> it’s a legitimate question, but the way Taleb is using it as some kind of gotcha! query suggests that he isn’t really asking it in good faith.

Or, more generously (as to Taleb’s character) that the implicit premise (if there were ethnic diversity, we would have robust genetic evidence) justifying his argument is itself not based on a well-informed understanding of the context.

This time period is separated by centuries of plague, smallpox, and high infant mortality. I would not be surprised that genetic diversity would simply vanish over time.

She said "very little" Norman genes, not none at all. Given that the normal story of the Norman invasion is not about mass invasion, but the replacement of one ruling class with another, so relatively few actual people, this would not seem to be surprising.

I doubt you could even define "Norman genes" properly. How would they be different to say "Danish genes", wich migrated to Britain between the 8th and 10th century. After all Normans were also just Scandinavian people who relocated to northern France in the 10th century. The Normans integrated quickly into french (frankish) society by adaptding the language and intermarriage. Furthermore "Norman genes" should also be found in southern Italy, since it was the Normans who founded the Kingdom of Sicily, before it was incoorperated into the Holy Roman Empire.

> the same study failed to find Norman genes either

How would a Norman gene be different from a French or Norse one?

This could be seen as framing it as being a Roman Occupation of Britain.

There is genetic evidence of people from the Balkans migrating to Wales during the Roman era: https://academic.oup.com/mbe/article-lookup/doi/10.1093/molb...

That's not true. East Anglia, the region with the most Germanic ancestry, is only ~30%.