May 10, 2007 — Researchers have produced new
DNA evidence that almost certainly confirms the theory that all modern
humans have a common ancestry. The genetic survey, produced by a
collaborative team led by scholars at Cambridge and Anglia Ruskin
Universities, shows that Australia’s aboriginal population sprang from
the same tiny group of colonists, along with their New Guinean
The research confirms the “Out Of Africa” hypothesis that all modern
humans stem from a single group of Homo sapiens who emigrated from
Africa 2,000 generations ago and spread throughout Eurasia over
thousands of years. These settlers replaced other early humans (such as
Neanderthals), rather than interbreeding with them.
Academics analysed the mitochondrial DNA (mtDNA) and Y chromosome
DNA of Aboriginal Australians and Melanesians from New Guinea. This
data was compared with the various DNA patterns associated with early
humans. The research was an international effort, with researchers from
Tartu in Estonia, Oxford, and Stanford in California all contributing
key data and expertise.
The results showed that both the Aborigines and Melanesians share
the genetic features that have been linked to the exodus of modern
humans from Africa 50,000 years ago.
Until now, one of the main reasons for doubting the “Out Of Africa”
theory was the existence of inconsistent evidence in Australia. The
skeletal and tool remains that have been found there are strikingly
different from those elsewhere on the “coastal expressway” – the route
through South Asia taken by the early settlers.
Some scholars argue that these discrepancies exist either because
the early colonists interbred with the local Homo erectus population,
or because there was a subsequent, secondary migration from Africa.
Both explanations would undermine the theory of a single, common origin
for modern-day humans.
But in the latest research there was no evidence of a genetic
inheritance from Homo erectus, indicating that the settlers did not mix
and that these people therefore share the same direct ancestry as the
other Eurasian peoples.
Geneticist Dr Peter Forster, who led the research, said: “Although
it has been speculated that the populations of Australia and New Guinea
came from the same ancestors, the fossil record differs so
significantly it has been difficult to prove. For the first time, this
evidence gives us a genetic link showing that the Australian Aboriginal
and New Guinean populations are descended directly from the same
specific group of people who emerged from the African migration.”
At the time of the migration, 50,000 years ago, Australia and New
Guinea were joined by a land bridge and the region was also only
separated from the main Eurasian land mass by narrow straits such as
Wallace’s Line in Indonesia. The land bridge was submerged about 8,000
The new study also explains why the fossil and archaeological record
in Australia is so different to that found elsewhere even though the
genetic record shows no evidence of interbreeding with Homo erectus,
and indicates a single Palaeolithic colonisation event.
The DNA patterns of the Australian and Melanesian populations show
that the population evolved in relative isolation. The two groups also
share certain genetic characteristics that are not found beyond
Melanesia. This would suggest that there was very little gene flow into
Australia after the original migration.
Dr Toomas Kivisild, from the Cambridge University Department of
Biological Anthropology, who co-authored the report, said: “The
evidence points to relative isolation after the initial arrival, which
would mean any significant developments in skeletal form and tool use
were not influenced by outside sources.
“There was probably a minor secondary gene flow into Australia while
the land bridge from New Guinea was still open, but once it was
submerged the population was apparently isolated for thousands of
years. The differences in the archaeological record are probably the
result of this, rather than any secondary migration or interbreeding.”
The study is reported in the new issue of Proceedings of the National Academy of Sciences.
Australia’s archaeological record provides several apparent
inconsistencies with the “Out Of Africa” theory. In particular, the
earliest known Australian skeletons, from Lake Mungo, are relatively
slender and gracile in form, whereas younger skeletal finds are much
more robust. This robustness, which remains, for example, in the brow
ridge structure of modern Aborigines, would suggest either
interbreeding between homo sapiens and homo erectus or multiple
migrations into Australia, followed by interbreeding.
The archaeological data also indicates an intensification of the
density and complexity of different stone tools in Australia during the
Holocene period (beginning around 10,000 years BP), in particular the
emergence of backed-blade stone technology. The first dingos arrived at
around the same time, and it is thought both were brought to the
continent by new human arrivals – leading to theories of a secondary
migration that has resulted in disputes regarding the single point of
Source : University Of Cambridge