Human Bite Stronger Than Thought

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THE GIST

- It has long been thought that modern humans lost the ability to generate a powerful bite.

- New analysis shows our bite is much more powerful than scientists thought.

- The mechanics of the modern human jaw is highly efficient.

Humans have a much more powerful bite than previously thought, thanks to the mechanics of their skull, say Australian researchers.

Stephen Wroe from the University of New South Wales in Sydney and colleagues reported their comparison of human and other skulls recently in the Proceedings of the Royal Society B.

"The traditional view is that modern humans have lost the ability to generate a powerful bite," said Wroe.

He said this has been driven by the fact that humans have relatively weak jaw muscles and lightweight skulls, compared to our fossil ancestors and living great apes.

Some scientists argue a weaker bite evolved in response to humans eating softer foods, processing them with tools and cooking.

But, said Wroe, there has been no direct data to support these conclusions. He said the very thick tooth enamel coating human teeth is generally associated with processing hard foods in primates.

Wroe and colleagues used sophisticated engineering software to compare the maximum bite force of modern humans with that of four living apes (chimpanzee, gorilla, orangutan and gibbon) and two fossil hominids (Australopithecus africanus and Paranthropus boisei -- also known as "nut-cracker man").

They used a method called 3D finite element analysis to study digital models of skulls that had been CAT-scanned.

The researchers simulated a scenario in which the animal was biting a hypothetical hard object with its back teeth, and visualized how stress was distributed.

"When you actually look at the mechanics of it, the human jaw is highly efficient," said Wroe.

"For any given bite force you want, we can achieve it with much less muscle."

The researchers say the design of the human jaw makes it 40 percent to 50 percent more efficient than for all great apes.

"Pound for pound we're actually biting harder than a gorilla or a chimpanzee," said Wroe, adding there's no big difference between the bite force of a human and the nutcracker man, once body size is allowed for.

Wroe said it basically comes down to leverage.

"It's about how long the jaw is. It's about where the fulcrum is -- or the jaw joint in this instance. And where the muscles attach and the way they are arranged," he said.

While humans are capable of a powerful maximum bite force, which is useful for cracking nuts or biting into meat, they are less well adapted for hours of chewing tough leaves and bamboo tubers, said Wroe.

"So we certainly have lost some of the capacity that great apes have," he said.

"But we have not strongly compromised our ability to either crack a hard item or bite off a good chunk of flesh."

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