Hamish Clarke
SYDNEY: Aboriginal Australians descend from the same lineage as the first modern humans to migrate from Africa, DNA analysis has confirmed. The find is a further blow to the idea that the evolution of indigenous Australians was marked by many migrations from Asia.
“We wanted to know whether the same ‘Out-of-Africa’ migration that was responsible for founding the gene pools of Eurasia was also the basis for Australia’s population… or were there several separate migrations?” said study co-author and evolutionary biologist Toomas Kivisild, of the University of Cambridge in England.
The Out-of-Africa theory argues that modern humans evolved in Africa 100,000 to 200,000 years ago and one group migrated out to the rest of the world between 50,000 and 70,000 years ago, replacing – and not mixing with – ancient homo populations already there.
Alternative scenarios
Though many anthropologists accepted that Australia’s native population arrived in a single wave 50,000 or so years ago, alternative migration scenarios have been proposed to explain confusing features in the aboriginal fossil record. For example, some experts argue that unusually small and less robust skulls compared to thicker later skulls found among early human remains found in Australia, are inconsistent with an Australian population that had been isolated since its inception.
In order to resolve these questions, lead author Georgi Hudjashov, of the University of Tartu in Estonia, and colleagues compared the DNA of living indigenous Australians in Kalumburu, Western Australia with DNA from people in New Guinea and around the Indian Ocean.
As a kind of belt and braces approach, the team followed both maternal and paternal lineages by analysing mitochondrial DNA (mtDNA) and Y chromosome DNA respectively. MtDNA is used as a record of the maternal line of descent, as it only passes from mothers to daughters in their eggs. Likewise DNA on the Y chromosome is present only in males, so it can be used to trace our paternal lineages.
“Integrating the Y and mtDNA data is a good approach, as usually research teams rely on only the maternal, or paternal, evidence,” commented Peter Brown, a palaeoanthropologist with the University of New England in Armidale, Australia.
Australians evolved in relative isolation compared to other parts of the Indian Ocean.
Little gene flow
Their analysis showed that DNA from people in New Guinea and aboriginal Australians could be traced back to early branches of the human phylogenetic tree, associated with the first humans to leave Africa 50,000 – 70,000 years ago. The study is revealed today in the U.S. journal Proceedings of the National Academy of Sciences.
The DNA analysis also revealed very little gene flow into Australia and New Guinea in the 50,000 or so years since the initial migration. Australians evolved in relative isolation compared to other parts of the Indian Ocean, which were subject to much more genetic mixing, said the study authors. This in turn suggests that developments in language and tool use were not influenced by outside sources, they said.
Not everyone agrees about the proposed extent of differences in Aboriginal fossils anyway. “The variability amongst Australian fossils tends to be exaggerated,” commented David Bulbeck from Australian National University’s School of Archaeology and Anthropology in Canberra. He argues that differences can be explained by climate and it’s effect on physiology, rather than a series of migrations from Asia.
According to palaeoanthropologist Mike Morwood, also of the University of New England in Armidale, the paper confirms what many experts already believed – “that modern humans first appeared in Africa around 200,000 years ago, and that they dispersed out of Africa.”