Interbreeding and incest common among early humans, says study

A tiny toebone from a Neanderthal woman who lived around 50,000 years ago has shown that several branches of early humans interbred before a single group, Homo sapiens, rose to dominate.

The bone has provided the final piece to a project, launched in 2006 by European evolutionary anthropologist Svante Paabo, to use ancient DNA to trace the human odyssey.

In a study published in the journal Nature on Wednesday, a team reports that the bone adds hugely to genetic knowledge of our cousins, the Neanderthals, who died out around 30,000 years ago.

The scientists compared the genome against those of two other human groups who shared the planet at the same time.

They were the Denisovans, another mysterious sub-group whose remains have been found in Siberia; and Homo sapiens, as modern man is called.

The comparison points to interbreeding - "gene flow" in scientific parlance - among the three groups, although the extent is rather limited.

Between 1.5 and 2.1 per cent of the genomes of humans today can be attributed to Neanderthals, it found. The exceptions are Africans, who do not have a Neanderthal contribution.