Ancient proteins extracted from a 400,000-year-old tooth have connected three chapters of human prehistory in a single study. Researchers identified molecular evidence linking Homo erectus in China to the Denisovans and, through them, to modern humans living today.
The team analyzed enamel proteins from six Homo erectus teeth recovered from three Chinese sites: Zhoukoudian in northern China, Hexian in the south, and Sunjiadong in central China.
Researchers also included a tooth from the Harbin skull, a known Denisovan specimen from northeastern China. All six Homo erectus specimens date to roughly 400,000 years ago, and five were identified as male while one was female.
Six teeth, three sites, and a rare molecular find
Two protein variants stood out. The first, AMBN(A253G), has never been detected in any other human or primate species. It was absent in Neanderthals, Denisovans, modern humans, and even other Homo erectus specimens from Dmanisi in Georgia and Atapuerca in Spain.
Its presence across all six specimens from three geographically separate sites suggests it was specific to this particular group of East Asian Homo erectus.
The second variant, AMBN(M273V), carries bigger evolutionary implications. Researchers already knew this variant existed in Denisovans. Its presence in all six Homo erectus specimens now points to these ancient humans as the likely original source.
Earlier Denisovan specimens, including Harbin and a roughly 200,000-year-old individual called Denisova 25, carried this variant in a mixed form, meaning only some copies of their DNA had it. Later, Denisovans carried it exclusively.
Fu and colleagues say this pattern suggests the variant entered Denisovan populations gradually through contact with groups related to these Middle Pleistocene Homo erectus.
The tooth that puts homo erectus among the Denisovans
Previous genomic research had already shown that Denisovans received between 0.5 and 8 percent of their DNA from an older, unidentified human lineage whose ancestors split from the main human family tree more than one million years ago. The researchers now identify Homo erectus as the most likely candidate for that unknown lineage.
Around 15 percent of that ancient DNA later passed from Denisovans into modern human populations across Asia and Oceania. Today, the variant appears in 21 percent of people in the Philippines, and at lower frequencies in India and Papua New Guinea.
The timing also fits. Denisovans are believed to have split from Neanderthals between 380,000 and 470,000 years ago, roughly the same period when these Homo erectus individuals lived across China.
Shared geography and overlapping timelines made interaction between the two groups not only plausible but now molecularly supported. The study, published in Nature, was led by Qiaomei Fu of the Chinese Academy of Sciences in Beijing.
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