A Penn State researcher is part of the team that developed techniquesthat have generated insights into dietary divergences between some ofour human ancestors, allowing scientists to better understand theevolutionary path that led to the modern-day diets that humans consume."Our new techniques are allowing us to get beyond simple dichotomiesand helping us understand the processes by which dietary evolution isworking," said Peter Ungar, professor of anthropology at the Universityof Arkansas.
Ungar and Robert Scott, postdoctoral fellow at the University ofArkansas, with colleagues at the Worcester Polytechnic Institute, StateUniversity of New York at Stony Brook, Johns Hopkins University Schoolof Medicine and Penn State University, report their findings in theAugust 4, 2005 issue of the journal Nature.
The researchers, including Dr. Alan Walker, Evan Pugh Professor ofBiological Anthropology and Biology, Penn State, investigatedmicroscopic wear on the teeth of two species of ancient hominims --Australopithecus africanus, which lived between 3.3 and 2.3 millionyears ago, and Paranthropus robustus, which lived between 2 and 1.5million years ago. The pits and scratches found on the teeth offer avisual history of the type of food consumed by the tooth's owner. Pitsindicate a diet of hard, brittle foods, like nuts and seeds, whilescratches imply a diet of tough foods, like leaves and possibly meat.
Traditional examinations of these ancient teeth -- counting pits andlines on a black and white electron micrograph image -- suggested thatA. africanus ate tough foods and P. robustus dined on hard, brittlefare. However, the researchers used a new technique developed by Ungarand his colleagues that combines engineering software, scale-sensitivefractal analysis and a scanning confocal microscope to create areproducible texture analysis for teeth -- and the analysis tells amore complete story.
The researchers looked at both roughness, or complexity, and directionality in the teeth they examined.
"Since food objects interact with teeth, we have different kinds ofcomplexity in different diets. Directionality also correlates withdiet," Scott said. Hard foods like nuts and seeds tend to lead to morecomplex tooth profiles, while tough foods like leaves lead to morescratches, which corresponds with directionality.
The confocal microscope and engineering software allow the researchersto take three-dimensional coordinates of the entire tooth and form adetailed image of the surface. When these images are combined, they canuse fractal analysis to examine patterns in the tooth wear.The analysis showed that the two species had significant amounts ofoverlap in their diets and that while P. robustus had more complexityin its tooth wear, indicating that it ate more hard and brittle foodsthan A. africanus, it ate tough foods as well.
The researchers believe that this indicates that the species frequentlyate the same types of foods, but that in times of scarcity or seasonalchanges, P. robustus changed its diet to include foods that differedfrom those of A. africanus.
"The difference in their evolution in terms of diet is not driven bytheir preferences, but by scarcity," Ungar said. "It gives you a wholenew way of thinking about dietary adaptation."
The researchers credit the new method of examining microscopic wear onteeth with allowing them to gain new insights into dietary evolution."The old technique was subject to observer error, so we couldn't get ahandle on whether the variation we observed was real or the result ofobserver error in data acquisition," Ungar said. "The new technique isfree of subjective observer error, so the variation we see is real.This allows us to actually look at within-species variation. We canfinally get beyond 'these differed' and start to understand how muchthey differed and overlapped, and what this means in terms of theiradaptations and evolution."
"This technique does the same thing as finding new fossils," Scottsaid. The researchers examined the teeth, approached the pits andscratches with a new technique and drew new conclusions from the data."We can say things that we could never say before," he said.
The project was funded by a grant from the National Science Foundation.
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