Science: DNA shows how Thor Heyerdahl got it wrong

Fifty years ago, Thor Heyerdahl and the Kon-Tiki expedition appeared to prove that ancient humans could have sailed west from South American to colonise the Pacific islands. But DNA evidence now shows that his theory was wrong. Charles Arthur, Science Editor, on the molecules that have upset a great adventure.

In The Voyage of the `Kon-Tiki', the Norwegian archaeologist Thor Heyerdahl famously proved that early humans could have used the trade winds to sail from Peru to Easter Island - and thus be its first settlers. But although the tale of his replica raft and the voyage westward across the Pacific in August 1947 makes a stirring tale, his idea has now been proved to be wrong. Sorry, Thor: DNA analysis of the remains of the original settlers of islands all around the Pacific, including Easter Island, demonstrates that they actually came from South-East Asia.

Dr Erika Hagelberg, of the department of genetics at Cambridge University, has spent the past eight years studying the mitochondrial DNA - passed down through the maternal line - of Polynesians, who moved into the western Pacific about 1,500 years ago, and the Melanesians, who were the first to migrate there during the Pleistocene era about 60,000 years ago.

"There are two groups of populations which moved into the area, but both ultimately came from Asia," Dr Hagelberg said yesterday. "The Melanesians could have been one of the first migrations of modern humans out of Africa." They appear to have reached New Guinea, where they settled. The Polynesians then followed, and colonised New Zealand, Hawaii and Easter Island itself.

Determining the origins of populations by analysing mitochondrial DNA is done by first assuming that mutations in the sequence of the DNA arise at a specific rate but differently for different people. So two populations which evolve apart will have dissimilar sequences of mitochondrial DNA. That means you can distinguish where the DNA found in skeletons originated from, by comparing it with that from modern-day populations and also ancient DNA of known origins. And in the case of Easter Island's original settlers, it turns out that their common ancestor comes from South-East Asia - not South America.

Professor Heyerdahl has counter-claimed that the real first settlers cremated their dead, which would destroy any potential evidence. But Dr Hagelberg disputes this. "I can look at the DNA in the bones. I've examined a couple of hundred skeletons. It just takes patience and attention to detail."

Her work was done in collaboration with teams in Oxford, Holland and Australia and presented yesterday at a seminar at the Natural History Museum, organised by the Natural Environment Research Council, looking at "ancient biomolecules".