History on the map
Genetic Geography of Great Britain
Alexandra Bruter, <url>
The genetic map of Great Britain was compiled in their study by British scientists. In addition to the usual measurements for the map, longitude and latitude, there is also a third one on this map – time. The results of the research are published in the journal Nature (Leslie et al., The fine-scale genetic structure of the British population).
The growth of population mobility and urbanization has led to the fact that the analysis of the genomes of our randomly selected contemporaries cannot give a detailed picture of the settlement of their ancestors in the country. This is typical not only for the post-Soviet space, but also to a large extent for the UK. Therefore, the study participants were selected by the authors very carefully.
Only people living in rural areas could take part in the study. In addition, they had to meet a rather strict requirement: all their grandparents (all four people) had to be born no more than 80 km from each other. The average year of birth of grandparents turned out to be 1885 – the times of good old England and low mobility. The study involved 2,039 Britons. In addition, to restore the historical picture of the settlement of Britain, scientists used a ready-made database containing about 6,000 genomes of residents of other European countries.
The genetic diversity of Britons living in different parts of the island turned out to be small, but it still exists. Based on the analysis of single nucleotide polymorphisms (SNP) in the autosomes of Britons, it was possible to divide them into 17 clusters.
17 genetic clusters of the UK population (diagram from an article in Nature)
SNPs are mutations that usually do neither harm nor benefit. This means that they are not affected by selection and the probability of meeting them in the population remains approximately constant. But if a part of the population moves to a new place, it takes its SNPs with it. Analyzing them, it is easy to trace any mass movements of people. SNP, like any other mutations, occur all the time. It may turn out that a new polymorphism arose after the separation of the population in only one of the parts. By examining such cases, it is possible to determine which subpopulations are more closely related and separated recently, and which are more distant and separated a long time ago.
Autosomes are called all chromosomes except sex chromosomes – X and Y. Researchers of genetic history and geography often follow a simpler path – they study the Y chromosome and mitochondrial DNA. This path is simpler, because Y-chromosomes and mitochondrial DNA do not recombine, but are transmitted unchanged exclusively through male and female lines. This means that if an ancestor had some feature in these parts of the genome, then all descendants of the corresponding sex will have it. When studying autosomal SNPs, it should be borne in mind that, since chromosomes recombine, the transmission of SNP by inheritance is probabilistic. This makes it difficult to analyze the data, but the picture obtained in this way turns out to be more complete and accurate. For example, another small but bloodthirsty wave of conquerors (mostly men) can bring their Y chromosomes with them and successfully pass them on by inheritance. Analysis of the DNA of the Y chromosome several hundred years after the conquest will show that the territory is largely inhabited by close relatives of the conquerors, but in fact this is not quite true.
Any fragment of DNA is obtained by a person from one of his grandparents, there is nowhere else. Some modern kinship tests are based on this principle. If the SNP is found in a person in a given geographical area, his grandparents lived around the same place, then we can conclude that this SNP lived here already at the end of the XIX century. And this means that, with a high probability, he was here before.
So, the authors of the work divided all native Britons into 17 clusters. The most distant relatives of all other Britons were the inhabitants of the Orkney Islands. This is a group of islands lying to the north of Scotland, where only about 20 thousand people live. In addition, it turned out that these 20 thousand are well divided into as many as three groups. This is probably due to the existence of a natural water barrier. Then the inhabitants of Wales are separated from the common trunk, also then divided into three groups, occupying almost non-overlapping territories. It is noteworthy that the boundaries of modern administrative-territorial units coincided quite accurately with the boundaries of genetic clusters.
Distribution of continental ancestors (diagram from an article in Nature)
In order to recreate the historical picture based on the genomic data obtained, the authors analyzed a set of genomes of European residents and determined the degree of kinship with different European clusters for each British cluster. Some of the results were quite expected. For example, the inhabitants of the Orkney Islands were related to the Norwegians. This is not surprising: from 875 to 1472, the islands were part of Norway.
Other findings of the authors of the study look more unexpected. Although they found traces of the Saxon invasion of Great Britain in the genomes of modern Englishmen, it follows from their results that the influence of the Saxons on the ethnogenesis of the British people is greatly exaggerated. Even in regions where the Saxon component is most pronounced, it is no more than 20%. The authors almost failed to find traces of the conquest of these territories by the Danish Vikings.
Another remarkable result is that the authors failed to find any Celtic community in those parts of the country where the Saxons did not reach. Although, in theory, the whole island was inhabited by Celts, and the invading Saxons gradually moved inland from the southeast to the west and north, and Wales, Cornwall, Ireland and part of Scotland remained the last refuge of the Celts. In fact, the inhabitants of Wales and Cornwall differ much more than the inhabitants of Cornwall and, say, Devon. At the same time, some data really suggest that the Welsh clusters correspond to the most ancient inhabitants of the island.
Thanks to the careful selection of participants for the study and the masterly mastery of statistical methods, the authors of the work managed to compile a genetic map of the country with very high resolution. Interpreting the results, we were able to answer some questions that have long been the subject of controversy among historians. One such important question is the extent to which the Romano–British population was replaced by the Saxon population after the Saxon invasion. Although studies of material culture and language suggested that almost nothing remained of the pre-Saxon population, genetic studies refuted this assumption, showing that no more than half of the Saxon in the newly emerging ethnos turned out to be.
Portal "Eternal youth" http://vechnayamolodost.ru20.03.2015