British origins (Leslie et al. 2015)

The long-awaited paper on the People of the British Isles has just appeared in Nature. I will update this entry with more information.

UPDATE:

The authors write:

Consistent with earlier studies of the UK, population structure within the PoBI collection is very limited. The average of the pairwise FST estimates between each of the 30 sample collection districts is 0.0007, with a maximum of 0.003 (Supplementary Table 1).

These are extremely small differences in the European (let alone global) context. So, the British are, overall, a very homogeneous population. This is what led the researchers to use methods such as ChromoPainter/ fineStructure/ Globetrotter that can squeeze out fine-scale population structure by exploiting linkage disequilibrium. Thus, the authors are able to detect 17 main clusters of the British.

Most of the clusters are geographical, but some span different regions (e.g., the "yellow circle" cluster). The elephant in the room is the "red square" cluster which spans Central/South England. The authors write:

There is a single large cluster (red squares) that covers most of central and southern England and extends up the east coast. Notably, even at the finest level of differentiation returned by fineSTRUCTURE (53 clusters), this cluster remains largely intact and contains almost half the individuals (1,006) in our study.

The authors then tried to infer the ancestry of the British clusters in terms of continental European clusters, which is to be published separately. In the plot on the right, you see the British clusters (columns) and their continental European sources (rows). The authors observe that clusters that are widely represented in Britain are likely to be older, while those that are missing in some populations are likely to be younger, because they didn't have the chance to spread across Britain. For example, a couple of Norwegian clusters are strongly represented in the Orkney islands, and these are likely to reflect Viking colonization.

The authors draw conclusions on several historical episodes of British history. The big one is the extent of Anglo-Saxon ancestry:

After the Saxon migrations, the language, place names, cereal crops and pottery styles all changed from that of the existing (Romano-British) population to those of the Saxon migrants. There has been ongoing historical and archaeological controversy about the extent to which the Saxons replaced the existing Romano-British populations. Earlier genetic analyses, based on limited samples and specific loci, gave conflicting results. With genome-wide data we can resolve this debate. Two separate analyses (ancestry profiles and GLOBETROTTER) show clear evidence in modern England of the Saxon migration, but each limits the proportion of Saxon ancestry, clearly excluding the possibility of long-term Saxon replacement. We estimate the proportion of Saxon ancestry in Cent./S England as very likely to be under 50%, and most likely in the range of 10–40%.

Two other details are the lack of Danish Viking ancestry in England:

In particular, we see no clear genetic evidence of the Danish Viking occupation and control of a large part of England, either in separate UK clusters in that region, or in estimated ancestry profiles, suggesting a relatively limited input of DNA from the Danish Vikings and subsequent mixing with nearby regions, and clear evidence for only a minority Norse contribution (about 25%) to the current Orkney population.

And, the absence of a unified pre-Saxon "Celtic" population. What seems to unify "Celts" is lower levels/absence of the Saxon influence, rather than belonging to a homogeneous "Celtic" population:

We saw no evidence of a general ‘Celtic’ population in non-Saxon parts of the UK. Instead there were many distinct genetic clusters in these regions, some amongst the most different in our study, in the sense of being most separated in the hierarchical clustering tree in Fig. 1. Further, the ancestry profile of Cornwall (perhaps expected to resemble other Celtic clusters) is quite different from that of the Welsh clusters, and much closer to that of Devon, and Cent./S England. However, the data do suggest that the Welsh clusters represent populations that are more similar to the early post-Ice-Age settlers of Britain than those from elsewhere in the UK.

Unfortunately, the authors have decided not to make their data publicly available. This is very unfortunate, and will keep this research out of the hands of many people who would be interested in it and who would be interested in analyzing this data. I can already guess the disappointment of people of British ancestry from around the world who have a genealogical interest in tracing their British ancestors to particular areas of the UK. Apparently, the data is deposited in the EGA archive, access requires red tape, and is apparently limited to institutional researchers. Thus, this data, perhaps the richest genetic survey of any country to date, will not be fully utilized to further science.

Nature 519, 309–314 (19 March 2015) doi:10.1038/nature14230

The fine-scale genetic structure of the British population

Stephen Leslie et al.

Fine-scale genetic variation between human populations is interesting as a signature of historical demographic events and because of its potential for confounding disease studies. We use haplotype-based statistical methods to analyse genome-wide single nucleotide polymorphism (SNP) data from a carefully chosen geographically diverse sample of 2,039 individuals from the United Kingdom. This reveals a rich and detailed pattern of genetic differentiation with remarkable concordance between genetic clusters and geography. The regional genetic differentiation and differing patterns of shared ancestry with 6,209 individuals from across Europe carry clear signals of historical demographic events. We estimate the genetic contribution to southeastern England from Anglo-Saxon migrations to be under half, and identify the regions not carrying genetic material from these migrations. We suggest significant pre-Roman but post-Mesolithic movement into southeastern England from continental Europe, and show that in non-Saxon parts of the United Kingdom, there exist genetically differentiated subgroups rather than a general ‘Celtic’ population.

Link