The paper, which was published in the journal 'Proceedings of the Royal Society B', aims to explain the high number of Germanic male-line ancestors found in modern-day England and showed that a relatively small immigrant Anglo-Saxon population (made up of invaders from present day Germany, Holland and Denmark) could have changed the face of British gene pool simply by using their economic advantage during apartheid to out-breed the Brits.

In less than fifteen generations the gene pool in what is now England was made up of over 50 per cent Germanic Y-chromosomes.

Dr Mark Thomas, of the UCL Department of Biology, said: "The native Britons were genetically and culturally absorbed by the Anglo-Saxons over a period of as little as a few hundred years.

"An initially small invading Anglo-Saxon elite could have quickly established themselves by having more children who survived to adulthood, thanks to their military power and economic advantage.

"We believe that they also prevented the native British genes getting into the Anglo-Saxon population by restricting intermarriage in a system of apartheid that left the country culturally and genetically Germanised. This is exactly what we see today - a population of largely Germanic genetic origin, speaking a principally German language."

According to the research, Anglo-Saxon settlers enjoyed a substantial social and economic advantage over the native Britons who lived in what is now England, for more than 300 years from the middle of the fifth century. In this society, people lived together in a servant-master relationship in a system akin to the apartheid system more recently found in South Africa.

Evidence of an ethnic divide can be found in ancient texts such as the laws of Ine. In around the seventh century these laws put a far greater value on the life of an Anglo-Saxon than on that of a native Briton (known as Welshman by the Anglo-Saxons at the time). If an Anglo-Saxon was killed the 'blood money' or 'Wergild' payable to the family was between two and five times more than the fine payable for the life of a Welshman.

In the paper, Dr Thomas and colleagues at the University of Reading and Imperial write: "This ethnic distinction of two intermingling populations and its formalisation in law cannot have survived for such a long period without some mechanism that perpetuated a distinction. Physical segregation could have had this effect, but this is not what the laws of Ine imply; therefore an apartheid-like social structure seems to be the most obvious mechanism."

Just how important a role migration played in the Anglo-Saxon takeover of Britain has been controversial for decades. Archaeological and historical evidence is inconclusive but points to a relatively small number of Anglo-Saxon migrants who are unlikely to have had the major impact on today's English gene pool that recent studies of the Y-chromosome reveal.

Statistical analysis carried out by Dr Thomas and colleagues in previous studies suggested that the English gene pool was made of between 50 and 100 per cent Anglo-Saxon Y-chromosomes. Most archaeologists had difficulty accepting this because their evidence pointed to a relatively small Anglo-Saxon immigrant population.

"Current estimates put the number of Anglo-Saxons migrating into England between the 5th and 7th century AD at between 10,000 and 200,000 immigrants, while the native population at that time was more than two million.

This study used computer simulations to show that an apartheid-like society explains the discrepancy between the archaeologist's and the geneticist's view.

Dr Mark Thomas said: "We modelled the Anglo-Saxon and native British populations to see what happened after a small number of Anglo-Saxons invaded. By testing a number of different combinations of ethnic intermarriage rates and the reproductive advantage of being Anglo-Saxon, we found that under a very wide range of different combinations of these factors we would get the genetic and linguistic patterns we see today.

"We put an idea that comes from historical research about apartheid into a computer model and have been able to show that the archaeologists and geneticists were both right. The disagreement can be settled by our finding that an apartheid-like society was set up by the invaders around 1600 years ago."

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