It is well-known today that some of the ancestors of modern humans interbred with Neanderthals, a closely-related human species or sub-species that lived 130,000 to 30,000 years ago in Eurasia. Less known is a new study by researchers at Uppsala University, indicating that the modern human ancestors of East Asians interbred with archaic humans known as Denisovans about 20,000 years ago.
     The existence of Denisovans came to light in March 2010 when it was announced that a finger bone fragment of a juvenile that lived about 41,000 years ago had been discovered in Denisova Cave (Altai Krai, Russia), an area inhabited at the same time by modern humans and Neanderthals. The discovery of a tooth and toe bone from two other individuals of the same population added to the evidence. Based on analysis of mitochondrial DNA, researchers determined that the bone finds belonged to a new species of humans.
     Mattias Jakobsson, who conducted the new study along with Pontus Skoglund, says, "Hybridisation took place at several points in evolution, and the genetic traces of this can be found in several places in the world. We'll probably be uncovering more events like these."
     Previous studies indicated the occurrence of two separate hybridisation points between archaic humans, who are genetically and morphologically different from modern humans, and modern human ancestors after leaving Africa. One occurred between Neanderthals and modern humans, and the other between Denisovans and ancestors of Oceanians, but the latest study indicates that hybridisation also occurred in East Asia.
     "We found that individuals from mainly Southeast Asia have a higher proportion of Denisova-related genetic variants than people from other parts of the world," says Jakobsson. But, adds co-researcher Pontus Skoglund, "we still know very little about the history of these groups and when their contacts with modern humans occurred."

Edited from Popular Archaeology (31 October 2011), The Telegraph (1 November 2011)