January 23, 2009

Genetics & History

A quick response to Matthew Roberts’ response on genetics:

What genetics does not suggest this?  The only way one could conduct a conclusive study would be to take a large sample of DNA from the remains of republican Romans and compare it to the DNA from imperial remains (a difficult task because of cremation).

Ancient DNA extraction is getting much better. Cremation is a real issue, but not everyone would get cremated (e.g., the Cornelii practiced inhumation from what I recall), and DNA has been extracted even from cremated remains. But we don’t need to wait on ancient DNA extraction, surveys of the patterns of genetic variation in modern populations are used to make inferences about the past.  These may never be conclusive, but then history rarely is in any case.  If any are curious on my ScienceBlog I have several posts on genetic maps of Europe. Today I posted on the origins of Ashkenazi Jews.  Inferences from patterns of genetic variation can tell us whether the Greek settlement of Magna Graecia left an impact (likely), or whether the Anglo-Saxons had a genetic impact on the British Isles (some, but a sharp drop off from East Anglia), or whether Muslims and Christians in Lebanon differ in their ancestry (some, perhaps due to the intermarriage between Muslim converts and Arabians after the Islamic conquest).  The size of the barbarian hordes is under some dispute by traditional historians (see The Ruin of the Roman Empire by James J. O’Donnell for a low-ball figure), but surveying the pattern of genetic variation in Europe today suggests that the genetic impact of northern barbarians or non-Italians in Italy was not substantial from what I can see (aside from Magna Graecia, where the Greeks were operationally natives by the time of the Roman Republic).*  We not only have a qualitative sense, but a quantitative sense of particular contributions of ancestry from and to various regions (e.g., North African male legacy in southern Europe quantified).  As for the polyglot nature of urban Rome, it seems entirely likely to me.  But I don’t think this had much of a genetic impact because up until the year 1900 the world’s cities were massive genetic blackholes.  Cities only kept their population up through migration, which explains how Rome shrunk to 30,000 inhabitants by the 7th century.

For readers who are more interested, please see my posts on European genetic substructure.  And again, I think Matthew makes generally correct points. But I disagree with some of the illustrations used, and particular points of detail.  Perhaps my main point would be a stance of exceeding care when using Roman analogies because of the large structural differences between then and now (Rome was a city-based civilization, so the change in the ethnic character of Rome might be very significant, without that change entailing any long term replacement of native stock, as seems to be the case).

* See the work on Etruscans for the kind of thing that would jump out when a large number of foreigners move long distances to settle new lands.

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