An extraordinary DNA project run by Oxford scientists has mapped out the DNA of the Peoples of the British Isles – Judith Keeling explains.

What makes us British? Do the English, Welsh, Irish and Scots have much in common at all? And how different are we from our European neighbours?

These topical questions – hot potatoes in political debates ranging from potential Scottish independence to Britain’s role in the European Union – have now also been probed at the most fundamental level of all in ground-breaking research by an eminent team of Oxford researchers. The team, led by Oxford geneticist Professor Sir Walter Bodmer, has conducted a detailed and wide-ranging study of the genetic make-up of the Peoples of the British Isles (PoBI). Fascinatingly, their findings show that most people living in the British Isles are fundamentally extremely similar, genetically-speaking at least.

Where small, but marked, DNA differences do exist the researchers found they naturally clustered geographically – long predating the invention of county boundaries – despite the fact that analysis of the results took no account of where the samples had originated. Moreover, genetically speaking the average Briton has a great deal more in common with our French and German partners in Europe than some might currently like to think.

“It was always intended that we would look in some detail at the potential genetic differences to be found in the people of the British Isles because no survey like this had ever been done before,” says Professor Peter Donnelly, Director of the Wellcome Trust Centre for Human Genetics and professor of statistical science at Oxford. Donnelly led the application of the sophisticated statistical techniques used to tease information out of the vast body of data collected. He also led the analysis of the results.

Effectively, after a five-year research programme involving nearly 4,000 blood samples from around the British Isles, the PoBI team produced a sort of DNA equivalent of the Domesday Book for the new millennium – a detailed genetic inventory of exactly what makes up the British.

The profound implications of the Oxford team’s work for future medical research are obvious. Data obtained from the PoBI research, funded by the Wellcome Trust, effectively forms a ‘control’ sample that can be used in the future to compare against the DNA composition of people suffering from a range of diseases from diabetes to cancer. “By obtaining a good genetic definition of the British population, this can be used in future research into the genetic components of susceptibility to a number of diseases,” explains Bodmer. But the PoBI genetic mapping project has also yielded highly significant results for archaeologists, with one leading Oxford archaeologist hailing it as “the most exciting discovery in Anglo-Saxon history in the past ten years.”

The analysis of the PoBI data has, says Professor Mark Robinson, helped to conclude one of the most fiercely debated questions in Anglo-Saxon history: what happened to the native Romano-British population when the Angles, Saxons and Jutes invaded following the fall of the Roman Empire in Britain?

Archaeological evidence from sources such as pottery fragments suggest that the Romano-Britons (the population left living in the UK when the Romans left) were virtually extinguished and replaced by the Anglo-Saxons in a short space of time. But what really happened? “Genetical evidence such as this gives us information about what happened to the whole population – the small man, not just the leaders and the elites that history and archaeology tend to focus on,” says Bodmer.

There have been a number of theories over the years as to what happened to the Romano-British population, says Robinson, an environmental archaeologist. One is that the Romano- British population was physically driven westwards to Cornwall and Wales out of the south-eastern and central portion of Britain which had been colonised by the Romans. “It has also been suggested that a small Anglo-Saxon elite arrived that somehow persuaded the Romano-British population to adopt their culture, customs and language,” says Robinson. Other theories have involved a virtual genocide of the Romano-Britons by the invading Anglo-Saxons.

However, the PoBI evidence points firmly to a large influx of Anglo-Saxon DNA but also the presence in modern descendants of a substantial amount of an ‘ancient British’ DNA which most closely matches the DNA of modern inhabitants of France and Ireland. This led the researchers to conclude that there had been an intermingling between the existing Romano-British population and the newcomer Anglo- Saxons, rather than a full-scale population wipe-out.

So how did the Oxford researchers arrive at their results? One key element of the project’s success was its painstaking collection of samples. These were taken from volunteers living in rural areas where all four grandparents had been born in the same area. This ensured that the samples were more likely to be locally representative. Effectively, the data gave an accurate picture of the genetic makeup of rural Britain in around 1880, before the wide-scale population movements of the 20th century or, more recently, immigration from other countries. “In order to really understand the British population genetically, you can’t just go into the high street and look for someone who says they are British. You need to be more specific about where you look,” says Bodmer.

