Paleontologists across the world have always wondered how the quick change of size, from larger to smaller, happened in human wisdom teeth. But the mystery has been solved by a team of revolutionary biologists from Monash University, Australia. Researchers have discovered that the human teeth evolution is not complex as expected.

The study, lead by biologist Alistair Evans, confirms that molars follow the sizes predicted by what is called “the inhibitory cascade,” a rule that shows how the size of one tooth affects the size of the tooth next to it. Until now, many paleontologists have found large wisdom teeth on prehistoric fossil hominins.

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.

Professor Evans said in a press release,

“Teeth can tell us a lot about the lives of our ancestors, and how they evolved over the last 7 million years. What makes modern humans different from our fossil relatives? 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.”

Prehistoric humans’ teeth became smaller throughout evolution with the wisdom teeth located at the back of the mouth. Wisdom teeth are those four hindmost molars in humans, which usually appear at about the age of twenty. Wisdom teeth are vestigial third molars that helped human ancestors to grind plant tissue. These teeth are most commonly impacted teeth in the human mouth.

However, in modern humans, these teeth are small in size and for many people it doesn’t even develop. In hominin species, these teeth are two to four times larger than the molars in modern humans. This research has revealed that the evolution in wisdom teeth has begun earlier than previously expected. Previous studies have suggested that the shrinking of molars in modern humans was because of the eating habits and diets. Those studies have also mentioned that ancient hominins weren’t cooking food, and they were relying on raw food available on the earth.

Alistair Evans and his team has studied the tooth size in fossil hominins and modern humans and divided the prehistoric humans’ teeth into two major groups. One group was composed of the genus Homo, which includes both modern humans and extinct human relatives. The other group was made up of early hominins preceding Homo, such as the australopiths, the first primates to walk on two feet.

In early hominins (including Ardipithecus, Australopithecus and Paranthropus), the teeth became bigger at the back side, but proportions stayed constant regardless of the overall size of the teeth. However, in the genus Homo, the teeth became smaller toward the back of the mouth.

“It’s always been presumed that sometime in early Homo, we started using more advanced tools,” Evans told Live Science. “Tool use meant we didn’t need as big teeth and jaws as earlier hominins. This may then have increased evolutionary pressure to spend less energy developing teeth, making our teeth smaller.”

The findings of the study will be very useful in interpreting new hominin fossil finds, and looking at what the real drivers of human evolution were. As well as shedding new light on our evolutionary past, this simple rule provides clues about how we may evolve into the future.

The study has been published in the journal Nature.