A preprint on some ancient DNA work in England is up. Researchers sequenced samples from seven early and middle Anglo-Saxon period and three late Iron Age (presumably Celtic) skeletons.
We generated a principal component plot of the ten ancient samples together with relevant European populations selected from published data 10,11 (Extended data Figure 3). The ancient samples fall within the range of modern English and Scottish samples, with the Iron Age samples from Hinxton and Linton falling closer to modern English and French samples, while most Anglo-Saxon era samples are closer to modern Scottish and Norwegian samples. Overall, though, population genetic differences between these samples at common alleles are very slight.
While principal component analysis can reveal relatively old population structure, such as generated from long-‐term isolation-‐by-‐distance models 12 , whole genome sequences let us study rare variants to gain insight into more recent population structure. [. . .]
There are striking differences in the sharing patterns of the samples, illustrated by the ratio of the number of rare alleles shared with Dutch individuals to the number shared with Spanish individuals (Figure 2a). The middle Anglo-‐Saxon samples from Hinxton (HS1, HS2, HS3) share relatively more rare variants with modern Dutch than the Iron Age samples from Hinxton (HI1, HI2) and Linton (L). The early Anglo-‐Saxon samples from Oakington are more diverse, with O1 and O2 being closer to the middle Anglo-‐Saxon samples, O4 exhibiting the same pattern as the Iron Age samples, and O3 showing an intermediate level of allele sharing, suggesting mixed ancestry. The differences between the samples are highest in low frequency alleles and decrease with increasing allele frequency. This is consistent with mutations of lower frequency on average being younger, reflecting more recent distinct ancestry, compared with higher frequency mutations reflecting older shared ancestry.
Comparing the relative number of rare alleles shared with the Dutch and Spanish samples, the researchers estimate 30% Anglo-Saxon admixture in the present-day East English and 20% in the Scottish and Welsh.
We also examined using the same method 30 modern samples from the UK10K project 16 , 10 each with birthplaces in East England, Wales and Scotland. Overall, these samples are closer to the Iron Age samples than to the Anglo-‐Saxon era samples (Figure 2a). There is a small but significant difference between the three modern British sample groups, with East English samples sharing slightly more alleles with the Dutch, and Scottish samples looking more like the Iron Age samples. To quantify the ancestry fractions, we fit the modern British samples with a mixture model of ancient components, by placing all the samples on a linear axis of relative Dutch allele sharing that integrates data from allele counts one to five (Figure 2b). By this measure the East England samples are consistent with 30% Anglo-‐Saxon ancestry on average, with a spread from 20% to 40%, and the Welsh and Scottish samples are consistent with 20% Anglo-‐Saxon ancestry on average, again with a large spread (Supplementary Table 2). An alternative and potentially more direct approach to estimate these fractions is to measure rare allele sharing directly between the modern British and the ancient samples. While being much noisier than the analysis using Dutch and Spanish outgroups, this yields consistent results (Extended Data Figure 4 and Supplementary Table 2). In summary, this analysis suggests that only 20-‐30% of the ancestry of modern Britons was contributed by Anglo-‐Saxon immigrants, with the higher number in East England closer to the immigrant source. The difference between the three modern groups is surprisingly small compared to the large differences seen in the ancient samples, although we note that the UK10K sample locations may not fully reflect historical geographical population structure because of recent population mixing.I have not thought about it deeply, but the rare variant comparison method used by the authors seems like it should produce reasonable results, at least for the relatively straightforward admixture estimates (with the understanding that Anglo-Saxons and Iron Age Britons are not the only two possible source populations for the modern British). I will say I was surprised to see Britain sharing a branch with Finland in this plot (even though it's a short one) to the exclusion of Denmark and Netherlands:
I've seen a few people interpret this study's estimates as a vindication of the ridiculous admixture estimates featured in the People of the British Isles project paper. For me, the ancient DNA results confirm my initial impression: the methods the POBI authors used to generate their estimates of ancient admixture were useless for divining what they thought they could divine.
That this 30% estimate informed by ancient DNA falls within the range of estimates suggested by the POBI authors is primarily a testament to the extremely broad range of possible admixture estimates they offered up (spanning 10% to 50%, depending on what one subjectively deemed "likely"). The POBI authors themselves were pushing for ~10% Anglo-Saxon admixture in the 19th-century Central and South English population (and if I recall correctly ~0% in the Welsh). POBI volunteers were primarily middle-aged or older people who could document four grandparents all born in particular locations. The UK10K modern British samples appearing in the ancient DNA paper are not screened in a similar manner, but are simply classified based on the sample donor's birth place. This means at least a couple generations (and probably disproportionately important generations, at that, as concerns mobility) of additional homogenization will have taken place.
So I have little doubt POBI samples from East Anglia (proxies for 19th-century East Anglians) would produce higher estimates of Anglo-Saxon admixture than "East England" UK10K samples (though apparently at present only microarray data, and not the whole genome sequencing data that would be necessary for the rare variant comparisons, is available for POBI samples). Levels up to 40% or higher Anglo-Saxon admixture in 19th-century East Anglians would not surprise me. And whatever the 19th-century number turns out to be, Anglo-Saxon admixture in England likely would have been progressively higher going back in time toward before the Norman conquest.
