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Ancient teeth offer intriguing theory of human relative

From 1972 to 1983, anthropologists found four ancient teeth in a cave in Yanhui, China. At first, the teeth were classified as belonging to Homo erectus, a human ancestor who lived in China hundreds of thousands of years ago.

Recently, a team of scientists began to question that conclusion, and they’ve uncovered a real mystery.

Using new analytical techniques, the researchers from the Chinese Academy of Sciences, the Centro Nacional de Investigación sobre la Evolución Humana and University College London have come to the conclusion that the more than 200,000-year-old teeth don’t belong to Homo erectus, or to the Neanderthals who followed them.

“It’s strange. We don’t know where to put it,” study author Dr. Song Xing told National Geographic.

The teeth aren’t the first hominid fossils found in Asia that don’t really seem to fit anywhere on the known human evolutionary tree.

“We always think of Africa as the ‘cradle of humankind,’” study author Dr. María Martinón-Torres said.

But that collection of Chinese and other Asian fossils, including the ancient teeth, show that evolution didn’t stop when human ancestors left Africa – and there is a lot to learn in Asia.

The researchers used a technique called micro-computed tomography to analyze the Yanhui teeth, from structure to surface details. Then, they compared that data to ancient teeth from Africa and throughout Eurasia.

Four ancient teeth found in Yanhui, China in the 1970s and 1980s were recently reanalyzed using modern techniques. Image credit: Dr. Song Xing, Chinese Academy of Sciences.

Four ancient teeth found in Yanhui, China in the 1970s and 1980s were recently reanalyzed using modern techniques. Image credit: Dr. Song Xing, Chinese Academy of Sciences.

They found a lot more matches than they thought – in parts. The Yanhui teeth shared a mishmash of traits with both Homo erectus, Neanderthal and later hominid teeth, while lacking some of the important features that could place them solidly in one category.

That points to the possibility they came from other human ancestors, who are known to have lived through Asia and Oceania, from Siberia to Papua New Guinea: Denisovans.

Denisovans are believed to have split from the Neanderthal branch of the human tree about 300 generations after Neanderthals and the branch that would become modern humans began to grow apart.

A handful of remains from Denisovans and possible Denisovan-Neanderthal hybrids were found Denisova cave in Siberia. Archaeological sites in Tibet offer intriguing clues pointing to Denisovan occupation. But they’re mostly recognized by their distinct DNA, found throughout Asia, especially in the Pacific Islands. Not much is known about the cousins of modern humans.

The Siberian cave also held some ancient teeth, but they were from a different position in the mouth than the Yanhui teeth, so they can’t be directly compared.

The Yanhui teeth might be from the mysterious Denisovans. Or they might be an entirely new human cousin, or a hybrid of Neanderthal and Denisovan or Neanderthal and Homo erectus. There are any number of possibilities.

Anthropologists not involved with the study agree the teeth are distinct from both Homo erectus and Neanderthals, but like Xing and Martinón-Torres, they don’t know how to classify them.

“I am sure that there is Denisovan material out there,” Dr. Shara Bailey, a dental paleoanthropologist from New York University, told National Geographic. “The thing is, is that until we have good comparative cranial and mandibular material, it’s just a guessing game.”

The study is encouraging anthropologists to take another look at Chinese fossils, including more ancient teeth found in Panxian Dadong and Xujiayao, and skull fragments from throughout the country. In the past, studies haven’t always been translated from Chinese to other languages, but that’s beginning to change.

And that’s important, Martinón-Torres said, because understanding human evolution in Asia is  “crucial to understanding the whole picture.”

The study has been published in Journal of Human Evolution.

By Kyla Cathey, staff writer

Image credits: Dr. Song Xing, Chinese Academy of Sciences; Shutterstock

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