The sizes of molars follow a model called the inhibitory cascade, which shows how a tooth's size is affected by the size of the tooth next to it. By taking this into account, researchers studying human teeth were able to discover that human evolution was simpler than previously thought.

To learn more about how humans evolved, an international team of scientists from Germany, United Kingdom, United States and Finland examined the teeth of fossil hominins (extinct close relations) and modern-day humans. Using 3D imaging allowed them to see inside and analyze fossil teeth.

They researchers focused on two main hominin groups: the species in the genus Homo species, which include the Neanderthals and modern-day humans, and the australopiths, which include the famous fossil Lucy from Africa.

Findings showed that both groups followed the inhibitory cascade but in slightly different ways. What is notable is that hominin teeth reduced in size along with human evolution. This trend is most evident in the size of the wisdom teeth.

Modern-day wisdom teeth are smaller and some don't develop at all. In various hominin species, the wisdom teeth are larger and have chewing surfaces that are up to four times bigger than its modern-day counterparts.

Past studies linked the shrinkage to the arrival of cooking methods and dietary changes, which are exclusive to modern-day humans. But the new study suggested it might have started earlier.

"There seems to be a key difference between the two groups of hominins - perhaps one of the things that defines our genus, Homo," said evolutionary biologist Alistair Evans, who lead the research.

The researchers found that australopiths' fossil teeth get bigger toward the back of the mouth. The proportions remained constant despite overall teeth size. In the genus Homo, they found an opposite trend where the teeth get smaller.

The researchers pointed out that the species under the genus Homo used more advanced tools, which made chewing easier. This could have affected the energy spent on developing teeth, which made them smaller.

The study also analyzed teeth data of modern-day humans. Their data included one of the largest dental cast collections from the Adelaide Dental Hospital in Australia.

"These collections of dental casts are critical to finding our place in the hominin evolutionary tree, and advancing knowledge in the oral health of Australians," said Grant Townsend from the University of Adelaide's School of Dentistry.

For many decades, paleontologists have looked for ways to interpret fossil teeth data. The new study proves that scientists can apply the inhibitory cascade mechanism to do so, as well as predict the size of fossil teeth that are missing from human and hominin fossils. The analysis of fossil teeth can help scientists better understand our ancestor's lifestyles and evolution in the past 7 million years.

The new research will help other researchers interpret new hominin fossils to help determine the driving factors behind human evolution. It can also give clues on humans' evolutionary future.

The study was published in the Nature journal on Feb. 24.

Photo: Rupert Taylor-Price | Flickr

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