An Italian-led study has traced the origins of the first inhabitants of the Americas.

The study, led by geneticists at Pavia University, tracked two rare strings of DNA stored in the world's largest genealogical bank and found that two distinct groups travelled from Asia about 15,000 years ago.

''One group came into North America on the Beringia land bridge but the other went all the way down the Pacific, right down to the tip of South America - which explains the startling difference in their present-day heirs,'' Pavia geneticist Antonio Torroni told the journal Current Biology.