Wisdom teeth or those six molar teeth in our jaw can take a long time to appear in some people. While they may “erupt” in children as young as six years old, in others, they practically appear in adulthood.

Now, new research that analyzed primate skulls provides the first clear answer.

In a paper published in the journal Science Advances, researchers at the Arizona State University have revealed that shorter jaws, retracted faces and slow body development in humans might explain why molars appear so late.

“One of the mysteries of human biological development is how the precise synchrony between molar emergence and life history came about and how it is regulated,” said Halszka Glowacka, lead author of the paper, and an anthropologist.

The researchers gathered skulls of 21 different primate species and tuned the bones and teeth into 3D models for comparison. Turns out, the appearance of the adult molars is determined by the delicate balance of biochemicals in growing skulls,

In Humans, molars used to grind food usually appear in three stages at roughly six, twelve, and eighteen years of age. On the other hand, Chimpanzees, although similar in other biological growth to humans, get their molars far earlier, at three, six, and twelve years of age.

The Yellow Baboon gets all its molars by the age of seven, while the Rhesus Macaque will have a full set of teeth by age six.

According to the researchers, the biggest constraint for the molars to appear is space within the jaw. Growing up, humans do not have the big enough jaw to accommodate a full set of adult-sized teeth, unlike other primates.

“It turns out that our jaws grow very slowly, likely due to our overall slow life histories and, in combination with our short faces, delays when a mechanically safe space – or a ‘sweet spot,’ if you will – is available, resulting in our very late ages at molar emergence,” said Gary Schwartz, assistant author of the paper, and a paleoanthropologist at the University of Arizona’s Institute of Human Origins.

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