THE waves of invasion and immigration that have, from time to time, swept over the British Isles have led some to refer to Britons as a mongrel nation. A study just published in Nature by Peter Donnelly of Oxford University and his colleagues shows there is some truth in this, and that the palimpsest of those events is visible in people’s genes—or, at least, that it was still discernible in the late 19th century.

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.

The map is dominated by a DNA cluster that might reasonably be described as “English”. Comparison with continental Europe shows, as might be expected, that this English cluster is related to northern Germany, where the Anglo-Saxons came from—though the admixture is less than 50%, which indicates (again, as expected) that there was much interbreeding between interlopers and natives.

Others kept themselves to themselves. Yorkshiremen and women will be gratified to note that the west of their county clusters separately from the rest of England, and Lancastrians similarly horrified that Yorkshire’s tendrils extend into much of theirs. 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).

The whole so-called Celtic fringe, of areas in the west and north of Great Britain that were not invaded by the Saxons, is far more genetically diverse than its mythopoeic appellation suggests. Orkney, which has three clusters of its own, looks Norse. That is no surprise. It was, after all, part of Norway for 600 years. But north and south Wales are different from each other, and mainland Scotland has several clusters (two of which—a consequence, presumably, of the 17th-century plantations organised by King James VI and I—extend into Northern Ireland). The marcher lands between England and Scotland, and between England and Wales, harbour still further indigenous clusters.