I am often struck by how we are the results of random choices by our ancestors, decisions to move, to immigrate, to live one place rather than another. My parents might never have met if my grandfather had not lost his business during the 1920's and moved from one side of Vermont to another. My father would not have been living there if his parents had not decided to finally settle permanently in Vermont. His family had a history of almost 100 years of going back and forth to Canada. He was born in Canada. Recently I had my DNA tested for ethnic origin, thinking it might answer some questions. Like many genealogical answers it only provided more questions.
My limited understanding of how DNA works is that you get pieces from both parents: 1/2 from each. What pieces they pass along may differ. My profile is came out as 58% British Isles, 19% Scandinavian, 17% Southern European and 6% other. However my sibling's is 78% Scandinavian, 19% Southern European and 3% other. With an Irish mother it does seem strange that there is no British Isles DNA in her profile. Looking at the migration patterns of the Celts below it is also possible that they may have contributed to the Southern European DNA that both of us have. Viking DNA is distributed widely over Europe: Ireland and France would both have Scandinavian DNA. Irish legendary migration histories have the invaders coming to the island through what is now the Iberian peninsula.
The migration of the Celtic tribes across Europe reached the Irish isle in the period from 2000-300 B.C. These peoples probably carried DNA from what is now Austria, France, and Spain. Ireland is unique in that it was never invaded or conquered by the Romans who occupied what is today modern Britain and Scotland.
I was expecting my Irish mother to contribute British Isles and Scandinavian DNA. The Vikings founded the cities of Ireland when they were tired of plundering and realized they could make a bigger profit by becoming merchant traders. These "trading posts" developed into the cities of Dublin, Waterford, Limerick, Cork and others. I suspected there was some Welsh ancestry and one line is Norman Irish which could either bring the Scandinavian or British Isles genes.
From my Dad obviously I got some British Isles, Scandinavian and Southern European - he was French Canadian and part Native American which might account for the 6% other. I wondered why it did not reflect central European DNA - which covers France. So I started to look at the history. Given the immigration statistics on the areas where his ancestors originated I found the Celts and Vikings again. Normandy and the area around Paris were Celtic strongholds. Paris, a Roman city was taken over by Frankish tribal peoples and attacked by the Vikings. There were many immigrants from La Rochelle and surrounding areas passed back and forth in the middle ages between English and French control. More British DNA perhaps? That area was also settled by the Romans - more southern European DNA? What I didn't expect was the Visigoths.
The Visigoths were a "barbarian" people who had invaded Italy and Rome in the late 4th and early 5th century. They migrated through the Mediterranean countries and became sufficiently powerful to fight a successful war with the Romans whom they defeated in 378. A treaty allowed them to fight on the side of Rome until conflict broke out and they sacked Rome in 410. They swept into the power vacuum left by the declining Roman empire in the 5th century. They converted to Christianity and became the civil authority in the structures of the empire left behind. Their capital was at Toulouse. (We have a double connection with Toulouse through my great grandmothers Adelaide and Virginia Raymond dite Toulouse) The settlements in France were largely in the south west along the Garonne River. The Visigoth kingdom in Gaul was defeated by Clovis in 507. The main territory remained Spain and Portugal, at least until the 8th century when there was a Muslim invasion. They may account for the southern European DNA.
DNA opens interesting windows into the past. Its bits and pieces have been sorted and passed on from parents to children for centuries.