DNA from long-lost lock of hair aids new Africa migration theory

Sep 24 2011 - 7:38am

SAN FRANCISCO -- Long, long ago, a bold race of early modern humans left Africa and migrated across vast stretches of southern Asia to Australia -- a mass migration of humankind that was followed thousands of years later by a second wave of African migrants who would settle all of Europe and the northern reaches of the Eurasian continent.

This new tale of humanity's movements out of Africa and around the world comes from an international team of geneticists who report they have traced the record of that first migration by sequencing the DNA from a single lock of hair of an unknown Australian Aborigine that had lain for nearly a century in a British museum.

The scientists maintain that instead of one human wave out of Africa, as has been traditionally believed, there must have been two. The first migration across southern Asia established the first Australians, the continent's Aboriginal population; the second migration, much later, saw modern humans, and, for a while, the Neanderthals, spread all across Europe and ultimately Asia.

That earlier migration took place more than 70,000 years ago, according to the geneticists, placing it at least 24,000 years before the second wave of humans that would later populate Europe, Asia and, eventually, America.

Although the numbers are imprecise, the findings seem to confirm what archaeologists have long maintained: that the ancestors of today's aboriginal Australians arrived there some 50,000 years ago -- although how they got there despite many ocean barriers remains a mystery.

A report on this elaborate feat of genetic detective work was published online in the journal Science Express by a group of nearly 60 scientists led by geneticists Eske Willerslev and Morten Rasmussen of the University of Copenhagen.

The original work determining the sequence of DNA in the aboriginal hair was accomplished by Danish and Chinese scientists at their joint genomics center in Shenzhen, China, and was compared with DNA sequences from 79 individuals from Asia, Europe and Africa. The results were then sent to a group at University of California's Berkeley's Center for Theoretical Evolutionary Genomics.

There Rasmus Nielsen and two others in his lab, Yong Wang and Kirk Lohmueller, analyzed and confirmed the DNA sequences, focusing on the DNA obtained from the Aborigine's lock of hair.

Sequencing stretches of DNA in the human genome has long been possible, and scientists can now read the chronological record of human evolution, ethnic relationships and even the history of human epidemics by probing human genes.

"Studying DNA can let you go back for hundreds and hundreds of generations, and, after many complex computer simulations, we have strong statistical evidence that makes us pretty confident that the story of the first major human dispersal is correct," Nielsen said.

The finding is bound to stir up controversy among many anthropologists and archaeologists who have argued that there was only one wave of human migration out of Africa and that it took place over a long period that began some 60,000 years ago.

"The results they provide are pretty substantial, but I wish they had more evidence," said Richard G. Klein, an anthropologist at Stanford who has long studied the movements of early modern humans and who is not part of the Danish-led team.

Scientists generally agree that the aboriginal people of Australia arrived there about 45,000 years ago. In a letter to reporters, Klein said, "I think it's reasonable to suppose that the founding population reached Australia before Eastern and Western Eurasians diverged, and this could imply at least two Out-of-Africa expansions."

But a major problem, he said, is how the first Australians reached the continent across a string of Southeast Asian islands and at least 30 miles of open ocean. There is no archaeological evidence there for boats of any kind, Klein said. Additionally, he added, those first Australians arrived there with only the most crude primitive stone tools similar to those found in Southeast Asia from many millennia earlier. The lock of aboriginal Australian hair that was the key to the study wascollected nearly 100 years ago by an unknown British anthropologist in the southwest Australian mining town of Kalgoorlie. It laid in a succession of Cambridge University museums until Willerslev and his colleagues used it with the permission of the Goldfields Land and Sea Council, the representatives of Kalgoorlie's modern aboriginal population.

(E-mail science writer David Perlman at dperlman@sfchronicle.com.)

(Distributed by Scripps Howard News Service, www.scrippsnews.com.)

 

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