Dental Analytics Describe Evolution of Human Diet

FAYETTEVILLE, Ark. — University of Arkansas anthropology professor Peter Ungar spends hours crouched in forests in remote locations studying monkeys; he uses dental techniques to create molds of teeth; and he uses modern-day technology to study the wear and tear on those teeth to look at what modern-day primates eat — and for clues as to what our ancient human ancestors actually ate.

Ungar will be part of a seminar that includes a panel of experts addressing different aspects of the evolution of human diet. The seminar is part of the American Association for the Advancement of Science meeting on Friday, Feb. 13, in Chicago.

“Teeth are perfect for testing diet hypotheses, because they are the best preserved items in the fossil record and are part of the digestive system,” said Ungar. “But until now, we haven’t had the technology to pull much information out of them.”

His work has found anatomical evidence to support some long-standing hypotheses — and in other cases has found evidence that suggests the current models are wrong.

“The models are fine in and of themselves, but we need to go further,” Ungar said. “We need to test them as hypotheses.” With his pioneering techniques, he has found a way to do just that.

Until recently, scientists counted the pits and scratches on teeth by looking at images from high-resolution electron microscopes. But such counts depended upon the expertise of the observer and often proved difficult to reproduce.

“The problem then is that you have to count and measure those features by hand, which introduces a high likelihood of human error. That's a very subjective process, and you're going to get variability between the measurements of any two researchers” Ungar said. “We needed an objective, automated, repeatable way to quantify wear on teeth.”

Ungar sought a more objective way to look at the wear and tear on teeth. He first developed a way of using software for geographic information systems to create a different kind of map — he used the software for dental topography, to show the mountains and valleys formed by the wear patterns on teeth. Just as GIS can be used to measure topographical features on a landscape, such as slope, elevation and aspect, Ungar found it could analyze dental features that are important to chewing and processing foods. In particular, Ungar and his colleagues used GIS to calculate slope and angularity values for each tooth; slope refers to the steepness of a tooth cusp, whereas angularity is a measure of overall jaggedness.

In 2003, Ungar increased the resolution of his measurements by using a white light scanning confocal microscope. The length, width and even depth information about specific features is automatically and objectively recorded by the instrument.

The detailed, three-dimensional information allows researchers to determine characteristics of the surface, such as roughness and directionality of the wear using fractal analyses borrowed from mechanical engineering.

Ungar combines his high-tech work with old-fashioned fieldwork. He has logged thousands of hours in forests in Central and South America as well as Indonesia observing the diets of different apes and monkeys. Researchers can then tranquilize or examine museum specimens of the animals and use the same dental techniques employed to make crowns to create high-resolution molds of primate teeth using epoxy. Ungar also has created dental impressions of some of the world’s most famous fossil ancestors, including AL-288-1, better known as “Lucy,” the famed Taung child, and OH-5, known as “Nutcracker Man.”

This work has resulted in a repository of hundreds of tooth impressions. Using this library of teeth, he can compare what modern-day primates eat and the wear patterns on their teeth to the wear patterns on fossil teeth to get direct evidence of what types of foods they were eating.