Monday, May 07, 2007

Genetic tests on Australian fossils suggest Aborigines did migrate out of Africa

From
May 8, 2007

Genetic tests on Australian fossils suggest Aborigines did migrate out of Africa

Australia – along with the rest of the world – was first settled by a single group of settlers who left Africa more than 55,000 years ago, DNA research suggests.

Once there, they apparently evolved in relative isolation, developing genetic characteristics and technology found nowhere else until the arrival of the first European settlers.

The uniqueness of Australia’s ancient Aborigines and archaeological finds on the continent have previously threatened to undermine the “out of Africa” hypothesis of human origins favoured by most experts.

But the latest research by geneticists at the University of Cambridge reinforces the theory that all modern human beings belonging to the species Homo sapiens are descended from a small number of Africans who left their home between 55,000 and 60,000 years ago.

According to the fossil record, Homo sapiens emerged as a new species about 120,000 years ago in central East Africa.

It is thought to have migrated from there into the Middle East, southern Africa, Europe, central Asia, and the New World, replacing older human species such as Neanderthals and Homo erectus in the process.

Critics of this theory say that modern human beings may have evolved in a number of different places, arisen through interbreeding, or made several trips out of Africa.

Their main evidence comes from Australia, where skeletal and tool remains are strikingly different from those on the “coastal expressway” route the early settlers are supposed to have taken through south Asia.

Some anthropologists have argued that this is evidence against the idea of a single common origin for modern-day humans.

But a study of DNA samples from Aboriginal Australians and Melanesians from New Guinea appears to verify the single migration theory.

Both populations were found to share genetic features linking them and other Eurasians to the exodus from Africa more than five millennia earlier.

Their ancestors would have travelled to Australia via Arabia, Asia and the Malay peninsula, dispersing at a rate of about one kilometre a year, according to Peter Forster, who led the Cambridge research, which is reported today in the journal Proceedings of the National Academy of Sciences.

Dr Forster, who is now at Anglia Ruskin University, said yesterday: “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.”

The scientists found no evidence of any interbreeding with Homo erectus, Australia’s original inhabitants.

The timing of Ice Age coolings, and the amount that they lowered ocean levels, specifies the geological periods in which it was possible to migrate to land masses otherwise separated by water.

Fifty thousand years ago Australia and New Guinea were joined by a land bridge, which became submerged 8,000 years ago. Early settlers could have reached New Guinea across narrow straits, which were all that separated the region from the main Eurasian land mass.

The DNA patterns suggest that there was little gene flow into the region after the migration. That Australian and Melanesian populations evolved on their own explains why some of their shared features are so unusual, the scientists say.

Toomas Kivisild, from the Department of Biological Anthropology at the University of Cambridge, who co-authored the paper, 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.”

The origins of Man

— In 1924 Raymond Dart discovered a specimen later known as Taung Child, an australopithecine infant discovered at Taung, South Africa. Various traits convinced Dart that the baby was a bipedal human ancestor, a transitional form between apes and humans

— Lucy, a 1.1m-tall adult skeleton of a human ancestor, or hominid, that lived up to 3.6 million years ago, was discovered in Hadar, Ethiopia, in the 1970s

— “Millennium Man”, or Orrorin, was unearthed in Kenya last year by scientists who claimed he was Man’s earliest known relative

Source: Times database

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