Wisdom teeth may have shrunk during human evolution as part of changes that started with human tool use, according to a new study.

The research behind this finding could lead to a new way of figuring out how closely related fossil species are to modern humans, scientists added.

Although modern humans are the only surviving members of the human family tree, other species once lived on Earth. However, deducing the relationships between modern humans and these extinct hominins — humans and related species dating back to the split from the chimpanzee lineage — is difficult because fossils of ancient hominins are rare. [Image Gallery: Our Closest Human Ancestor]

Teeth are the hominin fossils most often found because they are the hardest parts of the human body. “Teeth are central to how a fossil ancestor lived, and can tell us about which species they belonged to, how they are related to other species, what they ate, and how quickly or slowly they developed during childhood,” said lead study author Alistair Evans, an evolutionary biologist at Monash University in Melbourne, Australia.

Hominin teeth have shrunk in size throughout evolution, a trend perhaps most clearly seen with the wisdom teeth located at the back of the mouth, the researchers said. In modern humans, wisdom teeth are often very small or do not even develop, while in many other hominin species they were huge, with chewing surfaces two to four times larger than those of their modern human counterparts.

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