Fossil Teeth May Offer Evidence Of Meat Eating In Early Human Ancestors

FAYETTEVILLE, Ark. — An examination of tooth shape in the earliest members of the human genus reveals a change in diet to tougher foods — possibly the first anatomical evidence of a shift toward regular meat eating, says University of Arkansas anthropologist Peter Ungar.

Using Geographic Information Systems (GIS) to model the surfaces of teeth as though they were landscapes, Ungar has pioneered a new methodology for analyzing tooth shape and wear patterns in relation to food consumption. His latest study compares the slope and relief of teeth from two early human ancestors — Australopithecus afarensis, the Lucy species, and early Homo, first members of the human genus.

Ungar’s analysis showed that Australopithecus afarensis had shallower slopes on their teeth, in other words, less steep cusps with less shear. This tooth shape suggests a diet of brittle foods, including nuts, seeds, roots and tubers. But the teeth of early Homo showed significantly steeper slopes with greater shearing power.

"There’s a distinct anatomical change between Australopithecus and Homo. Something was driving early Homo to develop sharper crests on their teeth," Ungar said. "What causes primates to develop sharper crests? The consumption of tough foods. We can’t say exactly which tough foods, but it’s a reasonable hypothesis that it was meat."

Ungar presents the findings of this study tomorrow at "The Evolution of Human Diet," a symposium hosted by the University of Arkansas and funded by the Alfred P. Sloan Foundation.

Archeological evidence and findings from bone chemistry studies have argued for the early consumption of meat among human ancestors. But Ungar’s data are the first to anatomically pinpoint the shift to regular meat eating with the rise of the Homo species, about 2.5 million years ago.

"Early Homo were the first undisputed tool makers, the first to live in the open savannah, the first with evidence of a more terrestrial-based lifestyle. There’s been an assumption that this is where meat eating took off, in part because this is when we start to find cut marks on animal bones in the archeological record," Ungar explained. "But these ideas have been difficult to test, partly because there’s been no way to look at teeth and determine whether anatomy reflected a dietary shift."

Because of their direct physical interaction with foods, teeth are the best clues scientists have to the diets of human ancestors. Tooth size and shape can indicate the types of food that species were best able to process. Unfortunately, early researchers set the standard for dental analysis using unworn teeth, which are rarely found in the fossil record. No quantitative method of examining worn teeth was available prior to Ungar’s work.

Ungar’s technique uses resin casts of fossil molars, which he scans with a laser to record point by point elevation data across tooth surfaces. GIS software enables Ungar to compile the data into 3-D models of the teeth. These models can be measured for slope and angularity, just as topographical features on a landscape can be measured.

In his latest article "A Solution to the Worn Tooth Conundrum," published in the April 1 issue of Proceedings of the National Academy of Sciences, Ungar used the methodology to examine gorilla and chimpanzee teeth. Using multiple tooth specimens, Ungar discovered that even as teeth wear down from use, they maintain the values of slope and angularity that are characteristic to each species.

Therefore, despite the fact that his study of Australopithecus afarensis and early Homo examined worn fossil teeth, Ungar can be certain that the morphological differences are species-specific and not the result of mechanical wear.

The findings could bolster the arguments of those who claim humans were "designed" to eat meat from our earliest stages of development. But Ungar prefers to phrase the findings empirically: "It provides evidence of an anatomical change between Australopithecus and Homo that made our species more suited to the consumption of tough foods," he said. "When you add this to findings in the archeological record and to physiological evidence that claims our increased brain size required more efficient food sources, meat becomes the most likely explanation."

Ungar’s study is one of thirteen presentations that will be delivered Aug. 14-15 at "The Evolution of Human Diet." Leading experts on human evolution, nutrition, behavioral ecology, anthropology and medicine will deliver information aimed at educating the public about what is known and what can be known about diet and its relation to health.

Presenters range from Boyd Eaton, an expert on evolutionary medicine, to Barry Sears, author of the popular diet book, "The Zone." This broad examination of the topic is intended to provide useful information to a number of audiences, including the general public, health professionals, nutritionists and scholars. In addition, it brings together researchers from a variety of fields to share their findings, which may open opportunities for collaboration across disciplines.

"There are many researchers examining the human diet and its evolution, but they’ve taken different approaches, and they come from different professional circles. As a result, they’re often not as familiar with each other’s work as they ought to be," Ungar said. "We hope the symposium will bring about a dynamic interaction that may move the field forward."

Over the course of two days, experts each will give a 50-minute presentation, followed by 10 minutes for questions from the audience. A Web site with presenters’ biographies and abstracts is available at www.sloandietworkshop.org. A summary of the proceedings and an edited volume are expected to be published soon after the symposium.

The symposium is funded by a $40,000 grant from the Sloan Foundation under its program "The Known, Unknown and Unknowable." According to the foundation’s Web site — www.sloan.org — this program seeks "to add to the viewpoint of producers of knowledge the viewpoint of consumers" and "to explore the limits to knowledge in fields with obvious practical implications, such as health or finance, where it is important for knowledge consumers.to know what you can or cannot know."