A team of scientists has announced remains of a human girl from about 50 thousand years ago had one Neanderthal parent and one Denisovan parent, two different species of humans, both species now extinct. The results, from genomic tests in Leipzig, Germany of fossil bone from Siberia, Russia, were published on Wednesday in scientific journal Nature. The researchers said this is the first discovery of a child with parents of different human species.
The single fossilized bone fragment, about two centimetres (less than an inch) long, which researchers said was from a girl at least 13 years old, was found in 2012 in the Denisova Cave in Siberia. The Denisovan species of humans is only directly known from the same cave, where it was discovered in 2011; the cave is also the only site where both Nenderthal and Denisovan remains have been found. Neanderthals have been found in Europe and Asia. Traces of genes from both species occur in some modern humans. Researchers found the nuclear DNA in this bone fragment was split fairly evenly between both species, while the mitochondrial DNA was Neanderthal; nuclear DNA comes from both parents, while mitochondrial DNA comes only from the mother, so they concluded the girl's mother was Neanderthal and her father Denisovan.
Lead author on the study Viviane Slon, of the Max Planck Institute for Evolutionary Anthropology (MPI-EVA) in Leipzig, said:
We knew from previous studies that Neanderthals and Denisovans must have occasionally had children together [...] But I never thought we would be so lucky as to find an actual offspring of the two groups.
The team rechecked the findings several times. Scientist Johannes Krause, of the Max Planck Institute for the Science of Human History in Jena, called the finding "sensational". Study coauthor Svante Pääbo, of MPI-EVA, remarked on the improbability of discovering such a hybrid when only two dozen human genomes over 40 thousand years old — when the other species of humans were still around — have been done:
The fact that we stumbled across this makes you wonder if the mixing wasn't quite frequent [...] Had it happened frequently, we would not have such divergence between the Denisovans and Neanderthal genomes.
The researchers also noted the girl's father, though Denisovan, had a trace of Neanderthal DNA, from perhaps as much as several hundred generations earlier. They also reported the mother's DNA was not closely related to that of other Neanderthals found in the cave, suggesting multiple migrations of Neanderthals between Siberia and Europe.