Ancient 'Nutcracker Man' Challenges Ideas on Evolution of Human Diet

New evidence shows that our ancient human ancestors did not feed regularly on hard or tough foods.

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Scientists called him "Nutcracker Man" because the ancient hominin that lived around 2 million years ago had the biggest, flattest cheek teeth and the thickest enamel of any known human ancestor. And so, figured scientists, the species known as Paranthropus boisei probably fed on nuts and seeds or roots and tubers because his teeth, cranium and mandible appear to be built for chewing and crunching hard objects.

But according to new evidence, "It looks more like they were eating Jell-O," said Peter Ungar, professor of anthropology at the University of Arkansas in Fayetteville, who led a recent study suggesting that none of the P. boisei individuals he examined ate extremely hard or tough foods in the days leading up to death.

"These findings totally run counter to what people have been saying for the last half a century," said Ungar. "We have to sit back and re-evaluate what we once thought."

Anthropologists have traditionally inferred the diet of ancient human ancestors by looking at the size and shape of the teeth and jaws. But by using powerful microscopes to look at the patterns of wear on a tooth, scientists can get direct evidence of what the species actually ate. Since food interacts with teeth, it leaves behind telltale signs that can be measured. Hard foods like nuts and seeds, for instance, lead to more complex tooth profiles, while tough foods like leaves lead to more parallel scratches.

Ungar and his colleagues, Frederick E. Grine of State University of New York at Stony Brook and Mark F. Teaford of Johns Hopkins University, Baltimore, Md., compared dental microwear profiles of P. boisei to modern-day primates that eat different types of foods. P. boisei teeth were compared to those of Old World monkeys living in Asia, the Middle East, Africa and Gibraltar, as well as those of New World monkeys living in tropical forests in southern Mexico and Central and South America.

The researchers also compared the teeth to some of P. boisei's more contemporary counterparts—Australopithecus africanus, which lived between 3.3 million and 2.3 million years ago, and Paranthropus robustus, which lived between 2 million and 1.5 million years ago.

The light wear pattern was more consistent with modern-day fruit-eating animals than with most modern-day primates and may suggest evolutionary adaptation for eating may have been based on scarcity rather than on an animal's regular diet. But Ungar points out that the teeth only suggest "what P. boisei could eat, not necessarily what it did eat." In fact, research has shown that animals may actively avoid eating the very foods they have developed adaptations for when they can find other food sources.

"This challenges the fundamental assumptions of why such specializations occur in nature," Ungar said. "It shows that animals can develop an extreme degree of specialization without the specialized object becoming a preferred resource."

Accordingly, the finding represents a fundamental shift in the way researchers look at the diets of early human ancestors and what role specific food sources may have played in extinctions.

The team reported their findings last week in the online journal Public Library of Science One. The research was funded in part by the National Science Foundation.

—Bobbie Mixon/NSF

This report is provided by the National Science Foundation, an independent federal agency that supports fundamental research and education across all fields of science and engineering, in partnership with U.S. News and World Report.