Razib Khan One-stop-shopping for all of my content

August 15, 2017

Roman cultural history has almost no demographic imprint

Filed under: ancient Population Genetics,History,Mary Beard,Roman History — Razib Khan @ 9:48 am

Several friends have asked that I weigh in the recent dust-up between Nassim Nicholas Taleb and Mary Beard. I haven’t for a few reasons. First, I can’t really be bothered to go incognito and see every detail of Taleb’s argument, as he has me blocked on Twitter (he called me a fucking idiot or something at some point). Second, the passion around this topic has little to due with genetics or ancient history from what I can see, two topics which I am actually interested in. Rather, it’s more about contemporary geopolitics. This is interesting too, and I have opinions on that, but I try really hard to keep history and politics in separate silos unless I am explicit about the connections and relevance. That’s because I don’t see classical history as simply something instrumentally important for modern times, but interesting in and of itself (the same goes for population genetics).

And for what it’s worth, Mary Beard says the same in her conclusion to SPQR. The ancients were ancients. Let them be what they were.

That being said, as someone with knowledge sets in ancient history and historical population genetics, I will make a few statements and let others interpret them however they wish (to be frank, I’m not going to cede ground to any of the experts I’ve seen who hae spoken on the intersection of these two knowledge sets, so I figured it was time to put something somewhere beside Twitter).

* The prior probability that a Roman officer of the period in Britain would have visible black African ancestry (as seems clear by the cartoon, though no one has asked the cartoonists what their intent was) probability seems rather low. But it is non-zero, because a small minority of Roman subjects and citizens would have been defined as black by their physical appearance if they were alive today (they are mentioned passingly in the literature and texts from the period). Including in Britain.

* The probability conditional that he was based on an officer in Britain who was a native of Tidis is low, but higher. Several historians have pointed out in defense of the cartoon’s plausibility that there were many North Africans in Roman service, as well as prominent North Africans in Roman history (to name three of note, Septimius Severus, Tertullian, and St. Augustine). Whole tribes of what we’d today term Berbers enrolled in the Roman military a federates.

There are several separate issues to note. First, of the many North African genotypes I’ve seen detectable Sub-Saharan ancestry is found in almost all of them. But, many (most?) North Africans do not look visibly of Sub-Saharan African ancestry (see list of heads of states of Algeria). Second, both historical and genetic evidence indicates that this admixture from Sub-Saharan Africa is overwhelmingly (though not exclusively) from the period after Islam and the rise of a much bigger trans-Saharan trade (see Genomic Ancestry of North Africans Supports Back-to-Africa Migrations). Modern North Africa does have a large population today of people who are black or of obvious part-black ancestry, but this is due to the slave trade under Islam, and not antiquity.

* As evidence of the lack of non-European ancestry the paper The fine-scale genetic structure of the British population has been submitted. This is a great paper with best-of-breed methods and a massive data set of native English, with regional data. How do we resolve textual and archaeological evidence of people born outside of Britain during the Roman period in Britain with their lack of long-term genetic footprint among native modern Britains?

These sorts of questions need to be integrated in a broader context of the demography and genetics of antiquity that we have. On the whole looking at papers on modern and ancient DNA I am surprised by the lack of perturbation on the genetic structure attributable to the Roman period across Western Eurasia. I will offer two likely reasons that are related.

First, Classical civilization was an urban one, and the textual evidence we have is going to be highly skewed culturally in terms of our perception. The Roman world was predominantly written in cultured Latin and Greek (from what I have read the early translations of the Bible are indicative of a more pedestrian background of Christians due to the class markers of their lexical choices and idioms). But it was not necessarily spoken in cultured Latin and Greek across vast swaths of its territory. Even in St. Augustine’s time Punic was still spoken the North Africa countryside, while the persistence and resurgence of Basque and Berber, and perhaps Brythonic Celtic in Britain, attest to vast reservoirs of people who were under the Roman peace, but not of it (also, the persistence of Albanian from a native Illyrian substrate). Because of the resources historians have on hand, text, there is going to be a major lacunae in our understanding and perception of the past. We hear the urban elites speaking to us. Not the rural majority.

Second, Classical civilization was an urban one, and this might have a major impact on the demographic consequences of migration. At any given size the effective breeding population is smaller than the census population, and the breeding population may not be representative of the overall population in terms of their genetic character. More specifically, it seems highly possible that the cosmopolitan urban Roman cities were massive demographic sinks. Rome before the Gothic Wars wars was a massive city, not too far on the path of decline from its early imperial peak. But by the year 600 it had decreased its population to the point that vast swaths of the city were abandoned. Where did these people go? No doubt some of the elites scattered. Cassiodorus simply moved when barbarism came to his front step. But this was less possible for the urban proletariat. There is strong evidence that slaves in the ancient world were not replacing themselves reproductively due to brutality under which they lived. Some of the same was likely true of the urban proletariat.

* There is a difference between the inheritance pattern of culture and genes. In The Geography of Recent Genetic Ancestry across Europe this passage has always stuck out for me: “There is relatively little common ancestry shared between the Italian peninsula and other locations, and what there is seems to derive mostly from longer ago than 2,500 ya…The rate of genetic common ancestry between pairs of Italian individuals seems to have been fairly constant for the past 2,500 years, which combined with significant structure within Italy suggests a constant exchange of migrants between coherent subpopulations.”

The straightforward conclusion from this is that the Latinization of the Italian tribes and Magna Graecia occurred with no great demographic transformation. Modern Italy has within it the ghost of tribes long gone. This is notable because if you read the historical records of the Roman period you see evidence of trade, transport, and migration. But the genetic data would not lead you to this conclusion outside of Sicily and a few parts of Southern Italy.*

Above I have presented my reasoning for why this might be. But I think what it tells us that genetic data can informs us when there is a demographic turnover, and therefore a cultural turnover, but it will miss cultural turnovers which don’t have demographic impacts. These are many. To give a few examples, the rise of Islam in South Asia and Southeast Asia, the Latinization of the Western Mediterranean, the de-Latinization of Britain after the withdrawal of Roman legion and before the mass arrival of Saxons, and arrival of Buddhism in East Asia. All these are massive historical and cultural events, but they would not be visible in the genetic record.

If you want to learn about Roman history there are many books you could read. But I do recommend you try Bryan Ward-Perkins’ The Fall of Rome: And the End of Civilization. It’s a nice materialist take, and I think it gets to the underlying dynamics of institutional fragility of ancient civilization which was so easily wiped away by barbarism.

Addendum: The migration of the Slavs, Anglo-Saxons, and the Islamic Empires, all seem to differ from antiquity in having a major demographic impact. Why? I the case of massive institutional collapse, as in the first two cases, very old dynamics of inter-group competition arise, and famine probably does the rest of the trick. For Islam, it was a genuinely cosmopolitan civilization, with a more complex gradation between free and slave than in antiquity. Though it was quite brutal, African and Turkish slaves became free, and their genetic impact can be seen throughout the Islamic world.

* Like Spain, a substantial proportion of the Sicilian gene flow exchanged is almost certainly due to the Islamic period. There are segments of North African and Sub-Saharan ancestry in Sicilians, albeit to a smaller extent than in Spain (in keeping with the shorter time period as part of the Islamic world).

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