Did Australian Aborigines reach America first?
Thursday, 30 September 2010by Jacqui Hayes
SYDNEY: Cranial features distinctive to Australian Aborigines are present in hundreds of skulls that have been uncovered in Central and South America, some dating back to over 11,000 years ago [9000 BCE or older].
Evolutionary biologist Walter Neves of the University of São Paulo, whose findings are reported in a cover story in the latest issue of Cosmos magazine, has examined these skeletons and recovered others, and argues that there is now a mass of evidence indicating that at least two different populations colonised the Americas.
He and colleagues in the United States, Germany and Chile argue that first population was closely related to the Australian Aborigines and arrived more than 11,000 years ago.
The second population to arrive was of humans of 'Mongoloid' appearance - a cranial morphology distinctive of people of East and North Asian origin - who entered the Americas from Siberia and founded most (if not all) modern Native American populations, he argues.
"The results suggest a clear biological affinity between the early South Americans and the South Pacific population. This association allowed for the conclusion that the Americas were occupied before the spreading of the classical Mongoloid morphology in Asia," Neves says.
Until about a decade ago, the dominant theory in American archaeology circles was that the 'Clovis people' - whose culture is defined by the stone tools they used to kill megafauna such as mammoths - was the first population to arrive in the Americas.
They were thought to have crossed the Bering Strait from Siberia into Alaska at the end of the last Ice Age, some 10,000 or so years ago, following herds of megafauna across a land bridge created as water was locked up in glaciers and ice sheets.
But in the late 1990s, Neves and his colleagues re-examined a female skeleton that had been excavated in the 1970s in an extensive cave system in Central Brazil known as Lapa Vermelha.
The skeleton - along with a treasure trove of other finds - had been first unearthed by a Brazilian-French archaeological team that disbanded shortly after its leader, Annette Laming-Emperare, died suddenly. A dispute between participants kept the find barely examined for more than a decade.
The oldest female skeleton, dubbed Luzia, is between 11,000 and 11,400 years old. The dating is not exact because the material in the bones used for dating - collagen - has long since degraded; hence, only the layers of charcoal or sediment above and below the skeleton could be dated.
"We believe she is the oldest skeleton in the Americas," Neves said.
Luzia has a very projected face; her chin sits out further than her forehead, and she has a long, narrow brain case, measured from the eyes to the back of the skull; as well as a low nose and low orbits, the space where the eyes sit.
These facial features are indicative of what Neves calls the 'generalised cranial morphology' - the morphology of anatomically modern humans, who first migrated out of Africa more than 100,000 years ago, and made it as far as Australia some 50,000 years ago, and Melanesia 40,000 years ago.
New finds in seven sites
When Neves first announced his discovery of Luzia in the late 1990s, he faced criticism from a number of archaeologists, who claimed the dating was not accurate. He has since returned to excavate four other sites, and is still cataloguing skeletons from the most recent dig.
In total, there are now hundreds of skeletons with the cranial morphology similar to Australian Aborigines, found in seven sites - as far north as Florida in the United States to Palli Aike in southern Chile.
In 2005, he published a paper in the U.S journal, Proceedings of the National Academy of Sciences, analysing the characteristics of a further 81 skeletons he recovered from one of four sites, in which he said strengthened his argument that there were migrations to the Americas from at least two major populations.
Not related to Native Americans
In June 2010 in the journal PLoS ONE, Neves and colleagues Mark Hubbe of Chile's Northern Catholic University and Katerina Harvati from Germany's University of Tübingen, showed that it was not possible for the Aborigine-like skeletons to be the direct ancestors of the Native Americans.
Nor was it possible for the two populations to share a last common ancestor at the time of the first entrance into the continent, they argued, based on the 57 cranial measurements that can be made on a skull.
So far, almost all DNA studies of Native Americans points to a single entry from Siberia. This may mean that the original population died out, or simply that DNA studies have been too narrow, argue a number of archaeologists
Genetic evidence needed
"The lack of a perfect match between morphological and molecular information can be easily explained by a very frequent event in molecular evolution: loss of DNA lineages throughout time," Neves says.
"At first, I thought there had been a complete replacement of the population [in South America]," just as there was a replacement of a similar population in East Asia during the Pleistocene/Holocene boundary.
However, he now thinks that the original people were, at least partly, absorbed into the colonising groups. "I have not detected anything that could say they interbred [such as skulls exhibiting mixed cranial features]. "But I think we will. It would be unlikely if these people lived side-by-side for 10,000 years and did not interbreed," he added.
Neves is now calling on molecular archaeologists - experts in the recovery and analysis of DNA - to turn their focus to the question of who Luzia's Aborigine-like people were.