Molar tooth from an ancient human found in Denisova Cave, Siberia

Molar tooth belonging to a Denisovan, thought to be a new branch of ancient humans that overlapped in time with Neanderthals and modern humans. © MPI-EVA, Leipzig

Denisovans, together with Neanderthals, are our closest extinct relatives. They are a recently discovered group of ancient humans from whom only a few fossil fragments, dated to about 40,000 years ago, have been found. 

Not only did this group exist at the same time as modern humans, remarkable genetic research has revealed that they interbred with some populations.

DNA evidence provides clues

In 2010, scientists analysed limited DNA from a fossilised finger and a molar tooth unearthed in Denisova Cave in the Altai Mountains, Siberia. The initial research suggested they were from a genetically distinct group of ancient humans that shared a common ancestor with modern humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) about 1 million years ago. However, the whole Denisovan genome has now been reconstructed and indicates a closer link to the Neanderthals.

Just as remarkable was the discovery that the Denisovans, as this ancient human group has become known, are related to a particular group of humans alive today – Australasians, who live on some of the islands north of Australia and in Australia itself.

Evidence of interbreeding

The study showed that Australasians share around 5% of their genetic material with the Denisovans. The most plausible explanation is that Denisovans were present further south as well as in Siberia, and that they encountered and interbred with pre-Australasian populations of modern humans migrating from Africa though south east Asia around 60,000 years ago.

If the populations were very small, it wouldn’t take much interbreeding to make a genetic mark. As few as 50 Denisovans interbreeding with 1,000 pre-Australasians could result in their present-day descendants sharing 5% of their genetic material with Denisovans.

Human evolution in Asia

Genetic information suggests that Denisovans may have been part of the Homo heidelbergensis lineage. In Europe, Homo heidelbergensis gave rise to Neanderthals, in Africa they gave rise to us (modern humans), and in Asia, perhaps to the Denisovans.