A new character in the story of our evolution
Scientists identify the first known offspring of Neanderthal and the mysterious Denisova
From fragments of DNA in a 50,000year-old finger bone, scientists have identified a fascinating new character in the story of our evolution: the firstknown offspring of parents from two different branches of the human family tree.
The bone belonged to a 13-year-old girl whose mother was a Neanderthal — one of the ancient people who inhabited Europe and Asia between 450,000 and 40,000 years ago. But the girl’s father was a Denisovan — a mysterious offshoot of the genus Homo known only from a few bits of bone and the faint signatures that still linger in the genomes of modern humans.
The report Wednesday in the journal Nature adds to a growing body of evidence that ancient hominids — including some of our own direct ancestors — interacted and interbred repeatedly over the course of evolutionary history.
Modern genetic analyses suggest that people of European and Asian ancestry have roughly 2 per cent Neanderthal DNA, and some East Asians and Pacific Islanders can trace as much as 6 per cent of their genetic material to the Denisovans. The intermingling was pervasive enough that some scientists question whether our extinct cousins should be considered a subpopulation of Homo sapiens, rather than a distinct species, as they are typically defined today.
But in those studies, any prehistoric hanky-panky seemed like an abstraction — something done by unknown people untold millennia ago.
“The cool thing about this is, this is extremely direct evidence,” said Svante Paabo, a molecular geneticist at the Max Planck Institute for Evolutionary Anthropology in Germany who led the new research. “We’ve almost caught them in the act, so to speak.”
Eight years ago, Paabo was part of the team of scientists who sequenced DNA from bits of human bone found on the floor of a remote cavern in the mountains of Siberia. The mitochondrial DNA — a type of genetic material passed down from a person’s mother — was unrecognizable.
“Whoever carried this DNA out of Africa is some new creature that hasn’t been on our radar screen so far,” his colleague Johannes Krause told The Washington Post at the time.
Krause, Paabo and their colleagues named the new hominid after Denisova Cave, where the 40,000-year-old remains were found. Subsequent studies allowed researchers to piece together the person’s nuclear DNA — the paired chromosomes inherited from both parents, which are stored in the nucleus of every cell. They also uncovered remains of additional Denisovan individuals, as well as those of a Neanderthal woman who lived in the cave tens of thousands of years earlier.
It turns out that Denisovans were a distinct lineage of protohuman that split off from Neanderthals about 400,000 years ago. Both groups shared a common ancestor who migrated out of Africa a few hundred thousand years before that. Their group split off lineage that led to Homo sapiens sometime in the past million years.
As a result, scientists like to compare the planet during that period to J.R.R. Tolkien’s Middle Earth — except instead of hobbits, dwarves and elves, there were different kinds of humans.
Denisovans have been found only in that single cave. But Neanderthal fossils show they flourished in Eurasia, ranging from the British Isles to Siberia until, about 40,000 years ago, they abruptly vanished from the face of the Earth. Around the same time, the Eurasian population of a new primate — Homo sapiens — began to explode.
“Something happened that only we survived,” Paabo speculated in 2010. He proposed a few possible narratives, all of them grim: Maybe modern humans outcompeted our cousins for precious resources. Or maybe we just killed them.
But “Denisova 11” — the owner of the genome sequence reported Wednesday — highlights a more romantic, more complex and increasingly compelling story.
“This paper and other papers are showing the model of having isolated populations is not quite accurate,” said Emilia Huerta-Sanchez, a population geneticist at Brown University.