Wednesday, 28 September 2011

Genetic Evidence Suggests That Asia Was Settled By Humans In Multiple Waves

To extract DNA from fossil bones, scientists use
dentists drills to remove analysable material. 
Genetic evidence is fast becoming part of the everyday scientific world, including the study of palaeontology. We can study mitochondrial mutations and DNA maps to peer deeper and deeper into the past. Now scientists from the Harvard Medical School and the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have used this remarkable new science to study how Asia was first settled by modern humans by studying genetic patterns, obtained from state of the art genomic analysis.

Their research shows that Asia was settled in multiple waves of migration. This is contrary to all other genetic studies which suggests colonisation by around 65,000 years ago. According to David Reich, genetics professor at Harvard, the recently discovered species of humans given the generic name of the Denisovans, migrated into Asia and interbred with the modern human populations leaving a genetic heritage that shows traces even today, tens of thousands of years later.

Using the genetic information recently extracted from the finger bone of the Denisovan first known to science, the team compared their genome to ours and discovered some surprising facts. Denisovan DNA is very distinctive and leaves a trail through its descendants. It can be recognised in even tiny sections of the genome. Reich's work builds on earlier research into the first ever population analysis of the Denisovans.

The trail shows that the strange new species of human lived, not only in Russia and Siberia, but actually had a far reaching geographical range into South East Asia and Oceania, interbreeding with the native human populations, adding to the genetic range in the Papua New Guineans and the Aborigines as well as mainland Asia. The team concluded that the Denisovans interbred with modern humans in South East Asia around 44,000 years ago before the divergence of the Papua New Guineans and the Aborigines.

They also concluded that South East Asia was first colonised by anatomically modern humans unrelated to present day Chinese and Indonesians. It had been previously suggested that the modern populations of Oceania are descended from members of our species which followed a southern, coastal route through India, China and Burma while archaic populations came from the north (the Denisovans came from northern Russia and Siberia). However there was little genetic evidence previously to support this.

It also adds to the bank of growing evidence that the Denisovans are not descended from modern humans or Neanderthals, but share a common ancestor. Mark Stoneking, a professor at the Max Planck Institute who is senior author of the paper, stated that 'the fact that Denisovan DNA is present in some aboriginal populations of South East Asia but not in others shows that there was a checkerboard of populations with and without Denisova material more than 44,000 years ago. The presence of Denisovan genetic material in some but not all the groups can most easily be explained if Denisovans lived in South East Asia itself.'