Furthermore, the fossil had Neanderthal mitochondrial DNA. This is passed from mother to child,
which meant that either the teenager was the daughter of a Denisovan father and a Neanderthal mother
or had come from a population with an extensive mix of traits, and had been born to parents who were, in effect, hybrids.
Biologists know that animal populations of mixed ancestry
who are undergoing little evolutionary change show signs of this equilibrium in their genes.
Drs Slon and Paabo looked for just such markers in the genes of their Denisovan teenager and found none.
That ruled out the idea that she came from mixed ancestry.
They did, though, find that each chromosome pair the girl carried had one chromosome that was entirely Neanderthal in origin
and one that was almost entirely Denisovan. This signified that she had one parent from each group.
Knowing that the mother was a Neanderthal from the girl's mitochondrial DNA, means that her father must have been a Denisovan.
The 2013 analysis of the Denisovan fossil also showed interbreeding, albeit of a more distant sort.
Add in this latest research, and although Neanderthals and Denisovans may not have met very often,
sex between them is likely to have been more common than was previously realised.
The implication is that modern humans are likely to have a messier genetic heritage than once thought.