In A.D. 410, Roman authority in Britain collapsed and Romano-British society disappeared from history under the invading tides of Angles and Saxons from northern Europe. Historians have been debating ever since whether the Romano-British were wiped out or survived by adopting their conquerors’ language and culture.

A fine-scale genetic analysis of the British population has now provided the answer. The invaders and the existing population lived side by side and eventually intermarried extensively. The people of south and central England are now genetically well mixed, with Saxon genes accounting for only about 20 percent of the mix, says a genetics team led by Stephen Leslie of the Murdoch Childrens Research Institute in Victoria, Australia, and by Peter Donnelly and Walter Bodmer of Oxford University.

The British Isles were wiped clean of people by the glaciers that descended toward the end of the last ice age, and were repopulated some 10,000 years ago by people who trekked over the broad land bridge that then joined eastern England to Europe north of the Rhine. The researchers say they can identify the genetic signature of this early migration, which survives most strongly in people from the western extremity of Wales.

Another strong genetic signal comes from the Orkney Islands north of Scotland. Some 25 percent of the DNA of Orcadians is of Norwegian origin, which is consistent with Norway’s long ownership of the islands.