Sources concerning migration
Scotland and Scythia
Craig White.
Medieval texts demonstrate that a Scythian ancestry tradition existed among the Gaels and Scots; they do not, by themselves, prove that the historical Gaels migrated from Scythia. Modern archaeology provides evidence of cultural parallels between certain Celtic peoples and those of the Eurasian steppe.
The Celtic and Eurasian Steppe Connection
One of the most useful modern sources is Jeannine Davis-Kimball's Warrior Women. Note that she does not claim to have proved that the Gaels originated in Scythia, nor does she equate Scythians with Gaels. Instead, she examines cultural, artistic and mythological parallels between the Celtic world and the Eurasian steppe (Chapters 11-13).
In Chapter 11 ("Irish Warrior Queens and the Damsels of Death," pp. 186-210), she compares Celtic artistic representations of animals with the Animal Style of Eurasian nomads and discusses possible connections with the ancient Xinjiang "mummy people" (p. 187) referred to in the Appendix. Who are the Red-Haired Peoples of Russia? On p. 190 she compares Irish/Celtic practices with those associated with the Scythians, including treatment of heads and skulls. Chapter 12 ("From Celts to Mongols," pp. 211-216) includes Wales, England and Scotland in discussions of Celtic warrior goddesses. Chapter 13 (pp. 234-239) references motifs associated with the Saka and Sauromatians (Sarmatians) that also occur in Celtic art and mythology. The significance of her argument is that it identifies similarities in artistic and mythological motifs in addition to the presence of warrior women.
Edmund Spenser's A View of the Present State of Ireland (c. 1596) is a dialogue between Eudoxus and Irenius. It was not published in Spenser's lifetime and first appeared in print in 1633 (edited by James Ware). He quote Irenus as stating of the Irish that "I suppose to bee Scythians ... for those Scots are Scythians, arrived (as I said) in the North parts of Ireland" (pp. 58, 60) This version published 1809, Dublin Reprinted at the Hibernia Press. In a footnote on page 64 he states:
"Bede tells us that the Picts were a colony of Scythians, who first comming into Ireland, and being denyed residence there by the Scots, were persuaded by them to inhabit the North parts of Britaine."
A word search uncovers the Scots-Scythian connection which is made several times throughout the book.
The Medieval Tradition
The ninth-century Historia Brittonum (c. 829-830 AD traditionally associated with Nennius) contains an early migration story involving a nobleman from Scythia who travelled to Egypt around the time of Moses and the Exodus. His people subsequently travelled through North Africa and Iberia before reaching Ireland and ultimately Dal Riata. This predates the fully developed story of Scota, Pharaoh's daughter.
The tradition becomes much more explicit in the Lebor Gabala Erenn (Book of the Taking of Ireland). One particularly important passage identifies the Gaedil as being "of the people of Scythia," because they were descended from Fenius Farsaid, who had the princedom of Scythia (Macalister, Vol. I, p. 153). This means that a medieval Gaelic tradition is associated the ancestors of the Gaels with Scythia. Scota does not appear in the earliest surviving form of the Historia Brittonum story; her literary appearance belongs to later medieval traditions, but seems to have been added a little later due to surviving traditions based on ancient knowledge.
The Declaration of Arbroath (1320)
As discussed earlier, in 1320, Scottish nobles wrote to Pope John XXII stating that the Scots had travelled from Greater Scythia, passing by way of the Mediterranean and the Pillars of Hercules before reaching Spain and eventually Scotland. The route is: Greater Scythia Mediterranean Pillars of Hercules Spain Scotland. This is not a modern interpretation: the political leadership of Scotland in 1320 was itself presenting the Scots as a people who had come from Greater Scythia. The Declaration therefore demonstrates that the Scythian-origin tradition was established in Scottish political thought by the early fourteenth century, and it predates John of Fordun.
Fordun and Bower
John of Fordun's Chronica Gentis Scotorum (1871-72, Book I, Chapters I, V, VIII, IX; pp. 1, 4, 6-7) places Upper Scythia at one geographical extreme and Egypt at the other, and introduces Gaythelos and Scota. Thus Fordun preserves the combined Scythian with Egyptian: Gaythelos + Scota Scottish tradition. Walter Bower's fifteenth-century Scotichronicon (a Latin chronicle of Scottish history) develops the story further, making Gaythelos the husband of Scota, daughter of Pharaoh Chencres, and incorporating it into the national genealogy of the Scots.
