Cultural differences which divide the Scots and the English date back 10,000 years before Britain was an island, a professor has suggested.
Are Anglo-Scottish differences greater than we thought?
Stephen Oppenheimer, of Oxford University, says genetic evidence shows Celts descended from ancient people living by the Atlantic coast.
The English are more closely related to Germanic people, he added.
The professor was due to speak about his theory at the Edinburgh Science Festival on Sunday.
In the past, the split was attributed to migration, invasion and replacement, in particular by the Anglo-Saxons, Celts and Vikings.
However, while conceding foreign invasions hundreds of years ago would have influenced the cultures in different areas, he does not believe the split originated then.
Professor Oppenheimer said: "The first line between the English and the Celts was put down at a much earlier period, say 10,000 years ago.
"The English are the odd ones out because they are the ones more linked to continental Europe.
"The Scots, the Irish, the Welsh and the Cornish are all very similar in their genetic pattern to the Basque."
This would mean Celts' roots lie in south west France, Brittany and Spain.
The theory is expanded in the professor's book The Real Eve: Modern Man's Journey Out Of Africa, tracing the origins of humankind to Africa 80,000 years ago.
The talk called Out of Eden takes place at the Apex International Hotel in Grassmarket on Sunday.