Editing Common raven (section)

=== Evolutionary history ===
The common raven evolved in the [[Old World]] and crossed the [[Bering land bridge]] into North America.<ref>[[#Marzluff|Marzluff and Angell]], p. 86</ref> Recent genetic studies, which examined the [[DNA]] of common ravens from across the world, have determined that the birds fall into at least two [[clade]]s: a [[California]] clade (subspecies ''C. c. clarionensis''), found only in the southwestern United States, and a [[Holarctic]] clade, found across the rest of the Northern Hemisphere. Birds from both clades look alike, but the groups are genetically distinct and began to diverge about two million years ago.<ref name=USGS/><ref name="Omland2000">{{cite journal |author= Omland KE|author2= Tarr CL|author3= Boarman WI|author4= Marzluff JM|author5= Fleischer RC |year=2000 |title=Cryptic genetic variation and paraphyly in ravens |journal=[[Proceedings of the Royal Society B]] |volume=267 |issue= 1461|pages=2475–2482|doi=10.1098/rspb.2000.1308 |pmid= 11197122 |pmc= 1690844}}</ref>

The findings indicate that based on [[mitochondrial DNA]], common ravens from the rest of North America are more closely related to those in Europe and Asia, than to those in the California clade, and that common ravens in the California clade are more closely related to the [[Chihuahuan raven]] (''C. cryptoleucus'') than to those in the Holarctic clade.<ref name=USGS>{{cite web|url=http://www.werc.usgs.gov/news/2000-12-19.html|title=California Ravens Are a Breed Apart|access-date=2007-05-11|author=US Geological Survey|archive-date=2017-07-08|archive-url=https://web.archive.org/web/20170708043602/https://www.werc.usgs.gov/news/2000-12-19.html|url-status=dead}}</ref><ref name="Omland2000"/> Ravens in the Holarctic clade are more closely related to the [[pied crow]] (''C. albus'') than they are to the California clade.<ref name="Feld05">{{cite journal| last=Feldman| first=Christopher R.|author2=Omland, Kevin E. |date=March 2005| title=Phylogenetics of the common raven complex (''Corvus'': Corvidae) and the utility of ND4, COI and intron 7 of the β-fibrinogen gene in avian molecular systematics| journal=Zoologica Scripta|volume=34| issue=2| pages=145–156|doi=10.1111/j.1463-6409.2005.00182.x| s2cid=85196387}}</ref> Thus, the common raven species as traditionally delimited is considered to be [[paraphyletic]].<ref name=Feld05/>

One explanation for these genetic findings is that common ravens settled in California at least two million years ago and became separated from their relatives in Europe and Asia during a [[glacial period]]. One million years ago, a group from the California clade evolved into a new species, the Chihuahuan raven. Other members of the Holarctic clade arrived later in a separate migration from Asia, perhaps at the same time as humans and [[wolf|wolves]] about 15,000 years ago.<ref name=HBW/><ref>[[#Marzluff|Marzluff and Angell]], pp. 86–87</ref>

A 2011 study suggested that there are no restrictions on [[gene flow]] between the Californian and Holarctic common raven groups, and that the lineages can remerge, effectively reversing a potential speciation.<ref name= random>{{cite journal | last1 = Webb | first1 = William C. | last2 = Marzluff | first2 = John M. | last3 = Omland | first3 = Kevin E. | title = Random interbreeding between cryptic lineages of the Common Raven: evidence for speciation in reverse | journal = Molecular Ecology| volume = 20 | issue = 11| pages =2390–2402 | year = 2011 | doi = 10.1111/j.1365-294X.2011.05095.x | pmid = 21518060| bibcode = 2011MolEc..20.2390W | s2cid = 7684306 }}</ref>

A recent study of raven mitochondrial DNA showed that the isolated population from the [[Canary Islands]] is distinct from other populations.<ref name="Bakom06">{{cite journal| last=Baker| first=Jason M.|author2=Omland, Kevin E. |date=January 2006| title=Canary Island Ravens ''Corvus corax tingitanus'' have distinct mtDNA| journal=Ibis|volume=148| issue=1| pages=174–178| doi=10.1111/j.1474-919X.2006.00493.x}}</ref> The study did not include any individuals from the North African population,<ref name="Bakom06"/> and its position is therefore unclear, though its [[Morphology (biology)|morphology]] is very close to the population of the Canaries (to the extent that the two are often considered part of a single subspecies).<ref name=Clements/>