Researchers in China have extracted proteins from the tooth enamel of Homo erectus fossils from China. The findings suggest a possible connection with Denisovans, and an indirect transfer of some of this heritage to modern populations in Southeast Asia and Oceania.
A new study published in the journal Nature adds an important layer to the increasingly complicated picture of human evolution. For many years, it was customary to describe human development as an orderly tree: ancient species branched off into separate branches, and some went extinct without leaving descendants. But in recent decades, ancient DNA studies have repeatedly shown that the picture resembles less a tree and more an intricate network of encounters, intermingling, and gene transfer between ancient human groups.
Now, research suggests that Homo erectus, one of the most important early human species, may not have been an evolutionary “dead end.” The researchers extracted ancient proteins from the tooth enamel of six Homo erectus fossils from three sites in China: Zhuokoudian, identified with “Peking Man,” Hexian, and Songjiadong. The fossils date back to about 400 years ago. Since DNA rarely survives such long periods of time under these conditions, the researchers relied on tooth enamel proteins, which are much more durable.Nature)
When the tooth replaces the DNA
The researchers, led by Xiaomi Fu of the Chinese Academy of Sciences, identified two variations in the protein ameloblastin, a protein involved in the formation of tooth enamel, in the teeth of Homo erectus. One of the variations, AMBN(A253G), was found in all six samples and had not previously been documented in any other ancient or modern humans. According to the researchers, it may serve as a unique molecular marker for Homo erectus populations that lived in East Asia during the Middle Pleistocene.
The finding is also important because it helps resolve a long-standing debate over the identity of the Ha-Shin fossils. In the past, some researchers have suggested that the fossils may be related to Denisovans, a mysterious group of early humans known mainly from genetic evidence. However, the protein pattern found in the study places the Ha-Shin teeth with Homo erectus teeth from other sites in China, thus strengthening their association with Homo erectus.
A surprising connection to the Denisovans
The second variation, AMBN(M273V), is even more intriguing. It has been found in both Homo erectus and Denisovans’ teeth, and also occurs at low frequencies in some modern humans. According to the Nature paper, the corresponding genetic variant occurs at a frequency of about 21% in the Philippines, 1.17% in India, and 0.71% in Papua New Guinea, and is almost absent in most other human populations.
The researchers' cautious interpretation is that this variation did not originate in the Denisovans themselves, but was passed on to them from a population close to Homo erectus in East Asia. Later, when Denisovans mated with the ancestors of modern humans in Asia and Oceania, some of this legacy was passed on to us as well. That is, it is possible that a small molecular trace from Homo erectus survived in modern humans, not directly but through the Denisovans.
It is important to emphasize: The study does not claim to have discovered Homo erectus DNA in modern humans. It points to a pattern in ancient tooth proteins and a parallel genetic variant in Denisovans and some modern populations. Therefore, this is indirect, but significant, evidence of admixture between ancient human groups.
Not a family tree but a tangled web
Homo erectus is considered one of the first human species to leave Africa and spread across large areas of Eurasia. It appeared about two million years ago and was one of the longest-lived and most geographically widespread human species. Until now, the lack of reliable DNA from Homo erectus fossils has made it very difficult to understand its exact place in human evolution.
The new study joins a series of studies that have shown that admixture between ancient human populations was much more common than previously thought. Modern humans outside Africa carry an average of about 2% Neanderthal DNA. Populations in Papua and Australia also have a more significant Denisovan component. In West Africa, genetic evidence of an as-yet-unidentified ancient population has been found. According to an analysis by Sally Christine Reynolds of Bournemouth University in The Conversation, the new finding reinforces the idea that human origins were not a pure process of replacement, but a long history of encounters and the transfer of traits between different groups.
The broad implication is that our genes are a mosaic. They do not come from a single, continuous evolutionary line, but include contributions from ancient groups that lived in different regions and adapted to different environments. It is not yet clear whether the variation that may have originated in Homo erectus had a functional significance, such as environmental adaptation or some other biological effect. The researchers note that this is an open question for future research.
A new window into “ghost” populations
One of the study's important contributions is technological. Tooth enamel proteins survived where DNA did not. If proteins can be extracted from 400-year-old Homo erectus fossils, it may be possible to apply similar methods to fossils of other ancient human groups that have not yielded DNA, such as Homo floresiensis on the island of Flores or Homo luzonensis in the Philippines.
In this sense, the study not only suggests a possible connection between Homo erectus, Denisovans, and modern humans. It also opens up a new way to study almost inaccessible chapters in human evolution. A tiny protein preserved in an ancient tooth may become evidence that connects “Peking Man” with populations living today in Southeast Asia and Oceania.
Short FAQ
What did the researchers discover?
The researchers extracted proteins from the tooth enamel of six Homo erectus fossils from China, and identified molecular variations that link them to Denisovans.
Why didn't they test DNA?
Ancient DNA decays over time, and in fossils hundreds of thousands of years old it is often not preserved. Tooth enamel proteins are more durable and therefore could serve as an alternative source of information.
Does Homo erectus live on in modern humans?
Not in a direct sense. The study suggests that a variation that possibly originated in Homo erectus passed to Denisovans, and from there to the ancestors of some modern humans in Asia and Oceania.
What is the importance of the research?
The study reinforces the understanding that human evolution was not a straight line, but a network of encounters and transfer of traits between ancient human groups.
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