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Cities are where people go to flourish, and then die

Stable population structure in Europe since the Iron Age, despite high mobility:

Ancient DNA research in the past decade has revealed that European population structure changed dramatically in the prehistoric period (14,000-3,000 years before present, YBP), reflecting the widespread introduction of Neolithic farmer and Bronze Age Steppe ancestries. However, little is known about how population structure changed in the historical period onward (3,000 YBP – present). To address this, we collected whole genomes from 204 individuals from Europe and the Mediterranean, many of which are the first historical period genomes from their region (e.g. Armenia, France). We found that most regions show remarkable inter-individual heterogeneity. Around 8% of historical individuals carry ancestry uncommon in the region where they were sampled, some indicating cross-Mediterranean contacts. Despite this high level of mobility, overall population structure across western Eurasia is relatively stable through the historical period up to the present, mirroring the geographic map. We show that, under standard population genetics models with local panmixia, the observed level of dispersal would lead to a collapse of population structure. Persistent population structure thus suggests a lower effective migration rate than indicated by the observed dispersal. We hypothesize that this phenomenon can be explained by extensive transient dispersal arising from drastically improved transportation networks and the Roman Empire’s mobilization of people for trade, labor, and military. This work highlights the utility of ancient DNA in elucidating finer scale human population dynamics in recent history.

This is the most important: ‘According to a longstanding historical hypothesis, the Urban Graveyard Effect, the influx of migrants in city-centers disproportionately contributed to death rate over birth rate; a process which would contribute to observing individuals as “transient” migrants…’

To me, it confirms that the urban demographics of the ancient world were always transient because of low total fertility.

13 thoughts on “Cities are where people go to flourish, and then die

  1. Of course, as also the paper of Antonio et al. about Imperial Rome demonstrated.

  2. Indeed. Urban sink is the rule throughout history.

    ChangAn, the capital city of both Han and Tang dynasties, had numerous foreign settlement from central asia with caucasian features. The graveyard genetics confirm the historical records.

    However, these foreign immigrants communities always vanished on their own without ethnic cleansing, when trading with west interrupted. The city population again replenished by surrounding native Han farmers.

    Somehow Jewish people are able to resist the urban sink effectively. Maybe something to do with their unique faith and habits.

  3. We still have urban sink. Most cities in the West and even in developing world have abysmally low fertility rates. The difference from the past is that rural fertility rate has also collapsed though it is still somewhat higher. People living in cities today won’t have genetic legacy in a few hundred years.

  4. @IC

    Somehow Jewish people are able to resist the urban sink effectively. Maybe something to do with their unique faith and habits.

    But Jews went through significant bottlenecks. A big majority of medieval Jewish lines have not survived to our day. What is impressive is the later population expansion of the Ashkenazi Jews, which started during the late medieval times, that indeed needs an explanation.

  5. @Harry Jecs

    We still have urban sink. Most cities in the West and even in developing world have abysmally low fertility rates. The difference from the past is that rural fertility rate has also collapsed though it is still somewhat higher. People living in cities today won’t have genetic legacy in a few hundred years.

    But the problem is that today there are not high ratios of rural populations in the developed world and even in much of the developing world to replenish the cities and to maintain the birthrate levels, so immigrants from less developed countries and lands can make more lasting demographic impacts today (which is also due to the highly improved transportation and technology and the globalized economy and culture).

  6. The section on Armenia has a weird part in it (I left a comment at biorxiv asking about it but since it was as Guest, probably didn’t go through for whatever reasons), unless I’m really misreading it somehow: “The earlier cluster (C1) includes newly reported samples (n=5) from Beniamin and published ones (n=6) from five other sites. This cluster cannot be modeled by any single source of ancestry using existing data. The later cluster (C2), which contains newly reported samples (n=12) from Beniamin dating between 403 BCE-500 CE, is genetically similar to present-day Armenians (excluding two Kurdish individuals; Figure 2C). Despite the split, there is evidence of partial continuity between the earlier and later clusters: the later (C2) can be modeled using around 50% of the earlier cluster (C1) and an additional source of Steppe ancestry.”

    The earlier cluster C1 includes some of the previously published ARM_MBA-LBA samples judging by the dates given here, while C2 moves towards the contemporary Armenian direction. Then, it’s rather C1 that has greater steppe-rich ancestry and C2 that is more “Mesopotamian”-like and obviously shifted towards that direction in the PCA. Maybe they meant it the other way around i.e. “C1 can be modeled as C2 + steppe-rich source”.

    One of the issues with trying to tell what the steppe-rich source donating to the Armenian MLBA samples was like is that you have a few different options to compare it to “locally” based on published samples that all have unfortunately decent chronological distance, so these might be an interesting addition.

    The two Kurdish samples they mention also have a really weird position in that Figure 2 PCA.

