Genetics confirms Aboriginal origins

Scientists from Australia and the UK have conducted the first genetic analysis of Australian aborigines to confirm when their earliest ancestors set foot on theAntipodean continent.

Chris Tyler-Smith, from the UK's Sanger Institute where nearly half of the human genome was sequenced a decade ago, working with Melbourne scientist John Mitchell and Aboriginal Elder Lesley Williams, has produced the first complete DNA sequence of the Y chromosomes of 13 male volunteers.

The Y chromosome is carried only by males and passes from father to son. It's useful to study because the other human chromosomes come in pairs, and genetic information can be exchanged between them, blurring the evolutionary time line.

"This lack of mixing keeps the message clearer," says Tyler-Smith.

Comparing the Y chromosome results against data from populations elsewhere around the world shows that the Australian individuals are descended only from ancestors who arrived in the area about 50,000 years ago.

These data, published this week inCurrent Biology, are in agreement with what the archaeological record has established, which indicates that these early arrivals were among the first modern humans to leave Africa, and they populated an ancient continent called Sahul.

This comprised today's Australia, Tasmania and New Guinea and persisted until about 10,000 years ago when rising sea levels reverted the geography to its present form.

Critically, the findings also challenge the claim that a further incursion of migrants came to Australia about 5000 years ago.

At this time, dingoes arrived in Australia for the first time and this coincided with changes in stone tool use, prompting speculation that a fresh wave of human migrants had arrived, possibly from India, at the same time.

The DNA evidence rules this out. "The last time these two populations shared a common ancestor was 50,000 years ago," says Tyler-Smith. "So, once the first ancestors arrived in the area they stayed put, and no one else came in."

Exactly why this first wave of humans were not followed by others is not known.

"These people must have had boats, even then," says Tyler-Smith. "Otherwise they could not have crossed the sea cutting off Papua New Guinea from the rest of Asia. So the lack of a land bridge cannot be the reason. Perhaps the first wave of people prevented others from coming..."