If you are what you eat, it follows that what you eat influences how you look. But we're not talking about weight here. We're talking about appearance—specifically, the human face. Anthropologists have theorized that the human face looks the way it does today because of years of evolution dictated, in part, by the foods early humans ate. Now David Strait hopes to test this theory with help from a computer model that simulates the way primates chew.

The ability to eat very hard foods may have allowed some early humans to thrive and continue to evolve into our present-day form, Strait said. For example, later members of one extinct group, the Australopithecines, developed massive faces, gigantic teeth, and huge jawbones. One current hypothesis says the facial structure adapted to resist the stress imposed by chewing very hard foods such as nuts or seeds.

Strait, an anthropologist and assistant professor at the New York College of Osteopathic Medicine of the New York Institute of Technology, is using a computer to digitally simulate how living primates chew. He says his research may help explain why there is such diversity among today's living primates and lay the groundwork for future studies of extinct early humans.

Anthropologists computerized a macaque monkey skull to investigate early-human chewing patterns.

"Primates, including humans and their extinct relatives, are characterized by astounding diversity in diet," Strait said. "They consume a wide range of food items whose material properties vary greatly."

Changes in diet and the use of the teeth, jaws, and facial skeleton to acquire and process food have played a major role in shaping the evolutionary histories of many vertebrates, including humans, Strait said.

Anthropologists think that various aspects of the primate facial skeleton evolved from years of chewing certain types of materials and from resisting the loads imposed by chewing. Testing that theory is easier said than done, though.

The architecture of the primate face is so complex that it can't be modeled using usual biomechanical methods. As a result, few studies have been able to test which skeletal features are, in fact, chewing adaptations, Strait said. He and his team used finite element analysis software from Algor of Pittsburgh and computer-aided design software from SolidWorks of Concord, Mass., to model and analyze the facial structures, in order to test hypotheses about how they evolved from chewing methods.

Chewing presents an interesting engineering problem, Strait said. When you chew, forces are being passed up into your face and down into your lower jaw. The bite force is about the same in the upper and lower jaw.

The mandible, which is a U-shaped bone, essentially acts as a bent beam. The thin sheets of curved bone in the face don't ever become thicker in primate evolution. Instead, they change their position relative to each other. Hence, different parts of the chewing system have adapted to solve the same stress-resistance problem in different ways.

One challenge facing anthropologists is that a lot of scientific information, such as relative muscle forces and material properties of connective tissues, is unavailable for extinct species. To study how extinct humans chewed, Strait is first modeling how present-day primates chew, making sure those models are correct, and then using that information to study fossils.

"With fossils, we have information only about the shape of a bone. The muscles aren't preserved," Strait said. "Therefore, we have no direct data about the loads or constraints that should be applied to an FEA model."

As a pilot study, Strait developed an FEA model of the skull of a male macaque, a type of monkey widely used in biological and medical research. Computed tomography scans of a macaque skull from the Smithsonian Institution's National Museum of Natural History were digitized and input into the CAD model to create a three-dimensional solid model of the skull geometry.

That information may help Strait one day build an FEA model of one of the extinct early humans and make conclusions about its diet.

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