Human evolution’s biggest mystery has started to unravel. How 2025 tipped the scales

The greatest mystery in human evolution, which emerged 15 years ago from a 60,000-year-old pinky bone, finally began to be solved in 2025.

Analysis of DNA extracted from the fossil electrified the scientific community in 2010, when it revealed a previously unknown human population that had, in the distant past, encountered and interbred with our own species, Homo sapiens. This enigmatic group became known as the Denisovans, after the Denisova Cave in the Altai Mountains of Siberia, where the little finger was discovered.

Despite extensive knowledge of the genetic makeup of this population, traces of which are traced to millions of people today, scientists knew nothing about what the Denisovans looked like, where they lived, or why they disappeared. The discovery and the questions it raised galvanized an entire generation of geneticists, archaeologists and paleoanthropologists.

Some of that work paid off this year, and scientists finally put a face to the Denisovan name by extracting new clues from another well-known fossil: a prehistoric human skull that didn’t seem to fit any known group. Today, other pieces of the puzzle have started to fall into place.

Enter “Dragon Man”

When the skull was discovered in Harbin, northeast China, in 2018, after being hidden at the bottom of a well for decades, some scientists had a hunch it might be Denisovan.

DNA sequences from the group had been detected in the genomes of modern-day Asians, but not Europeans, suggesting that this region was where Denisovans primarily lived.

Based on its distinctive shape, researchers assigned the skull to a new species they called Homo longi or “Dragon Man.” The dozen Denisovan fossils identified since 2010 using DNA were too small and fragmentary to warrant an official species name.

Obtaining ancient DNA from the skull, estimated to be 146,000 years old, was key to understanding whether there was a connection between Dragon Man and the Denisovans. However, this proved tricky.

A team led by Qiaomei Fu, a geneticist and professor at the Institute of Vertebrate Paleontology and Paleoanthropology, part of the Chinese Academy of Sciences in Beijing, tested six bone samples from Dragon Man’s only surviving tooth and the petrous bone of the skull, a dense piece at the base of the skull that is often a rich source of DNA in fossils. However, the samples yielded no results.

But Fu, who as a young researcher was part of the team at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, that first discovered Denisovans, reported in June that her team was able to recover Denisovan genetic material from an unexpected source: Dragon Man’s dental calculus — the gunk left on teeth that can, over time, form a hard coating and preserve the mouth’s DNA.

This information was not an obvious result. The genetic material the researchers had recovered was mitochondrial DNA, which, unlike nuclear DNA, is only inherited through the maternal line, providing an incomplete picture of an individual’s genomic ancestry. This discovery potentially meant that Dragon Man could have been a mix of two species, which is not unprecedented. In 2018, scientists discovered a fossilized bone from Denisova Cave that belonged to a girl whose mother was Neanderthal and father Denisovan.

However, the team also recovered protein fragments from the petrous bone samples, which, although less detailed than DNA, suggested that Dragon Man’s skull belonged to a Denisovan population.

Together, the two pieces of evidence “have cleared up some of the mystery surrounding this population,” Fu told CNN in June when the research was published. “After 15 years, we know the first Denisovan skull.”

The DNA discovery makes it likely that Homo longi will become the official designation for a dozen other Denisov fossils, Chris Stringer, a paleoanthropologist and head of human evolution research at the Natural History Museum in London, said in an email.

Ryan McRae and Briana Pobiner, paleoanthropologists at the Smithsonian National Museum of Natural History, agreed, although they said the name Denisovan would likely persist as a popular name, much like how most people call Homo neanderthalensis Neanderthals today.

“Although more work remains to be done to bring together the full body of evidence and give scientists a more complete view of Denisovan anatomy, habitat, and behavior, being able to connect complete fossils with molecular evidence is a huge step forward,” McRae and Pobiner wrote in an annual list of the top stories of human evolution.