The Medieval traditiion does not establish that modern historical research has proved that the Gaels literally migrated from Iron Age Scythia. Medieval writers did not possess modern archaeology, historical linguistics or population genetics. The texts should first be understood as evidence of what medieval Irish and Scottish writers believed about their origins.
What Modern Genetics Adds
A major genetic study is Maja Krzewi ska et al., "Ancient genomes suggest the eastern Pontic-Caspian steppe as the source of western Iron Age nomads," Science Advances, Vol. 4, No. 10, eaat4457 (2018). The researchers examined 35 ancient genomes associated with Srubnaya-Alakulskaya, Cimmerian, Scythian and Sarmatian populations. The study found genetic relationships among these ancient populations, but its conclusions were cautious. It did not prove that modern Ossetians are direct descendants of the sampled Scythians or Sarmatians; that the Srubnaya people were direct ancestors of the Slavs; or that modern ethnic groups can be traced directly to one particular ancient population.
The "R1a/R1b" argument
This DNA argument needs caution. The article also discusses Y-chromosome haplogroups and makes an argument along the lines of:
Srubnaya predominantly R1a
modern Russians/Ukrainians/Belarusians/Poles substantial R1a
Cimmerians/Scythians/Sarmatians more R1b
therefore Slavs may descend from populations related to Srubnaya.
This is too simplistic genetically.
A Y-chromosome haplogroup is only one paternal lineage. It does not represent someone's entire ancestry.
For example, saying:
"Population A has lots of R1a and population B has lots of R1a"
doesn't establish that:
"Population A is the ancestor of population B."
Nor does:
"Population A has R1b and population B has R1b"
establish direct descent.
This is why I am so cautious using Y-DNA data and assembled the paper "The Bible and Genetics" -Y-DNA is a tracer, not a race. One can have a trace of another bloodline in one's racial or ethnic composition. The paper by Maja Krzewska et al itself uses multiple genetic analyses rather than treating a single Y-haplogroup as an ethnic identity. Its overall conclusion is specifically that the populations cannot simply be assigned direct ancestor/descendant relationships.
Conclusion
Irish sources preserve a tradition connecting the ancestors of the Gaels with Scythia. The Declaration of Arbroath of 1320 provides evidence that medieval Scottish political leaders themselves claimed that their people came from Greater Scythia. Fordun and Bower developed the Scythian, Egyptian, Gaythelos and Scota traditions from ancient sources. Davis-Kimball identifies parallels between Eurasian steppe cultures and Celtic art, mythology and traditions, including material relating to Scotland. The genetic evidence is more not overwhelming and does not establish a simple direct line from Scythians or Sarmatians to modern ethnic groups. Nor should one expect that given so much complexity is involved and Y-DNA chromosome research is not perfect and is interpretive. After all there are jumping genes, mutations and many discrepancies which are yet to be fathomed and explained. Geneticists ask the question: "how far back in time does DNA match still have genealogical have any meaning?"
What we can conclude is that the Scythian ancestry of the Scots and Gaels is a genuine and well-documented medieval tradition based on ancient sources. Modern archaeology also identifies intriguing cultural parallels between the Celtic world and the Eurasian steppe.
References
Davis-Kimball, J. & Behan, M., 2002, Warrior Women: An Archaeologist's Search for History's Hidden Heroines.
Macalister, R. A. S. (ed. and trans.), 1932-1942 (Vol. 1), Lebor Gabala Erenn: The Book of the Taking of Ireland.
Nennius (c. 829-830), Historia Brittonum.
Scottish baron], 1320, Declaration of Arbroath (letter to Pope John XXII).
Fordun, J. of (ed. Skene, W. F.), 1871-1872, Johannis de Fordun Chronica Gentis Scotorum.
Bower, W. (general ed.) (et. al.), (1987-1998), Scotichronicon.
Krzewi ska, M. (et. al.). (2018), "Ancient genomes suggest the eastern Pontic-Caspian steppe as the source of western Iron Age nomads," Science Advances, Vol. 4, No. 10, eaat4457.
Edmund Spenser, E. (c. 1596). A View of the Present State of Ireland. This version published 1809.