  7. @Onur Dincer:
    Has anyone ever gone the lengths to check for Ashkenazi diffusion into the general population? While there are obvious historical reasons for why many lines and local groups would go extinct in the European Jewish community, I wonder how often it was that people converted or otherwise left the community as a means of evading persecution. There were quite a few famous converted polemicists. Were there ever enough to leave a strong detectable genetic trace?

  8. @Otanes

    Were there ever enough to leave a strong detectable genetic trace?

    Principally on haplogroups as the Jewish autosomal contribution to gentiles would be mostly washed out in several generations. How much Ashkenazi Jews contributed to gentile European haplogroups is an issue waiting to be explored. Not much based on the data I have.

  9. The autosomal signatures of European Jewish admixture would mostly be washed out in gentile Europeans in several generations, but still much of them can be detected through autosomal matches.

  10. On a side topic to this, and I’d be interested in anyone’s views, I was wondering if a Greg Clark style surname analysis could help on the issue of urban mortality or urban differential fertility rates? There are some good databases of where surnames could be found in Britain in 1500 (probably not as good data as the 1851 census, but good), and we might be able to find those disproportionately in London. If the theory that urbanites generally died and countryfolk repopulated the cities holds true, we should find that London surnames from 1500 are relatively rarer than we’d expect in London today, in contrast with long persistence elsewhere in Britain (https://www.nature.com/articles/s41467-021-26185-z“The vast majority of family names (in Britain) are…concentrated around the locales in which they were first coined between the 12th and 14th centuries”).

    (On a personal note I’m thinking a bit about my mother’s surname, which is Huguenot in origin, and still found in family based in and around London hundreds of years later, after the Huguenot migration presumably brought it to London. But how disproportionate is that survival relative to the migration? It seems like surnames would be a good quantitative way to talk about the degree to which urban populations left descendents.)

  11. Some other ways that we could look at this as well as surnames are more directly genetic.

    Like IBD segments taking advantage of the massive UK Biobank – https://bmcbiol.biomedcentral.com/articles/10.1186/s12915-021-00964-y

    Interestingly, drastic regional variations of preferences of local connectivity were shown. In Greater London, people with the weakest local connectivity are found, reflecting its cosmopolitan status. In Greater Manchester, people with moderate enrichment of local connectivity are found, indicating regional demographic movement in central England. In the major cities of Scotland and Wales, people with strong local connectivity are found.

    So that might imply that in London people’s ancestors don’t coalesce too much – which would make sense with a theory that the city sees particularly high levels of migration from the country – but on the other hand, there’s a lot more strong enrichment in Scottish and Welsh cities, which would be more indicative of the growth off the population naturally with the city (or alternatively but more complex, the city populated by single mass migrations from another area that somehow left no trace in its origin; not very likely). So less consistent with cities showing always a lack of natural population growth…

    Note that they don’t actually just look at samples from cities but across the UK, so it’s the cities in Scotland and Wales that show this more dramatic local connectivity, in contrast to not just London but country regions across Britain.

    Another check might be y-dna and mtdna coalescence over the last 500 years; if people with urban birth and residence locations tend to have fewer ancestors locally that coalesce 500 years ago, then that’s indicative of mobility into the city. Mutations on y and mtdna have a less predictable rate but with large enough sample sizes it presents another check.

    The Roman dna here is good, but I do think there need to be more checks to more explicitly establish how much local geneaological continuity and population growth there has been in city regions over time. Roman dna discontinuities can have other explanations than death rates – back when the British Empire largely ended / declined, a fair number of people moved back to England, and there might be similarities with the end / decline of the Roman Empire… Just a really interesting topic.

  12. The open thread is closed so I thought of posting this comment here.

    “Eventually, the Neanderthals gave way to modern humans even in this last redoubt, and the newcomers developed cultures of great sophistication, culminating in the last great Paleolithic hunter-gatherer societies of Europe west of the Rhine, the Magdalenian mammoth hunters.”

    Magdalebians were better known for their Mammoth art than for Mammoth hunting. Mammoths weren’t common Magdalenian prey. Deers and Reindeers were much more common prey and more characteristic for Magdalenians.

  13. A city isn’t an undifferentiated mass of people. I believe some analysis showed that modern Britons are mostly the descendants of the medieval middle class or above.

    So it’s more accurate to say the lower classes (urban and otherwise) died off.

    In China, by the time the Han dynasty ended, there were 200 thousand male descendants of Liu Bang, the founder of the Han dynasty, or almost 1% of the Chinese population at that time. By now, about 2% of the Chinese population are direct male line descendants of Liu Bang. When he founded the Han dynasty, Liu was a relatively rare Chinese surname. He (and the rest of his Han dynasty descendants) managed to make Liu one of the top 5 Chinese surnames. There are more Liu’s in the world than there are French people.

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