Genetics Suggest Early Human Ancestors Crossed Marine Barrier and Mated With Modern Humans

A team of scientists claims that the recently discovered ancient human relatives 'the Denisovans', crossed the marine barrier in Indonesia and mated with modern humans.

Genetic analysis suggests that Denisovans, the ancient human species that coexisted with Neanderthals and modern humans, successfully crossed the Wallace's line, one of the world's prominent marine barriers in Indonesia and later interbred with modern humans moving through the area on the way to Australia and New Guinea.

Researchers unearthed a small fragment of a finger bone in a Denisova cave on Altai Mountains of Asia in 2010. The genetic analysis of the finger bone led to the complete genome sequence of a new line of human family tree,  the Denisovans, and the presence of their DNA was detected in native populations of Australia, New Guinea and regions around it. On the other hand, the Denisovan DNA appears to be absent in mainland Asia population despite the fossil being discovered in Asia.

Now researcher Alan Cooper of the University of Adelaide in Australia and Chris Stringer of the Natural History Museum in the U.K. suggest that the this DNA pattern could happen only if the Denisovans were successful in crossing the marine barrier of the famous Wallace's Lines, one of the world's biggest biogeographic barriers that is formed by marine current along the east coast of Borneo. Wallace Line marks the division of the European and Asian mammals.

"In mainland Asia, neither ancient human specimens, nor geographically isolated modern indigenous populations have Denisovan DNA of any note, indicating that there has never been a genetic signal of Denisovan interbreeding in the area," Professor Cooper, Director of the University of Adelaide's Australian Centre for Ancient DNA, said in a statement. "The only place where such a genetic signal exists appears to be in areas east of Wallace's Line and that is where we think interbreeding took place - even though it means that the Denisovans must have somehow made that marine crossing."

Data suggests that male Denisovans interbred with modern human females, indicating that a small number of modern humans initially crossed the Wallace's Line and barged into the Denisovan territory.

Another recent discovery of the ancient human species Homo Floresiensis (hobbits), in Flores, Indonesia, confirmed that there were more human ancestors in the area than previously believed. Hobbits being different from Denisovans highlight that there were more unexpected groups in the area.

"The conclusions we've drawn are very important for our knowledge of early human evolution and culture. Knowing that the Denisovans spread beyond this significant sea barrier opens up all sorts of questions about the behaviours and capabilities of this group, and how far they could have spread," Professor Cooper explains.

Next, the team plans to solve the mystery regarding when and where the ancestors of the current humans, who were on their way to colonize New Guinea and Australia around 50,000 years ago, encountered the Denisovans.