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Human evolution
Ancient teeth tell diet secrets

Fossilized teeth have revealed that millions of years before supermarkets hit the scene, our ancestors still managed to have varied diets. Now, a new analysis shows that the variation was subtle and was driven by resource scarcity, not preference.

Examining a species’ teeth under a microscope can reveal what the animal typically ate; a pitted surface implies a diet of hard and brittle foods such as nuts and seeds, while uniform scratches imply a diet of tough foods such as leaves and stems. Previous measurements of the etchings, so-called microwear, on the teeth of hominids from 3 to 1 million years ago were made by hand, and determined that Paranthropus robustus ate hard foods and Australopithecus africanus ate tougher foods.

“The problem was that we just didn’t know whether the variation we saw was just because of observer error or whether it was real,” says Peter Ungar, an anthropologist at the University of Arkansas. So, Ungar and colleagues developed a computer program to automatically map and measure the microwear. “Basically we get a topographic map, a digital map of the [tooth] surface in 3-D,” Ungar says. Their results, published in the Aug. 4 Nature, suggest that for the most part, the diets of the two early hominids overlapped.

Slight differences between the two species, however, confirmed previous findings that P. robustus teeth were more pitted from hard foods. “I am not really surprised by the results,” says Fred Smith, an anthropologist at Loyola University in Chicago. “The earlier ideas that A. africanus and P. robustus were distinguished by strikingly different diets have been falling out of favor for many years.”

Ungar thinks that the slight dietary differences were driven not by preference, but by a changing environment and resource scarcity. A. africanus lived between 3 and 2 million years ago when forests dominated Africa, Ungar says, but when P. robustus arrived about 1 million years later, the continent had begun to dry out.

When possible, both ate mostly soft sugary fruits, Ungar says, “but when push came to shove, I would say that P. robustus probably had to fall back on the resources available to it in the dry savannah that had spread throughout southern Africa at that point.” He notes that harder foods like roots, tubers, nuts and seeds would likely be found in the drier, more open environments. “And we see that in the microwear.”

The next step will be to use the technology to look at teeth from the earliest known members of our own genus, Ungar says. “The goal is to put together a story of the evolution of human diet.”

Kathryn Hansen

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