RESEARCHER CHARTS DENTAL LANDSCAPES AND DIET’S EVOLUTION

FAYETTEVILLE, Ark. - University of Arkansas anthropologist Peter Ungar has found a way to use computer mapping techniques to chart the landscape of teeth and learn how the human diet might have evolved. His insights into "dental landscapes" may help solve today’s diet-related health problems.

Ungar and his colleagues use Geographic Resources Analysis Support System (GRASS) software to examine teeth from gorillas, chimpanzees, orangutans and ancient human fossils, they reported in the American Journal of Physical Anthropology.

Ungar clicks a key on his computer and a red laser beam moves over a small tooth. The laser reads coordinates in three dimensions at 1/1000^th -inch slices along the tooth’s surface. The GRASS software then calculates coordinates in three dimensions and produces a map outlining the tooth’s shape.

"GRASS allows us to look at things no one has ever looked at before," Ungar said. "The technique gives you numbers and lets you get at very fine distinctions."

The teeth are treated like any landscape surface. Ungar points out the "mountains" and "valleys," which can be viewed from different angles. The precise computer-calculated numbers allow researchers to determine the slope of a given tooth curve. Another computer program shows researchers how food and liquid might accumulate or drain over the tooth’s surface - important to understanding tooth function.

The addition of GRASS to Ungar’s tool box enables him to better chronicle the evolution of human diet by studying the form and function of primate and human fossil teeth.

"With this new technique we can get even finer distinctions in diet," Ungar said.

Ungar’s colleagues have spent months crouched in Costa Rican forests, watching howler monkeys eat. He and his fellow researchers then tranquilize the monkeys and make casts of their teeth, using the same materials a dentist presses on human teeth to make impressions for crowns. The researchers return to the laboratory to make casts from the molds and study the teeth.

The shape, size and wear on the monkeys’ teeth correspond to their diet. For instance, primates that eat leaves and meat have sharp teeth for tearing and shredding and telltale scratches on the tooth enamel. Monkeys that eat nuts, beetles and other hard, brittle foods have broader, flatter teeth that display small pits.

The howler monkey study spans two decades, so the scientists involved can see how the teeth have worn with time. Using the GRASS technology, they also can distinguish subtle dietary differences between howlers living in grassland or along riverbanks, Ungar said.

After examining these teeth on a microscopic level and relating their dental characteristics to diet, Ungar looks at early hominid teeth in the same manner. He and other researchers can then infer what early homonids ate.

Used with fossils throughout the evolutionary record, these findings paint a picture of what the human body evolved to eat - a portrait that looks little like what the average American eats today.

"We didn’t evolve to eat cheeseburgers and milkshakes, that’s for sure," Ungar said.

Human ancestors consumed fewer grains and more fruits and vegetables, getting more protein, vitamins, minerals and fiber than people in affluent societies do currently.

As humans grew grains, developed alcohol, cultivated sugar and mined salt, dietary changes began to evolve so fast that their anatomy could not adapt. This has led to chronic diseases caused by dietary discord - cancer, diabetes, high blood pressure and heart disease.

The more researchers can determine about what humans evolved to eat, the better people will understand the consequences of the food they pop in their mouths, Ungar said.

For research summaries from different institutions on human evolution and diet click here.