Protein in Homo erectus Teeth Indicates Denisovan DNA Inherited by Modern Humans

Analysis of ancient proteins extracted from Homo erectus teeth has provided evidence that Denisovans interbred with this earlier human relative and passed some of that genetic material to modern humans. Homo erectus left Africa more than a million years ago and spread across Eurasia.

Previous genetic studies indicated that Denisovans carried DNA from an even earlier archaic human group. The identity of that group had remained unclear until the protein evidence pointed to Homo erectus. DNA degrades over time and becomes difficult to recover from remains older than several hundred thousand years.

Proteins preserved in tooth enamel last longer, allowing researchers to recover amino acid sequences from samples up to 2 million years old. The researchers collected microscopic samples from Homo erectus teeth recovered at three sites in China, each dated to about 400,000 years ago.

They first validated their methods on animal teeth from the same locations before examining five Homo erectus specimens and a Denisovan tooth from Harbin. From these samples they recovered fragments of six to 11 enamel proteins per individual. The team compared the ancient protein sequences with those found in modern humans and required that any differences appear in multiple overlapping fragments analyzed at two separate facilities.

Two amino acid differences were identified in the protein ameloblastin. One variant appears unique to Homo erectus among primates studied so far. The second variant was found in one copy of the protein in the Harbin Denisovan, alongside a version matching that of modern humans.

The genetic change responsible for this second variant has been detected in the genomes of other Denisovans as well as in several modern human populations, including groups in India, the Philippines, and elsewhere. It is present in more than 20 percent of some populations native to the Philippines.