Protein in Homo erectus teeth suggests Denisovans gave us some of their DNA

"Without access to all the repair enzymes made by living cells, DNA rapidly degrades. The double helix fragments, and bases change identity or fall off entirely. While cooler, drier environments slow this process, it sets a hard limit on how far back in time we can obtain DNA sequences. So far, it seems that Homo erectus remains on the far side of that time limit."

"To get around these limits, people have turned to proteins. While those also degrade over time, there are a few structures, like bone and teeth, that are very robust and protect proteins from the environment. By studying proteins in tooth enamel, for example, researchers have obtained the sequence of amino acids from fragments of proteins that are 2 million years old."

"Given these past successes, a group of Chinese researchers decided to use microscopic samples of Homo erectus teeth from three sites in China, each dating to about 400,000 years ago. They started by taking samples from animals at the same site and confirmed they were able to isolate and identify protein fragments from the enamel of the teeth. Once they were confident in their process, the researchers turned to the five Homo erectus samples and threw in a Denisovan from Harbin as well."

"And, thanks to the Denisovans, it appears that modern humans inherited some of that Homo erectus DNA."

Ancient DNA has clarified human ancestry by showing that humans interbred with Neanderthals and Denisovans after leaving Africa. Denisovan genetic evidence also suggests interbreeding with an even earlier group, though that group’s identity was unclear. DNA degrades over time, limiting how far back sequences can be recovered, so researchers use more durable biomolecules such as proteins preserved in enamel and bone. Tooth enamel can protect protein fragments, allowing amino-acid sequences to be recovered from very old samples. Chinese researchers analyzed microscopic samples from Homo erectus teeth in China dated to about 400,000 years ago, validated their methods using animal samples, and then compared five Homo erectus individuals with a Denisovan sample from Harbin. Protein evidence indicates that Denisovans had ancestry involving Homo erectus, and modern humans inherited some of that Homo erectus genetic material.

Read at Ars Technica