A recent study by anthropologist Peter Ungar of the University of Arkansas and colleagues has challenged the conventional way that anthropologists determine what early human ancestors ate. Apparently, they didn't necessarily eat what they "should have."

The size and shape of teeth and jaws have usually been assumed to determine eating habits. Thus, most researchers assumed that "Nutcracker Man" (Paranthropus boisei), flourishing between 2.3 and 1.2 million years ago, would thrive on nuts, seeds, and possibly fleshy roots. That made sense because, as ScienceDaily notes , "'Nutcracker Man' had the biggest, flattest cheek teeth and the thickest enamel of any known human ancestor."

However, Ungar's team took a different approach to the eating habits of this hominin (life form believed to be a human or human ancestor): They decided to look at microscopic wear patterns on the teeth of seven specimens whose teeth were well enough preserved for the purpose. They were found in Kenya, Ethopia, and Tanzania over a million year spread.

The researchers argued that actual wear patterns are a more reliable guide to diet than tooth structure. As they explained,

... craniodental functional morphology [shape of jaw and teeth] offers insights into what a hominin could have eaten, but not necessarily what it actually ate on a regular basis. By contrast, dental microwear, the pattern of microscopic use-wear on a tooth, is caused by, and reflects, specific foods eaten by the individual whose teeth are being examined. Thus, microwear can provide direct evidence for the diets and foraging strategies of fossil species. [from the study]

So what did Paranthropus boisei eat on a regular basis? The light wear that the micro analysis showed was consistent with a usual diet of soft food rather than hard or tough food. "It looks more like they were eating Jell-o", Ungar told ScienceDaily. He was also quite straightforward about the fact that his team's findings are contrary to conventional assumptions:

"These findings totally run counter to what people have been saying for the last half a century," said Peter Ungar, professor of anthropology in the J. William Fulbright College of Arts and Sciences. "We have to sit back and re-evaluate what we once thought."

Ungar believes that the findings might be explained by Liem's Paradox, sometimes observed in fish, which states that

... specialized morphology can allow for a broader diet wherein a species may actively avoid the very foods to which it is adapted when other, more preferred resources are available. (from the study)

As he told Jennifer Bryner at LiveScience

"If you give a gorilla a choice of eating fruit or a leaf, it will take the fruit every time," Ungar said. "But if you look at a gorilla's skull, its sharp teeth are adapted to consuming tough leaves. They don't eat the leaves unless they have to."

Whether or not Liem's Paradox explains Nutcracker Man's preference for soft, squishy food, this study implies that tooth shape cannot really tell us much about what ancient humans usually ate.

That, in turn,  casts doubt on a theory about why Paranthropus boisei went extinct. While some have believed that these hominins went extinct because they could not adapt to the climate change that took away their specialized diet, the new findings show that they could eat pretty much the range of food that modern humans can.

See also: University of Arkansas (2008, April 30). New Findings Challenge Conventional Ideas On Evolution Of Human Diet, Natural Selection. ScienceDaily. Retrieved May 6, 2008, from http://www.sciencedaily.com? /releases/2008/04/080429204255.htm Note: This article may be downloaded free here.

Abstract: The Plio-Pleistocene hominin Paranthropus boisei had enormous, flat, thickly enameled cheek teeth, a robust cranium and mandible, and inferred massive, powerful chewing muscles. This specialized morphology, which earned P. boisei the nickname “Nutcracker Man”, suggests that this hominin could have consumed very mechanically challenging foods. It has been recently argued, however, that specialized hominin morphology may indicate adaptations for the consumption of occasional fallback foods rather than preferred resources. Dental microwear offers a potential means by which to test this hypothesis in that it reflects actual use rather than genetic adaptation. High microwear surface texture complexity and anisotropy in extant primates can be associated with the consumption of exceptionally hard and tough foods respectively. Here we present the first quantitative analysis of dental microwear for P. boisei. Seven specimens examined preserved unobscured antemortem molar microwear. These all show relatively low complexity and anisotropy values. This suggests that none of the individuals consumed especially hard or tough foods in the days before they died. The apparent discrepancy between microwear and functional anatomy is consistent with the idea that P. boisei presents a hominin example of Liem's Paradox, wherein a highly derived morphology need not reflect a specialized diet.

Citation: Ungar PS, Grine FE, Teaford MF (2008) Dental Microwear and Diet of the Plio-Pleistocene Hominin Paranthropus boisei. PLoS ONE 3(4): e2044. doi:10.1371/journal.pone.0002044 Editor: Michael Petraglia, University of Cambridge, United Kingdom Received: January 25, 2008; Accepted: March 12, 2008; Published: April 30, 2008