The case of Xujiayao, an archaic child with modern dental development

The case of Xujiayao, an archaic child with modern dental development

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A archaic East Asian hominin, known as the boy of Xujiayao, had a tooth growth very similar to that of today's people.

Researchers from China, the United States, Spain, France, the United Kingdom and South Africa have carried out the first systematic evaluation of dental development in its fossil, which corresponds to that of a six-and-a-half-year-old boy who lived between 104,000 and 248,000 years ago at the site of Xujiayao, north of China.

«The young Xujiayao is the oldest fossil found in East Asia with dental development comparable to that of modern humans. What it may indicate is that these archaic humans had a slow life history like modern humans, with a prolonged period of childhood dependency, "says Debbie Guatelli-Steinberg, co-author of the study and professor of anthropology at Ohio State University. UU). The study is published in the journal Science Advances.

Growth lines on teeth keep a record of tooth progression, providing data on the development of our ancestors. Compared to other primates, modern humans, including their teeth, take a long time to form and develop. Anthropologists believe that this characteristic is associated with longer periods of dependence on the support of a caregiver.

"Until now, Homo sapiens members consider ourselves unique, due to the fact of having a slow and complex development, which ends around the age of 18. No living primate has all four periods of our development: infancy, childhood, youth phase and adolescence”, Says José María Bermúdez de Castro, researcher at the National Center for Research on Human Evolution (CENIEH). Instead, this new discovery suggests that we are not as unique as we had thought.

Xujiayao's other traits are archaic.

The juvenile maxilla retains seven teeth at different stages of development. The team of researchers studied the relative developmental status of this individual with respect to that of a modern human of the same age, not an easy task.

Scientists had to resort to very complex techniques, such as the great Phase Contrast Synchrotron Facility in Grenoble (France). Other tools such as computed microtomography or micro-CT were also used, and the results were supported by previous work on other fossils.

The results were surprising in part because many other characteristics of this hominid are not modern, such as the shape and thickness of the skull and the large size of the teeth. "According to what we knew so far, humans in the late Middle Pleistocene had a more accelerated development than ours," says the CENIEH scientist.

"We don't know exactly where this enigmatic East Asian hominin fits into human evolution," says Song Xing, lead author of the study at the Chinese Academy of Sciences in Beijing.

This specimen has some similarities to Denisovans and Neanderthalsas well as some more modern features. "It's a strange mosaic," he adds.

This child's first molar, what is now called the six-year-old molar, had come in a few months before death and began to wear down a bit. Three-quarters of the root were complete, something very similar to what happens in humans today.

"This young man was growing, dentally at least, with a development similar to modern people," explains Mackie O'Hara, a co-author of the study and an anthropologist at Ohio University.

Although the dental development of this juvenile suggested that it had a slow life course similar to that of modern humans, Guatelli-Steinberg cautioned that you can't tell what happens next. "It would be interesting to see if dental development in later childhood, such as third molars, was also similar to humans today," he concludes.

Bibliographic reference:

“First systematic assessment of dental growth and development in an archaic hominin (genus, Homo) from East Asia” Song Xing, Paul Tafforeau, Mackie O'Hara, Mario Modesto-Mata, Laura Martín-Francés, María Martinón-Torres, Limin Zhang , Lynne A. Schepartz, José María Bermúdez de Castro, Debbie Guatelli-Steinberg, Science Advances

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