Humanity’s genealogy has become much clearer thanks to our ability to obtain ancient DNA. We now know that, as humans left Africa, they interacted with the groups they found there, the Neanderthals and Denisovans. Evidence from the Denisovan genome also suggests that this was nothing new; The Denisovans apparently interacted with an even earlier group. But the identity of that group remained a bit of a mystery.
Now, some evidence from ancient proteins suggests that the mystery group was homo erectusA species that left Africa one million years ago and spread throughout Eurasia. And, thanks to the Denisovans, modern humans appear to have inherited some of them homo erectus DNA.
in the teeth
Without access to all the repair enzymes made by living cells, DNA rapidly degrades. Fragments and bases of the double helix change identity or collapse completely. While the cold, dry environment slows this process, it sets a hard limit on how far back we can get DNA sequences. So far it seems like this homo erectus Remains at the far end of the range at that time.
To avoid these limitations, people have turned to protein. While they also degrade over time, there are some structures, such as bone and teeth, that are very strong and protect the proteins from the environment. For example, by studying the proteins in tooth enamel, researchers have obtained the amino acid sequences of protein fragments that are 2 million years old.
Given these previous successes, a group of Chinese researchers decided to use microscopic samples homo erectus The teeth, recovered from three sites in China, each date back about 400,000 years. They began taking samples from animals at the same location and confirmed that they were able to separate and identify protein fragments from tooth enamel. Once they were confident in their process, the researchers turned to five homo erectus Took samples and also sent a Denisovan from Harbin.
depends on which of the six homo erectus The people they looked at received anywhere from six to 11 pieces of enamel protein. The Harbin individual yielded a similar number, and some earlier studies had obtained data from individuals elsewhere, including a Denisovan from near Taiwan and an archaic human from Spain.
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