An international team of scientists has found that a distant relative of modern humans had dental growth that was very similar to our dental development today. The hominin fossil examined for the study, known as the Xujiayao juvenile, belonged to a six-year-old child who lived between 104,000 and 248,000 years ago.
Study co-author Debbie Guatelli-Steinberg is a professor of Anthropology at The Ohio State University. She said that the researchers were surprised to find that in most ways, this child’s dental development was very similar to what you would find in a child today.
“The Xujiayao juvenile is the oldest fossil found in east Asia that has dental development comparable to modern humans,” said Professor Guatelli-Steinberg. “It may suggest that these archaic humans had a slow life history like modern humans, with a prolonged period of childhood dependency.”
According to Professor Guatelli-Steinberg, teeth provide some of the best data about the growth and development of our ancient ancestors. This is due to the growth lines in teeth, which hold a record of dental development.
Compared to primates, modern humans take a long time to develop. Experts theorize that human growth is prolonged because children rely on caregivers for a longer period of time.
The team used synchrotron X-ray imaging to examine the internal structure of the teeth, including the growth lines. The findings were unexpected because so many other features of this hominin are not modern, such as the shape and thickness of the skull.
“We don’t know exactly where this enigmatic East Asian hominin fits in human evolution,” said study lead author Song Xing from the Chinese Academy of Sciences. “It has some affinities to archaic human relatives like the Denisovans and Neanderthals with, as we found, some more modern features. It is a strange mosaic.”
The first molar of the Xujiayao juvenile had erupted a few months before death and the root was about three-quarters complete, which is on the same schedule as modern humans. The incremental growth lines that appear on the surface of the tooth, known as the the perikymata, were also like those of modern humans.
“We found that the way these perikymata were distributed on the Xujiayao juvenile teeth was close to what we see in modern humans, and not to Neanderthals,” said Professor Guatelli-Steinberg.
The study is published in the journal Science Advances.