Ancient teeth reveal Homo erectus interbred with human ancestors 400,000 years ago

Six teeth pulled from archaeological sites across China are rewriting what we know about human ancestry. The teeth, roughly 400,000 years old, belonged to five men and one woman of Homo erectus—a species that emerged in Africa around two million years ago and eventually spread across Asia, Europe, and beyond. What makes these particular teeth remarkable is not their age or their geography, but what scientists found locked inside their enamel.

Researchers extracted ancient proteins from the tooth enamel and analyzed them for genetic mutations. They found two significant variants. The first was entirely new to science—a mutation that appears to be a distinctive marker of Homo erectus populations in East Asia, never before documented in any other species or population. The second mutation told a more complicated story. This variant showed up not only in these ancient teeth but also in a small subset of modern humans alive today. It also appeared in Denisovans, an extinct human relative known mainly from fragmentary fossil evidence and genetic traces.

The presence of that shared mutation opened a window onto an ancient encounter. If Homo erectus and Denisovans both carried the same genetic variant, the most straightforward explanation is that they interbred at some point in the deep past. Genes passed from one species to the other. But the chain of inheritance did not stop there. Denisovans, in turn, later interbred with the direct ancestors of modern humans—a process documented in previous genetic studies. That means the genetic signature found in these Chinese teeth, passed through Denisovans, eventually reached us.

The discovery is significant because it uses a new method to trace human evolutionary history. Rather than relying solely on DNA—which degrades rapidly and is rarely recoverable from specimens this old—the researchers worked with proteins in tooth enamel, which are far more stable over geological timescales. This approach allowed them to extract biological information from fossils that would otherwise yield nothing. "This traces who we are now back to our ancestors in a really cool and exciting way, using new methods," said Ryan McRae, a paleoanthropologist at the Smithsonian National Museum of Natural History who was not involved in the research.

Yet the picture remains incomplete. Scientists still cannot say with certainty exactly how Homo erectus relates to Denisovans and to us. One possibility is that Homo erectus was a direct ancestor of Denisovans, who simply inherited these genes over time rather than acquiring them through interbreeding. Another scenario involves more complex interactions between multiple populations. The genetic evidence points toward contact and gene flow, but the exact architecture of these ancient relationships remains unclear. "It's a tough puzzle to detangle with extremely limited data," McRae acknowledged.

Qiaomei Fu, the study's lead author from the Institute of Vertebrate Paleontology and Paleoanthropology in China, emphasized the constraints researchers face. "We really need to get more DNA and bits of H. erectus to figure out how this predecessor is exactly related to other humans." Finding additional fossils, extracting more protein and DNA evidence, and testing these materials with increasingly refined methods will be essential to clarifying the evolutionary story. For now, these six teeth from China have opened a door into a moment when our ancestors walked the earth alongside other human species, and genes moved between them in ways that shaped the biology of everyone alive today.