Friday, September 23, 2011

Australian Aborigine Hair Tells a Story of Human Migration

Australian Aborigine Hair Tells a Story of Human Migration

The Aboriginal genome bolsters earlier genetic evidence showing that once the Aborigines’ ancestors arrived in Australia, some 50,000 years ago, they somehow kept the whole continent to themselves without admitting any outsiders.

The Aborigines are thus direct descendants of the first modern humans to leave Africa, without any genetic mixture from other races so far as can be seen at present. Their dark skin reflects an African origin and a migration and residence in latitudes near the equator, unlike Europeans and Asians whose ancestors gained the paler skin necessary for living in northern latitudes.

“Aboriginal Australians likely have one of the oldest continuous population histories outside sub-Saharan Africa today,” say the researchers who analyzed the hair, a group led by Eske Willerslev of the Natural History Museum of Denmark.

Dr. Willerslev is an expert at working with ancient DNA, which is usually highly fragmented. Use of the ancient hair reduced the possibility of mixture with European genes and sidestepped the political difficulties of obtaining DNA from living Aborigines.

The DNA in the Aboriginal genome, when compared with DNA from other peoples around the world, shows that when modern humans first migrated out of Africa the ancestors of the Aborigines split away from the main group very early, and before Europeans and East Asians split from each other, Dr. Eske and his colleagues write in an article published online Thursday in the journal Science.

They exclude an alternative possibility, which is that Europeans split first from Asians, and that people from the Asian group colonized Australia.

Based on the rate of mutation in DNA, the geneticists estimate that the Aborigines split from the ancestors of all Eurasians some 70,000 years ago, and that the ancestors of Europeans and East Asians split from each other about 30,000 years ago.

But the genetic data offers no information as to where these populations splits may have occurred, whether in India or even earlier, before the migratory group had left Africa. “We can’t really put the geography in there,” said Morten Rasmussen, a member of the team at the Danish Natural History Museum.
Genetic dates are based on a mixture of statistics and best guesses, but the split times calculated by the Danish team are compatible with the more reliable archaeological dates, which record the earliest known human presence in Australia at 44,000 years ago. The Aborigines’ ancestors could have arrived several thousand years before this date.

The Aborigine occupation of Australia presents a series of puzzles, starting with the nature of their stone tools. The early stone tools found in Australia are much simpler than the Upper Paleolithic tools that appear in Europe at the same era. “I don’t understand why they looked so primitive,” said Richard Klein, a paleoanthropologist at Stanford University.

Primitive as the tools may be, the first inhabitants of Australia must have possessed advanced boat-building technology to cross from the nearest point in Asia to Sahul, the ancient continent that included Australia, New Guinea and Tasmania until the rise of sea level that occurred at the end of the last ice age, 10,000 years ago. But there is no archaeological evidence for boats, Dr. Klein said.

Despite the Aborigines’ genetic isolation, there is evidence of some profound cultural exchange that occurred around 6,000 years ago. The stone tools become more sophisticated, and the population increased. The Aborigines did not domesticate plants or animals, but a wild dog, the dingo, first appears in the
archaeological record at this time. Researchers led by Peter Savolainen of the Royal Institute of Technology in Stockholm reported this month in the journal Proceedings of the Royal Society B that they had traced the spread of the dingo across the islands of the Pacific by analyzing ancient DNA in the bones of Polynesian dogs.

The dingo originated on the Asian mainland and became part of the Polynesian domestic menagerie along with the pig, the chicken and the rat. This ensemble had reached New Zealand by A.D. 1250. How the dingo arrived in Australia is an “enigma,” Dr. Savolainen writes, because none of the other elements of Polynesian culture are found there.

Even stranger, dogs always travel with their masters, yet there is no sign yet of Polynesian genes in the Aborigine population.

Most of Australia is a forbidding desert, and this barrier may have been the downfall of most invasions, whether of people or of animals, Dr. Klein said. The ancestors of the Aborigines were lucky enough to find their way south, where there is more vegetation, and the dingo is a skillful hunter, able to look after itself. But this leaves unexplained the cultural changes that began around or shortly after the dingo’s arrival.

“Something remarkable happened in Australia 6,000 to 4,000 years ago, and it involved much more than the dingo,” Dr. Klein said.


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