WPI Researchers Use Space Age Technology to Help Understand Stone Age Diets

Science Journal Nature Reports Findings in August 4 Issue

Contact: WPI Media Relations, +1-508-831-5609

WORCESTER, Mass. -- August 4, 2005 -- What did our early ancestors eat? A Worcester Polytechnic Institute research team is helping anthropologists and paleoanthropologists better answer that question using new measurement techniques based upon ongoing WPI Surface Metrology Laboratory research, which has also been applied to Space Shuttle runways, manufacturing processes, and even potato chips and chocolate. The techniques are the result of a National Science Foundation-funded project to use three-dimensional topographical measurements to study dental microwear -- one of the most commonly used approaches for reconstructing the diets of early hominins and other fossil primates.

WPI mechanical engineering professor Christopher A. Brown and Torbjorn S. Bergstrom '95, associate director of the Surface Metrology Laboratory, along with colleagues at the University of Arkansas, State University of New York at Stony Brook, Johns Hopkins University School of Medicine, and Penn State University, report their findings in the August 4, 2005, issue of the science journal Nature.

Brown and Bergstrom's research partners were looking for an objective way to examine microscopic wear on teeth. For example, in the study published in Nature, they looked at dental microwear of two species of ancient hominins -- Australopithecus africanus, which lived between 3.3 and 2.3 million years ago, and Paranthropus robustus, which lived between 2 and 1.5 million years ago. The microscopic pits and scratches found on the teeth offer a visual history of the type of food consumed by the tooth's owner. Pits indicate a diet of hard, brittle foods, like nuts and seeds, while scratches imply a diet of tough foods, like leaves and possibly meat.

The problem was that traditional examinations of these ancient teeth were subjective. They were done using optical and scanning electron microscope (SEM) imaging, and manual image analysis -- requiring researchers to personally count pits and lines on black and white images. Therefore, analysis of the same image could vary between researchers.

The new technique developed by Brown, Bergstrom and their colleagues is a much more quantifiable approach using 3-D topographical measurements. First, the dental surfaces are measured with a white-light confocal microscope, an innovative technology that produces high-resolution images comparable to those of the SEM at the scales of interest, but that also generates 3-D topographic maps of the dental surfaces.

Then, the maps are quantitatively analyzed using variations of scale-sensitive fractal analysis (SSFA) software algorithms that Brown and Bergstrom originally developed for applications in manufacturing, materials, and mechanical engineering. The SSFA software analyzes the 3-D measurements made by the confocal microscope and recognizes the microgeometry, or texture, of the surface fractal characteristics. The algorithm characterizes the complex surfaces left from the ancient microwear by calculating how the apparent area changes with the scale of observation. The WPI software alleviates researchers' dependence on the human eye for analysis, thus yielding accurate, repeatable information about the marks.

The new analysis showed that the two species studied in the Nature article had significant amounts of overlap in their diets, and that while P. robustus had more complexity in its tooth wear, indicating that it ate more hard and brittle foods than A. africanus, it ate tough foods as well. The researchers believe that this indicates that the species frequently ate the same types of foods, but that in times of scarcity or seasonal changes, P. robustus changed its diet to include foods that differed from those of A. africanus. Previously, traditional examinations of these ancient teeth suggested that A. africanus ate tough foods and P. robustus dined on hard, brittle fare.

The anthropologists on the research team credit the new method of examining microscopic wear on teeth with allowing them to gain new insights into dietary evolution.

"The old technique was subject to observer error, so we couldn't get a handle on whether the variation we observed was real or the result of observer error in data acquisition," notes Peter S. Ungar, professor of anthropology at the University of Arkansas. "The new technique is free of subjective observer error, so the variation we see is real. We can finally get beyond ‘these differed' and start to understand how much they differed and overlapped, and what this means in terms of their adaptations and evolution."

In scientific terms, the measurement and analysis of such topography, in this case dental microwear, is known as surface metrology -- the study of how surface texture (i.e., topography, or roughness) influences behavior and how surface texture is influenced by wear, fracture, growth, disease, corrosion, and manufacturing processes. The WPI Surface Metrology Lab is the only academic laboratory in the U.S. dedicated to the field, and it has been a significant source of innovations and discovery. It pioneered the development and application of scale-sensitive fractal analyses, a method invented and patented by Brown and his co-workers.

"I have been working with my students on this kind of scale-sensitive fractal analysis over the last 20 years in Switzerland and at WPI for industrial applications," says Brown. "But in that time we have found no shortage of other applications to apply the method to -- from Space Shuttle runways and cutting tools, to potato chips and chocolate; and now pre-historic teeth."

The software that Brown, Bergstrom, and their research partners developed to analyze dental microwear is available as part of a beta test release. Called Toothfrax Microwear Texture Analysis (3D), it allows analysis of 3-D surface data using scale-sensitive fractal analysis and generates measurements of surface complexity and anisotropy. For information and inquiries about beta testing Toothfrax, visit Brown and Bergstrom's software and surface analysis services Web site, Surfract.