The fossil of a 13-year-old found in Siberia reinforces the theory that different subspecies of human predecessors courted each other and interbred often.
Bengaluru: Ninety thousand years ago, in a remote cave in cold Siberia, a very special baby was born. This little girl was not anatomically human. In fact, neither were her parents. She was born into a tribe of Neanderthals, a sub-human species or a ‘hominin’ that existed until 40,000 years ago.
She died when she was just a little over 13 years old, and buried in the cave in the Altai mountains. A fragment of her bone was discovered by modern homo sapiens in 2012.
It turns out, surprisingly, she was not fully Neanderthal. Her father belonged to another human subspecies called Denisovan. Even though we have seen evidence of the two hominins interbreeding, she is the only known specimen we have who was a first-generation Neanderthal-Denisovan descendant.
Denisova 11, as the newly discovered bone fragment is called, offers compelling clues into our own evolutionary history. “This allowed us to learn about migrations of Neandertals across Eurasia, tens of thousands of years before they disappeared,” said Viviane Slon to ThePrint. Slon is from the Max Planck Institute for Evolutionary Anthropology and is an author of the new study published in the journal Nature.
“These mixed origins allowed us, from a single genome, to gain insights on both the Neandertal population, from which the mother came, and on the Denisovan population, from which the father was,” she added.
The common ancestor of Neanderthals and Denisovans split from the ancestor of modern homo sapiens over 744,000 years ago. Then, about 300,000 years ago, this subspecies moved out of Africa. One branch went north, into Europe and West Asia, eventually becoming Neanderthals. The other branch moved east, becoming Denisovans. Meanwhile, in Africa, 130,000 years ago, modern homo sapiens emerged, ready to spread out into the territories of these subspecies 70,000 years later.
Till a few years ago, we used to think that homo sapiens wiped out other hominins by killing them due to overwhelming numbers. But a new theory that seems to be accepted more today is that sapiens made love, not war.
“The picture that is emerging is that all groups of humans interbred when they met,” says Slon. The study suggests that interbreeding between subspecies is much more common than we thought before.
A lot of evidence lies in our own DNA: today, modern homo sapiens are the only hominin lineage to survive, but we aren’t pure homo sapiens. Our DNA shows that our non-African ancestors have amply interbred with both Neanderthals and Denisovans.
Pacific Islanders living in Papua New Guinea, known as the Melanesians, show evidence of the fact that after homo sapiens crossed the ocean to reach the island, they interbred with Denisovan natives.
Neanderthals vs Denisovans
What we know about Neanderthals is plenty: They were short, stocky, had large noses (for European winters in the Ice Age), and larger bodies than modern humans. They were quite similar to us too. They used fire, tools, sang, tended to the wounded, and drew on cave walls. We know all of this from nearly 500 individual Neanderthal fossils we’ve unearthed over almost two centuries.
However, what we know about Denisovans is far too meagre. We only have four individual Denisovan fossils. And these are not fossils the way we imagine human skeletons; they are just one tooth or one finger per individual. The very first Denisovan fossil we discovered was just 10 years ago, and consisted of one pinkie finger. The finger was crushed for DNA analysis and the findings led to a new hominin being added to our evolutionary textbooks.
It turned out later that two teeth, one discovered in 1984 and the other in 2000 in the same cave, were also Denisovan. Another tooth was discovered in 2010 belonging to a fourth Denisovan. And in 2012, anthropologists found a fragment of a long bone — either arm or leg — of a Denisovan/Neanderthal girl and named it Denisova 11.
So far, all denisovan findings have been from the same cave, the Denisova Cave.
One of the future implications of this study is that we now have more support than ever to hunt for Denisovan fossils in Oceania, the region comprising Melanesia, Micronesia, Polynesia and Australasia. We are not yet certain how far spread out the Denisovans were, but we are getting closer.
“Identifying other places where Denisovans once lived can be done by looking for skeletal remains from relevant archaeological sites and retrieving their DNA,” explained Slon.
Homo sapiens benefitted greatly from interbreeding with other hominins by acquiring improved resilience and immune systems. Neanderthals and Denisovans were well adapted to living in Eurasia before modern humans came along and took from them their red hair and ability to survive in the cold.
Tracing back our lineage help understand the evolution of our own species to a degree greater than before.