Ancient Teeth Show Homo erectus Left Genetic Traces in Living People
Protein analysis of ancient enamel points to mixing between early human groups that may still be visible in living populations.
Key points
- Researchers recovered proteins from six Homo erectus teeth from three sites in China, dated to about 400,000 years ago.
- A shared amino acid variant places the east Asian fossils in a distinct group and helps settle the Hexian debate.
- A second variant also appears in Denisovans and is found in living people at about 21% in the Philippines.
- The study suggests interbreeding between archaic human groups was common, not rare.
- Homo floresiensis and Homo luzonensis have still not yielded any molecular data.
Scientists have recovered ancient proteins from teeth about 400,000 years old, and the results point to a more tangled history for early humans. According to ScienceDaily, the study was led by Qiaomei Fu of the Chinese Academy of Sciences and colleagues and published in the journal Nature. It reports molecular information from Homo erectus, a species whose fossils are too old for DNA analysis.
The team examined enamel from six teeth found at three sites in China: Zhoukoudian, Hexian and Sunjiadong. Zhoukoudian is the site where fossils known as Peking Man were first found in the early 20th century. Tooth enamel is very hard, and its proteins can persist long after DNA has broken down beyond recovery.
A shared molecular signature
All six specimens carry an amino acid variant that has not been seen in any other hominin, living or extinct. The team says this marker places the east Asian fossils in a distinct group. It also helps resolve a long debate about whether the Hexian remains belonged to Homo erectus.
A second variant found in the teeth is not unique to Homo erectus. It is also present in Denisovans, an archaic group known mainly from a single cave in Siberia. In living people, the matching genetic variant appears at about 21% in the Philippines and roughly 1% in India. Based on this pattern, the researchers propose that Homo erectus populations in east Asia shared the variant with Denisovans via mating between the groups, and that Denisovans later handed it down to the forebears of people in south-east Asia and Oceania.
Interbreeding as a common pattern
The researchers say the wider significance is that mixing between archaic human groups appears to have been common. People outside Africa carry about 2% Neanderthal DNA. Papuans and Aboriginal Australians have an additional 2 to 5% of Denisovan ancestry. West African populations carry signals from an unidentified archaic lineage.
A 2019 review in the American Journal of Physical Anthropology, cited in the report, describes at least three separate gene flow events from Denisovan-like groups into south-east Asian and Oceanic ancestors. Some of these may have occurred as recently as 20,000 years ago. Denisovans themselves appear to have received genetic material from an older and more distant source, likely Homo erectus.
Open questions
The function of the Homo erectus-derived variant is not yet known. Some Denisovan-derived variants in Papuan genomes seem to affect immune function, which suggests such exchanges may have helped groups adapt to new environments. The study does not confirm that the newly identified variant plays a similar role.
The findings also raise questions about other lineages. Homo erectus persisted in Indonesia up to roughly 100,000 years ago. Homo floresiensis, nicknamed the hobbit, lived on Flores when modern humans arrived, and Homo luzonensis lived in the Philippines. No DNA has been recovered from either species, and neither had yielded any molecular data until now. The authors suggest that protein analysis could one day test whether they also contributed to later human populations.
The picture that emerges is less like a single trunk with separate branches and more like a braided river, with many channels that merge and split. As the researchers put it in their reading of the evidence, ancient populations that disappeared may still have left traces in people alive today.
Frequently asked questions
What did the study find in the Homo erectus teeth?
Researchers recovered ancient proteins from enamel of six teeth from three Chinese sites, dated to about 400,000 years ago. The proteins revealed a shared amino acid variant that places the fossils in a distinct group.
Did Homo erectus interbreed with Denisovans?
According to the study, a second variant found in the teeth also appears in Denisovans. The most likely explanation is that it passed from Homo erectus to Denisovans through interbreeding, and later to people in south-east Asia and Oceania.
Where was the research published?
The study was published in the journal Nature and was reported by ScienceDaily. It was led by Qiaomei Fu of the Chinese Academy of Sciences and colleagues.
Sources
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