By constructing the first fine-scale map of the British Isles, Oxford University researchers have uncovered distinct geographical groupings of genetically similar individuals across the UK.
The study, published in the journal Nature, found that:
- There was no single 'Celtic' genetic group. In fact the Celtic parts of the UK (Scotland, Northern Ireland, Wales and Cornwall) are among the most different from each other genetically. For example, the Cornish are much more similar genetically to other English groups than they are to the Welsh or the Scots.
- There are separate genetic groups in Cornwall and Devon, with a division almost exactly along the modern county boundary.
- The majority of eastern, central and southern England is made up of a single, relatively homogeneous, genetic group with a significant DNA contribution from Anglo-Saxon migrations (10-40% of total ancestry). This settles a historical controversy in showing that the Anglo-Saxons intermarried with, rather than replaced, the existing populations.
- The population in Orkney emerged as the most genetically distinct, with 25% of DNA coming from Norwegian ancestors. This shows clearly that the Norse Viking invasion (9th century) did not simply replace the indigenous Orkney population.
- The Welsh appear more similar to the earliest settlers of Britain after the last ice age than do other people in the UK.
- There is no obvious genetic signature of the Danish Vikings, who controlled large parts of England ('The Danelaw') from the 9th century.
- There is genetic evidence of the effect of the Landsker line – the boundary between English-speaking people in south-west Pembrokeshire (sometimes known as 'Little England beyond Wales') and the Welsh speakers in the rest of Wales, which persisted for almost a millennium.
- The analyses suggest there was a substantial migration across the channel after the original post-ice-age settlers, but before Roman times. DNA from these migrants spread across England, Scotland, and Northern Ireland, but had little impact in Wales.
- Many of the genetic clusters show similar locations to the tribal groupings and kingdoms around end of the 6th century, after the settlement of the Anglo-Saxons, suggesting these tribes and kingdoms may have maintained a regional identity for many centuries.
The study uses data from the Wellcome Trust-funded People of the British Isles study, an Oxford University project which has collected blood samples from about 4,500 volunteers from rural regions throughout the UK. Sir Walter Bodmer from Oxford University, who conceived the project and co-led the work said: 'The People of the British Isles study gave us a wonderful opportunity to learn about the fine-scale genetic patterns in the UK population. A key part of our success was collecting DNA from a geographically diverse group of people who are representative of their location. We are very grateful to all the volunteers who participated in the study.'
An international research team (including scientist from University College London and Australia's Murdoch Childrens Research Institute) analysed DNA samples from more than 2,000 of these volunteers to create the first fine-scale genetic map of a whole country.
All four grandparents of the volunteers selected in this study were born within 80 km of each other. Because grandparents contribute a quarter each to their descendants genome, focussing on this group of volunteers means that the researchers were effectively sampling DNA from the volunteers’ ancestors, allowing a snapshot of UK genetics in the late 19th Century.
To uncover the extremely subtle genetic differences among these individuals, the researchers used cutting-edge statistical techniques, developed by four of the team members. Using these statistical techniques (called fineSTRUCTURE and GLOBETROTTER), the team were able to separate the DNA samples into genetically similar individuals, without knowing where in the UK the samples came from. By plotting each person onto a map of the British Isles, using the centre point of their grandparents' birth places, they were able to see how this distribution correlated with their genetic groupings.
By comparing this information with DNA samples from over 6,000 Europeans, the team identified clear traces of population movements into the UK over the past 10,000 years. Professor Peter Donnelly, Director of the Wellcome Trust Centre for Human Genetics, who co-led the research, said: 'It has long been known that human populations differ genetically, but never before have we been able to observe such exquisite and fascinating detail. By coupling this with our assessment of the genetic contributions from different parts of Europe we were able to add to our understanding of UK population history.'
The researchers were then able to 'zoom in' to examine the genetic patterns in the UK at levels of increasing resolution. At the broadest scale, the population in Orkney (islands to the north of Scotland) emerged as the most genetically distinct. At the next level, Wales forms a distinct genetic group, followed by a further division between north and south Wales. Then the north of England, Scotland, and Northern Ireland collectively separate from southern England, before Cornwall forms a separate cluster. Scotland and Northern Ireland then separate from northern England. The study eventually focused at the level where the UK was divided into 17 genetically distinct clusters of people.
Professor Mark Robinson, an archaeologist on the project from the Oxford University Museum of Natural History, said 'The results give an answer to the question we had never previously thought we would be able to ask about the degree of British survival after the collapse of Roman Britain and the coming of the Saxons.'
Source: The Wellcome Trust
A report of the research, entitled 'The fine- scale genetic structure of the British population', is published in Nature.