Ancient teeth, preserved enough to hold chemical traces, are giving scientists a rare window into interactions among early human relatives and how those interactions may have shaped what people carry today. The new study focused on Homo erectus, a lineage that arose in Africa about 2 million years ago and then spread across parts of the globe, including Asia and possibly Europe.
Because genes and proteins generally do not preserve well in fossil remains, researchers said information about what internal makeup looked like in these early populations has been difficult to obtain. In the new work, the researchers instead siphoned ancient enamel proteins from H. erectus teeth belonging to five men and one woman recovered across several locations in China.
The teeth examined were about 400,000 years old, and the analysis looked for mutations in a protein found in tooth enamel. The researchers reported two key mutations. One mutation had not been observed before, and the researchers suggested it could represent a unique calling card linked to East Asian members of H. erectus.
The second mutation was more complex, the study said, because the scientists identified a variant that also appears in a small fraction of modern humans and in one of the extinct cousins known as Denisovans. Interpreting that pattern, the researchers said the Denisovan-related variant could have entered the Denisovan lineage in the past through H. erectus mating, and that subsequent contact between the groups could help explain how the genetic signal later reached modern people.
A paleoanthropologist not involved in the research, Ryan McRae of the Smithsonian National Museum of Natural History, described the work as an advance in methods. “This traces who we are now back to our ancestors in a really cool and exciting way, using new methods,” McRae said, in comments included in the report.
McRae also said the broader evolutionary relationships among these early human groups remain uncertain. He said it could be that H. erectus is actually an ancestor to the Denisovans, with Denisovan genes inherited over time rather than arriving only through one episode of intermingling.
Study author Qiaomei Fu, of the Institute of Vertebrate Paleontology and Paleoanthropology in China, pointed to the limitations of what scientists currently have available to test these relationships. “We really need to get more DNA” and additional pieces of H. erectus remains to determine how closely this “predecessor” is related to other humans, Fu said. The researchers said finding more fossils and conducting further tests for remnants of DNA would help firm up the evolving picture of human evolution.