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A paleoecological exploration probes the evolution of human diets

Evolution’s Bite: A Story of Teeth, Diet, and Human Origins

Peter S. Ungar
Princeton University Press,
2017
248 pp.
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Most popular books on human evolution leverage the discovery of a new fossil to reassess how paleoanthropologists have pieced together our evolutionary history. In Evolution’s Bite, Peter Ungar takes a very different approach, focusing on the structure and function of teeth to chart the dietary adaptations of living primates and fossil and archaeological hominin populations. Assuming that there is an element of truth in the old adage “you are what you eat,” Ungar’s perspective enjoys the dual advantages of being both novel and sound.

To carry weight in the scientific community, popular science books should be written by experts with skin in the game. Ungar certainly qualifies in this regard, having a prolific publication record that ranges from reconstructing the diets of early australopithecines to quantifying how monkeys consume different types of fruits in the tropical forests of Indonesia.

Evolution’s Bite combines personal anecdotes from Ungar’s own career with vivid historical accounts of the work of some of the pioneers in the fields of paleoanthropology, primatology, dental functional anatomy, and paleoclimatology. The resulting story, written in an easy-to-read style that often borders on being downright casual, relates how oscillating climatic regimes and annual seasonal cycles lead to constantly changing menus on Earth’s “biospheric buffet.”

PAUL NICKLEN/NATIONAL GEOGRAPHIC CREATIVE

Microscopic wear patterns on teeth and other “foodprints” can reveal the dietary preferences of ancient cultures.

To be successful in the long-term game of evolution, animals can’t afford to be picky eaters. Instead, dietary versatility is the key to success. Among modern primates, this might mean using “fallback” food options in a rainforest suffering drought conditions; for South African australopithecines, it may have meant accessing the resources available in both forests and grasslands.

Evolution’s Bite begins by introducing the basics of how teeth work. The evolution of anatomically complex or “tribosphenic” molars in early mammals enabled them to chew their food instead of simply ripping it apart, as other tetrapods do. The numerous cusps, crests, and basins that produce the complicated topography found on mammalian molars have several other important implications as well. First, upper and lower molars share complementary surfaces that enable precise dental occlusion. Second, by emphasizing either scissorlike crests or the mortar-and-pestle relationship between cusps and basins, mammalian molars can become adapted to diets requiring lots of shearing (say, insects or meat) or grinding (such as nuts).

Mammalian molars are also intricate enough that, for paleontologists, fossilized teeth function like fingerprints at a crime scene. Not only can they reveal whodunnit but often the culprit’s motive (in the form of diet) as well.

Understanding how teeth function is necessary but not sufficient to reconstruct the diets of extinct species. In part, this is because many organisms are forced to change their diets on a seasonal basis, like foodies attending a locavore farm-to-table banquet. In these cases, natural selection may have molded tooth structure to process less desirable (and rarely consumed) fallback foods rather than the staple menu items eaten throughout most of the year.

To get a better picture of what our ancestors were eating millions of years ago, Ungar makes the case for what he calls “foodprints.” Foodprints include microscopic wear patterns on teeth that result from masticating items with different physical properties, as well as the variable isotopic composition of tooth enamel, which reveals information about the food eaten by an organism as its enamel was formed.

Intriguingly, foodprints do not always yield results that are consistent with the gross morphology of the teeth on which they reside, nor even with other foodprints. For example, the isotopic foodprints of East African Australopithecus and Paranthropus indicate a divergent reliance on products of forests and grasslands, but their microwear patterns are indistinguishable. The reverse is true in South Africa, where Paranthropus and Australopithecus show different types of microwear but similar isotopes. Ungar explains these data as resulting from “an evolutionary ‘free-for-all,’ where some hominin species have different teeth and jaws for similar diets and others have similar teeth and jaws for different ones.”

Ungar concludes Evolution’s Bite by highlighting the futility of so-called “Paleolithic diets,” which aim to return us to the “natural”—and thus presumably healthier—food practices of our ancestors. Without defending contemporary Western diets that include too much sugar and refined carbohydrates, Ungar makes a compelling case that any diet intended to promote weight loss is inconsistent over the long run with the basic premises of natural selection. Moreover, given the constantly changing menu on the biospheric buffet, Ungar questions which Paleolithic ancestor it is that we’re trying to emulate.

About the author

The reviewer is at the Department of Ecology and Evolutionary Biology, The University of Kansas, Lawrence, KS 66045, USA.