Professor Alan Cooper, Director of the University of Adelaide's Australian Centre for Ancient DNA (ACAD), and Professor Chris Stringer of the Natural History Museum in the United Kingdom presented new evidence and a new theory that explains why Denisovan DNA only shows up in native peoples in Australia and New Guinea in the Oct. 17, 2013, issue of the journal Science.
The Denisovan gene contribution to man was first discovered in 2010 by a DNA analysis of a finger bone from Denisova cave in the Altai Mountains in northern Asia. Further investigation found Denisovan DNA only in the genes of indigenous populations in Australia, New Guinea, and surrounding areas. No Denisovan DNA can be found in all of Asia.
The researchers propose that early men traveling from Africa to Australia met and interbred with the Denisovan peoples in the islands of Wallacea between Indonesia and Australia.
This conjecture explains how only a few peoples east of Wallace's Line have some Denisovan DNA but no people west of Wallace's Line have any Denisovan DNA. Wallace’s line is a geographic barrier in the ocean just south of Java that was originally defined by the naturalist Alfred Russel Wallace who documented the differences in mammal and bird fauna between the islands either side of the line.
Only people and rodents have ever crossed Wallace’s Line into Australia. The boundary separates the unique marsupial animal population in Australia from the much more varied animal populations in Indonesia and Asia.
Where and when Denisovans met men remains a mystery and why Denisovans did not interbreed with Asian populations closer to their original home is still unknown.