Gene flow into England over the past millennium (from Wales, Scotland, Ireland, and France) will have tended to make the English look less Anglo-Saxon and more "Iron Age". The Scandinavian component in the Normans and particularly their followers was probably outweighed by the French; and subsequently France probably remained one of the main sources of continental immigrants into England at least down to the Huguenots. It's said around 50,000 Huguenots came to England (against a 17th-century English population of around 5 million). 1% does not sound like an especially large wave (and it's certainly not by the standards of modern mass immigration), but these immigrants were concentrated in south and east England:
Huguenot settlement was concentrated in London and the south, East Anglia and the FensEven a relative trickle of continental immigrants over the past 1000 years might have had a noticeable cumulative effect on the English gene pool, and Scottish, Welsh, and Irish gene flow into England over the past millennium is likely even more significant. 24% of British claim Irish ancestry recent enough to be aware of, including 77% of those in London. Around 10% of the UK population is estimated to have an Irish grandparent.
Filtering recent Irish immigration into Scotland might also lead to higher estimates of Anglo-Saxon admixture there, as well (though recent English immigration too would need to be excluded). Recent English immigration into Wales may mean the 20% Anglo-Saxon admixture estimate is significantly inflated (though going off the 20% estimate for modern Welsh I would guess 19th-century Welsh speakers had at least ~10% Anglo-Saxon-like admixture).
According to the authors:
The genetic analyses described above add significantly to our picture of Anglo-Saxon migration into Britain. In the cemetery at Oakington we see evidence even in the early Anglo-Saxon period for a genetically mixed but culturally Anglo-Saxon community 21,22 , in contrast to claims for strong segregation between newcomers and indigenous peoples 7 . The genomes of two sequenced individuals are consistent with them being of recent immigrant origin, from different continental source populations, one was genetically similar to native Iron Age samples, and the fourth was an admixed individual, indicating intermarriage. Despite this, their graves were conspicuously similar, with all four individuals buried in flexed position, and with similar grave furnishing. Interestingly the wealthiest grave, with a large cruciform brooch, belonged to the individual of native British ancestry (O4), and the individual without grave goods was one of the two genetically “foreign” ones (O2), an observation consistent with isotope analysis at West Heslerton which suggests that new immigrants were frequently poorer 23,24 . Given this mixing apparent around 500CE, and that the modern population is no more than 30% of Anglo-Saxon ancestry, it is perhaps surprising that the middle Anglo-Saxon individuals from the more dispersed field cemetery in Hinxton all look genetically consistent with unmixed immigrant ancestry. One possibility is that this reflects continued immigration until at least the Middle Saxon period.In fact, there's nothing really inconsistent with the "Anglo-Saxon apartheid" paper in the mixed earlier samples and unmixed later samples. The Anglo-Saxon period samples tested here are all female. It's easy to imagine intermarriage rates may have been higher among the earliest Anglo-Saxon settlers, when their fraction of the total British population would have been smallest -- especially if females were to any degree underrepresented among the incoming Anglo-Saxons.
From the "Anglo-Saxon apartheid" paper (Evidence for an apartheid-like social structure in early Anglo-Saxon England):
We have only considered the effects of differences in ethnic reproductive advantage and inter-ethnic marriage rate on patterns of genetic variation. If there were no sex bias in the intermarriage rate, then we would expect these effects to be equal for the different genetic systems (mitochondrial DNA, Y-chromosome, X-chromosome, autosomes). However, part of the motivation for this study was to seek an explanation for the discrepancy between archaeological estimates of the size of the Anglo-Saxon migration (Härke 1998, 2002; Hills 2003) and estimates based on Y-chromosome data (Weale et al. 2002; Capelli et al. 2003). There are three further factors that could exacerbate replacement of indigenous Y-chromosomes. The first is that when intermarriage does occur the offspring may be more likely to assume the identity of the father, thus reducing the effective intermarriage rate, as it would affect patterns of Y-chromosome diversity. The second is that forced extra-marital matings are more likely to occur between Anglo-Saxon men and native British women than the reverse since, as the law codes of Ine indicate, the degree of punishment was determined by the social status of the victim. The third is based on the theory that relatively ‘good condition’ males tend to out-reproduce females of a similar condition, whereas relatively ‘poor condition’ females tend to out-reproduce their male counterparts (Trivers & Willard 1973). From this, a strategy of sex-biased parental investment, whereby relatively wealthy parents favour wealth transfer to their sons, should emerge (Hartung 1976). Such a phenomenon is supported by genealogical data (Boone 1986) and should lead to an asymmetric increase in the population frequency of Y-chromosomes carried by wealthy men, when compared to the other genetic systems.
The motivation for this study was to reconcile the discrepancy between, on the one hand, archaeological and historical ideas about the scale of the Anglo-Saxon immigration (Hills 2003), and on the other, estimates of the genetic contribution of the Anglo-Saxon immigrants to the modern English gene pool (Weale et al. 2002; Capelli et al. 2003). We have shown that this discrepancy can be resolved by the assumption of an apartheid-like social structure within a range of plausible values for interethnic marriage and socially driven reproductive advantage following immigration (Woolf 2004). Perhaps most strikingly, our model indicates that, by using plausible parameter values, the genetic contribution of an immigrant population can rise from less than 10% to more than 50% in as little as five generations, and certainly less than fifteen generations. Similar processes are likely to have shaped patterns of genetic variation in other ‘conquest societies’ of the period, and perhaps more recently (Carvajal-Carmona et al. 2000).