90,000-Year-Old Human Hybrid Uncovered in Ancient Caves

Ninety thousand years ago, a young girl lived briefly in a cave nestled in the Altai mountains of southern Siberia.

Her remains, unearthed by researchers this past summer, are the subject of a study published in Nature.

Homo sapiens are not the only human species to have walked the Earth; until relatively recently, we shared the planet with our evolutionary relatives, the Neanderthals and Denisovans.

It’s believed they disappeared around the same time as the Neanderthals, roughly 40,000 years ago.

The researchers found only a small bone fragment, which, along with the other Denisovan remains, offers limited insight into these ancient people.

The first identification of a Denisovan individual was in 2010 when researchers extracted DNA from a juvenile female finger bone excavated from the Siberian Denisova Cave in the Altai Mountains.

An excavation in the Denisova Cave revealed more fossils belonging to Denisovans. A set of molars indicated that the male Denisovan to whom they belonged inherited 5% of his genome from an ancient, previously unknown population of Neanderthals that inhabited the cave years earlier.

“We aim to find out where they lived, when they came into contact with modern humans—and why they went extinct,” says Katerina Douka of the Max Planck Institute in Jena, Germany, and a visitor at Oxford University.

“It is a wonderful site,” says Tom Higham, deputy director of Oxford University’s Radiocarbon Accelerator Unit and an adviser to Finder.

Scientists have since identified some Denisovan DNA in living humans, including in Papuans and Han Chinese individuals. However, the limited evidence makes it difficult to determine what Denisovans truly looked like.

DNA sequencing of the bone fragment revealed that Denisova 11’s chromosomes were evenly split between Denisovan and Neanderthal origins.

Using ZooMs—a technology that allows collagen, which can survive in bones for hundreds of thousands of years, to be extracted and studied—the team can read structures like a molecular barcode.

However, when the hybrid hypothesis was proposed, the DNA findings provided “good proof that this was real,” as she explained.

Nicknaming her Denny, the team likely discovered the first-generation individual of mixed ancestry. “The DNA of Neanderthals and Denisovans is distinct. We can easily tell them apart. That argues against frequent interbreeding; otherwise, they would have ended up with the same DNA,” the team stated.

Her father’s DNA closely resembled that of the first Denisovan discovered in the same cave, while her mother’s DNA was more similar to Neanderthals who lived in Croatia thousands of years later.

In 2015, scientists discovered the 40,000-year-old remains of a modern human who had a Neanderthal great-great-grandparent.

Although Denisovans and Neanderthals appeared to interbreed repeatedly, their lineages remain distinct. The ancestors of Neanderthals settled in Europe and the Middle East, whereas Denisovans migrated farther east into Asia to evolve separately.

Furthermore, it’s now known that most people outside Sub-Saharan Africa carry some Neanderthal or Denisovan DNA, with the types and amounts varying by region. You, the reader, may even have Neanderthal ancestry!

“It’s truly exciting to have one more genome from this mysterious group,” says population geneticist Priya Moorjani of the University of California, Berkeley.

Since then, evidence of interbreeding between modern humans and other subspecies has steadily accumulated. However, this discovery marks the first direct evidence of interbreeding between Neanderthals and Denisovans themselves.

Both DNA and fossils indicate that modern humans occupied the cave as well, suggesting that Denisovans and Neanderthals in the cave contributed to an intersection of various human types.

The existence of a hybrid individual suggests that interbreeding may have been either common or not particularly unusual, potentially supporting the idea that Neanderthals and Denisovans interbred with humans to the extent that they eventually merged into a single population. More evidence is needed, however, to confirm this theory.

Past studies have provided clear evidence that Denisovans and modern humans interbred at one point, just as modern humans also crossed paths with Neanderthals.

Researchers need to conduct more studies to uncover additional fossils of Denisovans, which could help craft a clearer picture of what ancient humanity looked like.