Jaws of Life

A new way to determine biting power may shed light on diets of early humans.

June 07, 2010

By Danny Freedman

A new, greatly simplified method for determining the biting force of animals may offer insights into the diets of early humans, according to researchers.

By analyzing the size of as little as a single tooth, a team of scientists led by GW researchers was able to calculate an animal’s potential maximum biting force. The results, they write, correlated with standard tests using jaw mechanics, a more complex process that requires a near-complete skull.

“What this means is that all you really need is a nice tooth of a species to be able to get some estimate of bite force,” says Paul Constantino, a post-doctoral anthropology researcher at GW and lead author on the study, which was published online last week in the journal Biology Letters.

The new method “opens up a whole new range of species” whose maximum biting power now can be predicted, he says.

The team, which included scientists from the National Institute of Standards and Technology among other institutions, also found that by examining chips in the enamel of teeth they were able to estimate the amount of force that was used to cause that specific incident of tooth damage.

In particular, says Dr. Constantino, the work represents the first time such an estimate has been made for chips commonly found in the teeth of ancient humans, offering insights into what people may have been putting into their mouths millions of years ago.

Although scientists know some early humans—like our toothsome cousin Paranthropus boisei, which appeared 2.3 million years ago—had choppers three-to-four times the size of modern humans’ and enamel that was twice as thick, there is little consensus on what they ate. “It’s gone back and forth,” says Dr. Constantino.

Since the researchers’ tests found that only large, hard objects cause teeth to chip, arguments pointing to grit from a diet of underground tubers and roots are unlikely, says Dr. Constantino. Instead, the researchers felt the culprit probably was a menu that included nuts and seeds, or possibly other hard things like bone.

But if ancient ivories were designed for tough-to-crack diets, why would they chip in the first place?

It’s not quite clear, says Dr. Constantino. But when the researchers examined the teeth of mammals that exist today, they found the highest percentage of chipped teeth per animal in two species that eat incredibly hard seeds: orangutans and pig-like peccaries, which dine on palm nuts that Dr. Constantino says they can be heard cracking hundreds of yards away.

“They might just hit one that’s much harder than what they can handle every once in a while,” he says.

Alternatively, early humans may have had their large teeth and enormous maximum bite force—for example, Paranthropus boisei’s biting power surpassed that of a gorilla, and was nearly two-and-a-half times our own—to get through leanest seasons.

In that theory, it comes down simply to survival when all the usual food sources are scarce. “And if you think about it, that’s what a creature should be adapted for,” says Dr. Constantino. “It’s a hypothesis, but very possible.”

The team now is turning its attention to fractures, or cracks, in teeth—whether the force used to make cracks can be estimated and what that might reveal about diet.

“It’s a whole new way of getting at bite forces in some of these species, and just understanding why teeth are the way they are,” says Dr. Constantino. For example, assuming thick enamel helps protect teeth from fractures, the team is looking into why sea otters have such large teeth with so little enamel, and how they can eat hard foods without breaking teeth.

The work, they hope, could lead to a better understanding of how and why teeth have evolved as they have, which in turn may also inform efforts to mimic biology in the manufacture of stronger materials.

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