Aborigines, Europeans Share African Roots, DNA Suggests
for National Geographic News
|May 7, 2007|
Where did we come from?
Part of the answer may lie in a new study that suggests Australian Aborigines and Europeans share the same roots—and that both emerged from a wave of African migrations more than 50,000 years ago.
(Related: "Skull Is First Fossil Proof of Human Migration Theory, Study Says" [January 12, 2007].)
Both populations can be traced back to the same founders, according to study co-author Toomas Kivisild of the University of Cambridge.
The finding may strike another nail into the coffin of the "multiregional" hypothesis—the idea humans evolved separately in different parts of the world.
The scientists took blood samples from modern Aborigines and Asian populations and compared their DNA. The researchers then traced the family tree backward through their mitochondrial DNA (the female lineage) and Y chromosome DNA (the male lineage).
(What is human genetics?)
"We could trace back to where the branches join by counting mutations in the DNA," said study co-author Phillip Endicott of the University of Oxford.
Assuming an average DNA mutation rate, the scientists calculated how many years had passed since the populations split.
Boost for "Out of Africa"
All of the Australian lineages fell within four DNA branches, which are associated with the exodus of modern humans from Africa between 50,000 and 70,000 years ago.
As the theory suggests, Africans are believed to have migrated on foot to Eurasia, the large landmass where the European and Asian continents join. The descendants of these migrants may have been able to cross a land bridge between Australia and neighboring New Guinea when sea levels were lower 50,000 years ago (map of the region).
Previously archaeologists have argued that the change in skeletal features seen in Aborigine fossils—from slender about 40,000 years ago to stocky about 13,000 years ago—signals a mixing between modern humans and more ancient populations such as the Neandertals (often spelled "Neanderthals").
But the new DNA results suggest no such intermingling occurred.
"This result provides strong evidence for the 'Out of Africa' hypothesis and gives the multiregionalists much less room to move," said Richard Gillespie, visiting fellow in the Division of Archaeology and Natural History at the Australian National University in Canberra. Gillespie was not involved in the study.
The research will be published in tomorrow's edition of the journal Proceedings of the National Academy of Sciences.
No Outside Influence
The findings may also influence the debate over whether Asian groups migrated to Australia more recently.
Over the last 10,000 years the archaeological record in Australia has changed significantly, including the first appearance of the dingo—a type of dog—and new stone tool industries, "which (may) represent the intrusion of new human migrations into the continent," study co-author Endicott said.
However, the distinctiveness of the Aborigine DNA means the population has remained relatively isolated, ruling out the possibility of later influxes into Australia from Asia.
"If there had been Asian migrations, we would have expected to see regional specific subgroups in the Aboriginal DNA," Kivisild, of Cambridge, said. "But they were completely absent."
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