A set of ancient teeth from China offers a new glimpse into one of the most tangled chapters of human evolution, suggesting that the relationships among early human relatives may have been even more complicated than scientists already believed.
Researchers studying six roughly 400,000-year-old Homo erectus teeth from three archaeological sites in China have identified preserved protein evidence that may point to ancient genetic exchange between populations related to H. erectus and the mysterious Denisovans.
The findings, published in Nature, do not provide a full genome or a definitive answer about how these groups interacted. But they add another thread to the increasingly messy picture of the human family tree, one that looks less like a clean ladder of progress and more like a dense, thorny bramble of overlapping populations.
Modern humans, Homo sapiens, are the only surviving members of the genus today. But for much of the ancient past, Earth was home to several related human groups, including Neanderthals, Homo erectus, Homo habilis, Denisovans, and possibly other still-unidentified populations whose traces survive only indirectly.
Over the last several decades, discoveries from ancient DNA have shown that these groups did not always remain separate. Neanderthals and modern humans interbred. Denisovans contributed DNA to some modern human populations. Neanderthals and Denisovans also mixed with one another. Researchers have even detected genetic signals from unknown “ghost” hominids, suggesting the existence of additional populations whose fossil remains may not yet have been found or identified.
The Denisovans remain especially elusive. Unlike Neanderthals, who are represented by a comparatively rich fossil record, Denisovans are known mostly from fragmentary remains, including teeth, a jawbone, and small pieces of bone. These fossils are distinct from both modern humans and Neanderthals, but there is still not enough evidence to formally classify them with a species name.
Scientists do not yet know whether Denisovans were a single population or a broader collection of related groups. It is also unclear how far they spread across Asia, how long they survived, or when they disappeared. What researchers have been able to determine is that Denisovans were closely related to Neanderthals and shared an ancient common ancestor with both Neanderthals and modern humans.
The new study focuses not on Denisovan fossils directly, but on six Homo erectus teeth excavated from three Chinese sites: Zhoukoudian near Beijing, Hexian in Anhui Province, and Sunjiadong in Henan Province. Homo erectus is an older member of the human lineage and predates modern humans, though it remains part of the broader evolutionary story that eventually led to H. sapiens.
Smithsonian National Museum of Natural History paleoanthropologist Ryan McRae, who was not involved in the study, said the findings help fill in important gaps in scientists’ understanding of human evolution.
“This traces who we are now back to our ancestors in a really cool and exciting way, using new methods.”
Because the teeth are so old, conventional DNA analysis is extremely difficult. Ancient DNA breaks down over time, and after hundreds of thousands of years, it often cannot be recovered under normal preservation conditions. However, teeth offer another route into the past.
Tooth enamel is one of the hardest substances in the body, and it can preserve ancient proteins long after DNA has vanished. Those proteins are produced from genetic instructions, meaning they can sometimes retain clues about inherited DNA variants.
A research team led by paleoanthropologist Qiaomei Fu of the Institute of Vertebrate Paleontology and Paleoanthropology in China extracted and analyzed proteins from the enamel of the six teeth. In all six samples, they found two unusual inherited variants of ameloblastin, a protein involved in enamel formation.
One of those variants appears to be previously unknown. It has not been observed in any other known hominin group, suggesting that the Chinese H. erectus individuals belonged to a distinct East Asian lineage. The second variant is what makes the discovery especially intriguing. That variant had already been identified in Denisovans.
Its presence in all six H. erectus teeth, across multiple sites in China, led the researchers to suggest that the variant may have first emerged in populations related to Homo erectus before later appearing in Denisovans. In other words, rather than the Denisovan-like marker simply showing up by coincidence, the shared protein signature may reflect ancient contact between related populations.
That interaction could have involved interbreeding, though the study does not directly prove it. It does, however, support the idea that ancient human relatives were not isolated groups moving along separate evolutionary tracks. Instead, different populations may have repeatedly overlapped, encountered one another, and exchanged genetic material over long stretches of time.
The fossil record is too thin to say exactly where or when such contact may have occurred. But researchers believe Denisovans and H. erectus may have occupied overlapping parts of East Asia.
“Their shared habitats create opportunities for interactions.”
The findings also suggest Denisovans may have been more genetically diverse than once assumed. If Denisovan populations carried genetic material from groups related to H. erectus, then their history was not simply a split from Neanderthals followed by isolation. It may have included additional contact with older hominin lineages in Asia.
There is also a tantalizing implication for modern humans. Scientists have never recovered a complete Homo erectus genome because available fossils are too old and degraded. But if genetic information from H. erectus-related populations entered Denisovan genomes, and Denisovan DNA later entered modern humans, then some traces of ancient H. erectus-related ancestry could have traveled indirectly into people living today.
The protein variant previously associated with Denisovans was also found in some modern humans, raising the possibility that this inherited marker passed through multiple populations over hundreds of thousands of years.
That does not mean modern humans directly descend from the specific H. erectus individuals represented by the Chinese teeth. The evidence is more cautious than that.
Other recent studies have similarly identified Denisovan ancestry in modern human genomes, particularly in populations with ancestry from parts of Asia and Oceania. Together, these findings continue to show that human evolution was not a simple replacement story in which one group vanished as another appeared.
Instead, the emerging picture is one of repeated encounters, migration, overlap, interbreeding, survival, extinction, and partial genetic inheritance. Some groups disappeared physically, but fragments of their biology may have persisted in later populations.
The new protein evidence from the Chinese teeth does not resolve the larger mystery of who the Denisovans were, how they lived, or exactly how they interacted with other hominins. But it gives researchers another tool for investigating ancient periods where DNA is usually unavailable.
That is especially important for studying Homo erectus, one of the longest-lasting and most geographically widespread human relatives. Since full genomes have not yet been recovered from H. erectus, proteins preserved in tooth enamel may help scientists identify population differences, evolutionary relationships, and possible moments of contact with other groups.
The study’s authors argue that more ancient protein data from different regions and time periods could help clarify how diverse H. erectus populations were and how they may have interacted with Denisovans.
“Further research on H. erectus, including molecular data across different periods and regions, will help to clarify their microevolution, population diversity, and interactions with Denisovans,” the team concludes.
For now, the six teeth offer a small but meaningful clue that the human family tree was never a straight line. It was a web of related groups whose histories crossed, split, merged, and sometimes left only the faintest molecular traces behind.
And as scientific tools become more sensitive, researchers may be getting closer to identifying some of the ancient “ghosts” still hidden in modern genomes.
Moumita Basuroychowdhury is a Contributing Reporter at The National Digest. After earning an economics degree at Cornell University, she moved to NYC to pursue her MFA in creative writing. She enjoys reporting on science, business and culture news. You can reach her at moumita.b@thenationaldigest.com.
