geneticists studying ancient dna discovered a girl whosse parents were two different species

At a laboratory in Leipzig, Germany, postdoctoral researcher Viviane Slon puzzled over a small piece of ancient bone. According to DNA tests, this fragment represented something paleogeneticists never thought they’d find: a hybrid between two of humanity’s early relatives. At first, Slon suspected an error. But the truth soon became apparent—the remains belonged to a girl whose parents were from two entirely different species.

Although scientists have long suspected interbreeding between ancient humans, the chances of finding a first-generation hybrid were considered slim. That changed when researchers in a Siberian cave stumbled upon a tiny bone fragment in 2012. Initially, they didn’t realize it belonged to a hominin—a catch-all term for species regarded as human. For years, the fragment lay in obscurity until Slon, at the Max Planck Institute, extracted its DNA. What she discovered upended decades of research and revealed new truths about early human history.

Ever since Neanderthal remains were identified in Germany in the 1850s, scientists have tried to understand our ancient ancestors. We now know many species walked the Earth before and alongside modern humans. The hybrid discovery—first reported in August 2018—was the first of its kind. Researchers reacted with astonishment.

Modern humans (Homo sapiens) first appeared around 200,000–300,000 years ago. But earlier species, like Australopithecines, emerged more than four million years ago in Africa. These ancestors could walk and climb, though they looked very different from us.

Eventually, species of Homo began to emerge. Their legs became longer, aiding in walking and running, and their brains grew. Around 700,000 years ago, Homo heidelbergensis appeared in Africa and Eurasia. These hominins resembled us more closely and showed advanced tool use and hunting behavior. They may have hunted in groups, suggesting early social structures. Though this species died out, around 390,000 years ago, their descendants gave rise to other species—including modern humans.

Many hominin species likely coexisted and, as scientists now know, interbred. While it’s often claimed that species can’t interbreed, this isn’t a strict rule. For example, horses and donkeys produce mules, which are infertile due to having an odd number of chromosomes. But other species, like gorillas and orangutans, share the same number of chromosomes, making interbreeding more feasible.

There’s evidence of interbreeding among other primates, like bonobos and chimpanzees, and even big cats like lions and tigers (which produce ligers in captivity). Like these animals, early humans also shared chromosome counts and interbred. Homo sapiens are believed to have interbred with Neanderthals after leaving Africa. Today, most people of Asian and European descent have about 2% Neanderthal DNA. We also interbred with another ancient human: the Denisovans.

The Denisovans are a relatively recent discovery. In 2010, researchers at the Max Planck Institute analyzed a tooth and finger bone found in Siberia’s Altai Mountains. They had uncovered a new species. Named after the Denisova Cave, little was known about these early humans—until another bone fragment emerged in 2012.

Originally misclassified with animal bones, the fragment was reevaluated years later by Oxford University’s Samantha Brown. Her analysis revealed it was human. The bone then went to Slon, who analyzed its DNA. It was just one inch long and likely from the leg or arm of a teenage girl who lived about 90,000 years ago.

Slon’s analysis revealed that the girl’s mitochondrial DNA came from a Neanderthal—meaning her mother was Neanderthal. Further study of her nuclear DNA revealed her father was a Denisovan. Even more striking: the genetic material was extremely varied.

This concept, known as heterozygosity, measures genetic variation. If someone’s parents are closely related, heterozygosity is low. But if they come from different species, it skyrockets. Richard E. Green, a computational biologist, said, “It’s heterozygous out the wazoo. That’s really what nails it.”

Slon had found a direct, first-generation offspring of two human species.

“We knew Neanderthals and Denisovans must have occasionally had children together,” Slon told the Evening Standard in 2018. “But I never thought we’d be so lucky to find an actual offspring.”

David Reich, a geneticist at Harvard, agreed. “It seemed unlikely that we’d catch it happening in the act—an individual who’s really a first-generation hybrid.”

The fact that such a discovery was made from a limited sample size raised new questions. If interbreeding were rare, we wouldn’t expect to find direct hybrids among only 23 ancient genomes sequenced up to 2018. Yet researchers had already found two examples: the Denisovan girl (dubbed Denny) and another ancient Homo sapien known as Oase 1.

Oase 1, identified by a jawbone, lived around 37,000 years ago and also carried recent Neanderthal DNA—within four to six generations. That, and the fact that Denny’s Denisovan father also had Neanderthal ancestry, suggests interbreeding wasn’t rare.

According to Svante Pääbo of the Max Planck Institute, “These groups, when they met, mixed quite freely.” Previously, scientists believed these events were rare. Now, that understanding is shifting.

New Theories and Implications

This discovery challenges prior assumptions about ancient human society. Reich told National Geographic, “It qualitatively transforms and changes our understanding of the world.”

Green added that Denisova Cave might have been a hub for ancient interaction—a kind of prehistoric “single bar” for humans of different species.

Katerina Harvati-Papatheodorou from the University of Tübingen suggested survival played a role. “Human groups were very small and vulnerable to drastic mortality,” she said. Cross-species reproduction may have been necessary for survival.

Were Neanderthals and Denisovans wiped out by Homo sapiens? Or were they assimilated? Joshua Akey of Princeton suggested Denny’s DNA points to the latter. As new information surfaces, scientists hope to answer more of these longstanding questions.

For now, one thing is clear: the boundaries between human species were far more flexible than once believed, and one tiny bone fragment has changed the way we see our shared past.