Dr Donnelly’s team looked in detail at the DNA of 2,039 Britons from all parts of Great Britain and Northern Ireland, each of whose grandparents had all been born within 80km of each other. They thus, in effect, sampled the distribution of genetic material in the country in 1885 (the average year of the birth of these grandparents), before the large-scale internal population movements of the 20th century had had a chance to confuse the issue. The results divided into 17 genetic clusters, illustrated on the map, which form a pattern that conforms quite well with what an historian might have predicted, but with some interesting wrinkles.
Cornwall, too, clusters separately from England. Indeed, as all good Cornish would have suspected, it clusters separately even from Devon (which is itself also genetically different from England).
Full story in the Economist here: