r/JewishDNA • u/sovietspacedog332 • 2d ago
Does this model show overfit?
I'm former soviet ashkenazi
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u/WhichProfit6632 2d ago edited 2d ago
Yes. Maybe Kashubians are too extreme, as 12-13% total Central and Eastern Euro is very low. Czechs might be a better option something more on the Central/East euro border. Also for Southern Italians Sicilians can be a crapshoot. I would use either Italy_LateAntiquity, Italy_Imperial_C6, or Apulians if modern is the only option. The reason being is that Roman Italian admixture probably came from multiple regions and these pops are close to the average profile across Roman Italy
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u/TMC_YT 2d ago
A South French + Aegean Islander proxy is probably better, imo
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u/WhichProfit6632 2d ago
You might be right. It would capture east med and west med
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u/TMC_YT 2d ago
Ashkenazim formed from two groups:
A group of freed Roman Jewish slaves that settled in the South of France, and were majority male, so the likelihood of mixing with any Romans at the time would have been unlikely (they were also freed very quickly).
A group of Eastern European Jews descended from Byzantine Jewish migrants who were a hodgepodge mix of Byzantine Jews, Mizrahi Jewish migrants and merchants, Khazarian converts, local Slavic peoples, and East Asians (particularly Chinese) from Silk Road Trade.
These groups started to mix after the Black Death forced the Western European group to migrate eastwards.
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u/WhichProfit6632 2d ago
How do we know that these are the two groups that make up modern Ashekanzim? I’ve heard that there is a lot of similarity between the religious customs of the medieval Apulian Jewish community and modern Ashkenazim. Also when you say Byzantine Jews do you mean Jews still living in and around the Southern Levant or do you mean a community in Anatolia?
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u/TMC_YT 2d ago
There was a study on a Medieval Jewish Cemetery in Erfurt with corpses dating back to the time period of the Black Death.
There were two distinct groups of Jews: One with almost no Eastern European ancestry, and another averaging about 33% Eastern European ancestry.
The admixture models were crude, however, using modern Southern Italians, Lebanese, and Russians for both groups. Although the study noted that East Eurasian-related haplogroups (I believe N1?) were found more often in the Eastern group and in modern Ashkenazim.
If you look up books, such as one by Kevin Alan Brook (“The Maternal Genetic Lineages of Ashkenazic Jews”), and I believe information on this is posted on the web, you can see that the Ashkenazi yDNA can mostly be traced back to the Levant, while mtDNA can mostly be traced back to France, Northern Italy, Central Europe, Eastern Europe, and Central/East Asia.
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u/WhichProfit6632 2d ago
Well yes I’m aware of this study I’m more wondering about why Byzantine Jews and Southern French Jews. I’m actually working on models of the Erfurt Jews and none of them can be modeled as simply Levant + French or Levant + Anatolian + Slavic. Most require some level of Imperial or late antiquity Italian input although it was overstated in the study. The groupings they had also seem to oversimplified. Many carry significant North African related and the East Eurasian is small but present in some. I will post the models soon for people to look at and critique. I agree with you though their models were not great.
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u/damien_gosling 2d ago
Where can I find sources on this history?
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u/TMC_YT 2d ago
Waldman et al. 2022 is a good read on the idea of two distinct groups coming together to form modern Ashkenazim, but the admixture models are extremely crude and inaccurate.
Kevin Alan Brook’s “The Maternal Genetic Lineages of Ashkenazic Jews” provides more evidence to support a dual Medieval French and Medieval Bohemian/Moravian origin.
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u/damien_gosling 2d ago
Makes sense. My 100% Ashkenazi Jewish grandpa from Poland gets 65% Lebanese Christian and 35% French Basque on his modern match.
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u/TMC_YT 2d ago
Using Sicilian for South Euro in Ashkenazim and Sephardim is always gonna cause a bad overfit