Another vital point was the team’s ability to measure a large amount of genetic material from each sample. More than 670,000 positions in the genome of each individual were measured and evaluated by Donnelly and his team in order to produce a precise picture of that person’s genetic make-up. Sophisticated statistical techniques were then applied to sift and analyse the relevant data from this vast body of information.

The volunteer samples were analysed for ways in which their DNA was similar to each others’. They were then grouped according to their genetic similarities. The final results were then laid on top of a map of the British Isles… with astounding results.

“It is simply not the case that we have seen what we expected to see,” says Robinson. “I feel we’ve produced something which is of major significance and will stimulate much debate.”

“Broadly speaking, people look very similar to each other at the DNA level from one end of the UK to the other, so the differences we found were subtle but nonetheless real,” says Donnelly. “However, we were struck by how clear the patterns of regional differences were, by how people had stayed in their geographic regions. Clearly, in some areas there had been quite a bit of isolation and relatively little intermarriage over the years.” When the data was first split, into two groups, it was the inhabitants of Orkney who were most different from the rest of the British Isles.

The researchers continued to break down the data, using increasingly fine distinctions between the samples. Wales broke away, then Cornwall and Devon; the Welsh borders separated from Wales, and Northern Ireland formed a group with north western Scotland; Northern England also split away.

By the final analysis, there were 17 cluster groups (see map) with north and south Wales showing two very separate clusters. There were also two distinct groups in the Orkney Islands. But by far the biggest homogeneous region was a large swathe of southern and central England (pictured in red on the map). The researchers then compared their PoBI results with DNA data from 7,000 people in Europe to try to trace the ancestry of the British DNA.

It was clear that the Orkney islanders had Norwegian ancestors, while the red central and southern English cluster had the largest Belgian, Danish and German contribution (relating to the Anglo-Saxon invasion and perhaps later supplemented in places by the Vikings). The Cornish and Welsh had more similarity with the modern French, while people in Northern Ireland and Western Scotland have substantial common Irish ancestry.

“We can see clear signs of certain patterns which are present in the DNA of samples from all over the British Isles – this means that they are likely to be very old, and is what we have termed the ancient British DNA,” says Donnelly. Researchers agree that the DNA evidence fits the known colonisation patterns of early settlers to the British Isles after the Ice Age between 9,600 and 8,000 BC. The first settlers made their way across to the warming tundra that was then the British Isles from North-West Europe via the land bridge that still attached the UK to the area that is now the Low Countries.

Others came by boat from the Atlantic coast of France to the western side of England and Wales and Ireland. This is clearly reflected in the similarities to French and probably Belgian DNA in southern and central England, and the increased level of western French DNA in Cornwall and Wales. So our ancient British DNA has deep roots on the continent – and particularly in France. For the large section of the population living in the red section of southern and central England, their DNA contained substantial contributions from both the ancient British and the Anglo-Saxons. It is this that has led the researchers to conclude that although the Romano- British people were certainly overwhelmed by a large influx of Anglo-Saxons, they were not annihilated by them, but married and mixed with the newcomers. Equally it’s clear from the PoBI results that both the Roman and Norman invasions left relatively little genetic trace in Britain, being restricted to a relatively small number of elite rulers.

“One of the most rewarding aspects of this project has been the way that academics from different departments of the university – geneticists, statisticians and archaeologists – have collaborated and pooled their expertise,” says Robinson.

But the researchers are far from resting on their laurels. Bodmer and Donnelly are now involved in a new project to understand exactly how our genes control the make-up of our facial features. Could this, for instance, lead to police giving out descriptions of wanted individuals based on DNA samples from crime scenes? “It’s possible, in the very distant future, I suppose,” says Donnelly, “but we’re really a very long way from that at the moment.”

Meanwhile, back in the archaeology department, there are plans to compare the modern PoBI findings with ancient DNA samples from skeletal remains in Anglo-Saxon graveyards. “I believe that this will back up our interpretations… but if it doesn’t, well, that’s how progress is made,” says Robinson.

And there’s also much more work to be done in understanding the DNA make-up of European populations and to extend the PoBI research to southern Ireland. One thing’s for sure, however: and that’s that after the conclusions of this project are finally published, many areas of academic research will never be the same again.

Judith Keeling is a freelance writer and editor contributing to a wide range of national newspapers and magazines. She is editor of Oxfordpeople, an interactive community website.