Previously historians had believed the Welsh were mainly made up of Celtic incomers from Europe a few centuries ago.
But study of DNA could now rewrite Welsh history.
The evidence is based on research into the spread of the Y-chromosome - the male chromosome passed from father to son.
The findings are revealed by the Welsh geneticist Steve Jones in his book, Y - The Descent Of Man.
His evidence is outlined in the autumn edition of the Welsh language magazine, Y Faner Newydd, by joint editor Emyr Llywelyn.
Mr Llywelyn explains that male chromosomes reveal the Welsh, the Basques, the Irish and Scots Gaelic, as well as a tribe called the Kets in Siberia, are all blood brothers.
He also claims the chromosomes reveal the Welsh were the original inhabitants of Britain and they suffered ethnic cleansing at the hands of the Saxon invaders after the Romans left Britain in the Dark Ages.
According to Steve Jones: "The Asian genetic signature links its bearers not only with the first Americans but, quite unexpectedly, with inhabitants of the western fringe of Europe."
