An analysis of 400,000-year-old tooth enamel has uncovered a genetic link suggesting that Homo erectus interbred with Denisovans hundreds of thousands of years ago, and that the genetic legacy may have reached modern humans through later intermingling with Denisovans, according to a study published Wednesday.
The research, led by Qiaomei Fu of the Institute of Vertebrate Paleontology and Paleoanthropology in China, extracted ancient enamel proteins from six H. erectus teeth — belonging to five men and one woman — recovered across multiple locations in China. Because DNA degrades quickly, the team turned to proteins preserved in tooth enamel, which can survive for millions of years.
All six teeth carried two key mutations in a protein found in enamel, the scientists reported. One mutation has never been observed before and could be a unique calling card of East Asian H. erectus. The second mutation, however, also appears in Denisovans, an extinct human cousin, and in a small fraction of modern humans.
That shared variant suggests that H. erectus could have mated with Denisovans and passed their genes to them. Scientists believe those genes later reached modern humans when our ancestors interbred with Denisovans.
“This traces who we are now back to our ancestors in a really cool and exciting way, using new methods,” said paleoanthropologist Ryan McRae of the Smithsonian National Museum of Natural History, who was not involved with the study.
Homo erectus arose in Africa roughly 2 million years ago and spread across Asia and possibly Europe, with fossil remains found in Indonesia, Spain, China, and Georgia. Yet genetic information about the species has remained elusive because DNA and proteins do not preserve well. The exact relationships between these early human relatives are still unclear; McRae said it is possible that H. erectus is simply an ancestor to the Denisovans, who inherited the genes over time without interbreeding.
The researchers caution that the picture remains incomplete. “We really need to get more DNA” and bits of H. erectus to figure out how this predecessor “is exactly related to other humans,” Fu said. Finding additional fossils and testing the limited evidence for surviving DNA could help firm up the human evolutionary story, the authors said.