In 2010, researchers working in the Siberian cave, called Denisova, announced they had found DNA from a scrap of bone representing an unknown group of humans.
Viviane Slon, a paleogeneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who did the ancient DNA analysis, says when she saw the results, her first reaction was disbelief. "But I never thought we would be so lucky as to find an actual offspring of the two groups".
An analysis of the woman's genome, continues Gretchen Vogel in Science, indicates her mother was Neanderthal and her father was Denisovan, the mysterious group of ancient humans discovered in the same Siberian cave in 2011.
Neanderthal, Denisovans, and modern humans all shared a common ancestor more than 400,000 years ago.
Slon extracted mitochondrial DNA, which contains distinct genes passed on by one's mother, from the sample and found that it contained genetic material similar to that seen in Neanderthals.
Tens of thousands of years after Denisova's untimely death, one of her bone fragments has provided the first conclusive evidence of early human interbreeding.
We also know that people from pretty much everywhere but Sub-Sharan Africa have either Neanderthal or Denisovan DNA mixed into their genome; with variations of which and how much varying with geography.
Romeo and Juliet may be history's most enduring pair of star-crossed lovers, but they certainly weren't the first to fall for a purportedly off-limits partner.
"The fragment is part of a long bone, and we can estimate that this individual was at least 13 years old". Although the Denisovans are distinct from Neanderthals and modern humans, researchers know little about their appearance or behavior.
Scientists confirmed Denny came from two separate hominins - and not two hybrids - by looking at where the genomes between Neanderthals and Denisovans differ.
The researchers sequenced the girl's genome from a 2.5-cm-wide bone fragment originally found in 2012 within the Denisova cave-the only place where evidence of Denisovans has been found-of the Altai Mountains in Russian Federation.
They painted animal frescos on cave walls at least 64,000 years ago, well before most Homo sapiens arrived in Europe.
About two percent of DNA in non-Africans across the globe today originate with Neanderthals, earlier studies have shown. 'But when they did, they must have mated frequently - much more so than we previously thought'. The most recent evaluation compared Denny's DNA to genomes of a Denisovan and a Neanderthal.
Until some 40,000 years ago, Europe was home to both groups. They lived in Eurasia, the denisovans in the East, Neanderthals in the West.
It's possible that modern human ancestors killed off the others, but equally possible that a small genetic advantage simply allowed modern humans to outbreed their cousins.