{cite journal|last1=Hincke|first1=Maxwell T.|last2=Nys|first2=Yves|last3=Gautron|first3=Joel|title=The Role of Matrix Proteins in Eggshell Formation|journal=The Journal of Poultry Science|year=2010|volume=47|issue=3|pages=208–219|doi=10.2141/jpsa.009122|doi-access=free}}</ref> and thus long predate the first chickens.