Additional evidence may be available, waiting to be identified, the researchers suggest, and with it, 2026 could be set for more groundbreaking revelations.

A portrait of a Denisovan

A fossil skull, with its telltale bumps and ridges, can reveal a lot about an individual’s appearance, according to John Gurche, a paleoartist who creates reconstructions of ancient human ancestors for museums including the Smithsonian and the American Museum of Natural History. He recreated Dragon Man’s face for National Geographic.

Assuming that Dragon Man’s skull belonged to a typical Denisovan individual, scientists said the ancient human would have had pronounced brow ridges, large teeth and lacked a high forehead. But if he were dressed in modern clothes, this prehistoric relative might not have attracted too many stares on a subway train.

Gurche said he used the known relationships between soft and bony tissues in humans and monkeys to recreate facial features, such as the width of the eyeball, the dimensions of the nasal cartilage and the thickness of the soft tissues in certain parts of the face. Features about which the skull “offers little information,” including the shape of lips and ears and the location of hair, were more difficult to understand.

With molecular evidence now linking Dragon Man to the Denisovans, it will be easier for paleoanthropologists to identify other potential Denisovan remains, including skull fossils from sites in China that have long defied classification.

Further revelations may come from another fossil skull discovered in China in 2022, which has not been formally described in the scientific literature. It is the third skull discovered at the site known as Yunxian, in China’s Hubei province, and is thought to date back around 1 million years. The other two skulls were discovered in 1990.

A digital reconstruction published in September of the second, badly crushed skull from the site suggested it was an early ancestor of Dragon Man, meaning the lineage may have originated much earlier than previously thought.

The researchers’ broader analysis, based on the reconstruction and more than 100 other skull fossils, also significantly pushes back the timeline for the emergence of species like our own, Homo sapiens and Homo neanderthalensis, by 400,000 years.

However, the results were met with some skepticism. More details about the third Yunxian skull would allow the team to test the accuracy of the reconstruction and its placement in the human family tree.

Oldest genome poses new questions

A 200,000-year-old tooth, similar in appearance to the molar still attached to Dragon Man’s skull, could well shake up what is known about Denisovans and the human family tree more broadly next year and beyond. Researchers found the tooth during an excavation of Denisova Cave in 2020.

Stéphane Peyrégne, a researcher at the Max Planck Institute for Evolutionary Anthropology, and his colleagues have since analyzed the molar and recovered the complete genome of a Denisovan – a set of highly detailed genetic information that can reveal past genetic diversity and evolution.

This is only the second time that scientists have successfully sequenced a “high coverage” genome from a Denisovan fossil – the first was from the finger fossil that revealed the existence of Denisovans.

The scientists shared the genome analysis in October on what’s called a preprint server, which allows study authors to post early versions of their work online and is being reviewed by other researchers. Peyregne declined to comment on the document until it is officially released next year. Stringer called the results “very important.”

The genome allows for further research into Denisovan’s biological traits that could influence human health today. For example, a study published in August suggested that a variant of the Denisovan gene involved in mucus and saliva production could have helped Homo sapiens adapt to new environments.

The new genome is also much older than the first and allows geneticists to delve deeper into the history of Denisovan and reconstruct the relationships between different ancient populations.

The genome represents a Denisova man who lived in a small group 200,000 years ago in the Denisova Cave. Analysis of the group revealed that not only had its ancestors apparently interbred with early Neanderthals, but the individual also had ancestors from an unknown “super archaic” group for which no ancient DNA matches currently exist.

McRae of the Smithsonian said that traces of these “ghost lineages” have also been found in the DNA of modern humans, and that scientists are not sure of their identity. They could represent other extinct hominids such as Homo erectus or Homo floresiensis, sometimes known as the “hobbit”.

“Or, it could represent hominids that we really haven’t found in the fossil record. They’re ghosts until we have something to trace them back to,” he said by email.

Determining the identity of this group will be a new mystery for human evolution experts to ponder in 2026.

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