It had been thought that early humans leaving Africa mixed with Neanderthals in the Middle East 50,000 to 60,000 years ago, before migrating to Europe and Asia.

The new evidence shows that early-modern humans, and their sub-species cousins, interbred more recently, during the 5,000 years they co-existed in Eurasia, before Neanderthals became extinct.

The owner of the jawbone from which the DNA was extracted had a Neanderthal in his family tree as recently as four to six generations back, the research shows.

Nine percent of his genome, or genetic code, may have been Neanderthal in origin. The Neanderthal contribution to the genomes of non-African people living today is between 1% and 3%.

Professor Svante Paabo, from the Max Planck Institute for Evolutionary Anthropology, in Germany, said: “It is such a lucky and unexpected thing to get DNA from a person who was so closely related to a Neanderthal. I could hardly believe it, when we first saw the results.”

Neanderthals had been living in Europe for 200,000 years when the first, early-modern humans left Africa to colonise Europe and Asia.

The two groups were different in appearance — Neanderthals were shorter and stockier, with prominent brow ridges — but genetically close for interbreeding.

Neanderthals died out 40,000 years ago. Perhaps they were unable to compete with more sophisticated, modern humans for resources, such as food and shelter. They may also have been ‘assimilated’ through interbreeding.

Archaeological evidence, including changes in tool-making technology, burial rituals and body ornaments, indicates cultural exchange between the two groups when they co-existed in Europe. But because of a lack of skeletons, scientists know little about these people’s physical and genetic make-ups.

The rare jawbone was unearthed from the Pestera cu Oase (“cave with bones”), in the Carpathian Mountains of south-west Romania, in 2002. Radiocarbon dating determined it was between 37,000 and 42,000 years old, and the presence of both X and Y sex chromosomes confirmed it was male.

Results of the genetic analysis appear in the latest online edition of the journal, Nature.

Co-author, Dr David Reich, from Harvard Medical School, in the US, said: “The sample is more closely related to Neanderthals than any other modern human we’ve ever looked at before. We estimate that 6% to 9% of its genome is from Neanderthals. ”