Experts are now convinced that early modern humans and Neanderthals interbred between 50,000 and 100,000 years ago.

As a result, between one and four per cent of our DNA comes from the prehistoric creature, according to the research.

Human-Neanderthal relations occurred as the first pioneering bands of homo sapiens ventured out of Africa, scientists believe.

When they reached the Middle East they ran into groups of Neanderthals who preceded them and it is now thought that they mated.

The discovery emerged from the first attempt to map the complete Neanderthal genetic code, or genome. It more or less settles a long-standing academic debate over interbreeding between separate branches of the human family tree.

• Evidence in the past has pointed both ways, for and against modern humans and Neanderthals mixing their genes.

Technically the Neanderthals, homo neanderthalensis, were a human subspecies which parted evolutionary company from our direct ancestors between 270,000 and 440,000 years ago.

Around 400,000 years ago early Neanderthals stepped out of their African cradle, where Homo sapiens was still evolving, and headed for Europe and Asia.

At least 300,000 years later early modern humans followed the Neanderthals out of Africa.

The two populations coexisted in Europe and Asia until the Neanderthals vanished forever around 30,000 years ago – probably driven into extinction by the smarter and more competitive modern humans.

Professor Svante Paabo, director of evolutionary genetics at the Max Planck Institute in Leipzig, Germany, who led the international project, said that humans in Europe all have “caveman biology”.

African humans did not come into contact with Neanderthals but may have bred with other unknown human sub species, he said.

The research, which took four years and is published in the journal Science, involved disentangling and making sense of 1.1 billion DNA fragments taken from Neanderthal bones.

Young Neanderthals’ teeth growth was significantly faster than in our own species Photo: HULTON ARCHIVE