Review: May 2017

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The fossil jaws of prehistoric hominins have stories to tell, and they speak most eloquently to such paleoanthropologists as University of Arkansas professor Peter Ungar. What did our ancestors eat? Did they gather food or cultivate crops? What diseases did they suffer from? The answers are found in their teeth, if one knows where to look. 

Some clues are obvious, even to the untrained eye—our ancestors evolved to eat a wide variety of foods: we bear both the sharp bladed teeth of dogs and lions and the flat molars of cows and hippos. While natural selection favors adaptations that help organisms find edible food in challenging times, an animal’s daily diet depends primarily on what foods are available on a typical day.

To narrow down what our ancestors ate, rather than what they could have eaten, Ungar looks to what he calls “foodprints,” subtle traces of wear or chemical alteration that show up using modern analytical tools. Under the high magnification of a scanning electron microscope, fossil teeth reveal a spectrum of pits and scratches, whose texture and complexity can be compared to similar scans of living creatures. It’s interesting that these close looks often belie first impressions: the teeth of Parantropus boisei, an eastern African hominin whose wide, flat teeth and massive jaw muscles earned it the nickname “nutcracker,” showed smooth surfaces more typical of fruit-eating monkeys, rather than the heavily scarred surfaces produced by grinding hard seed. “If the nutcracker cracked nuts, there was no sign of it in the microwear,” Ungar observes.

Chemical foodprints allow even finer distinctions to be drawn. The ratio of heavy-to-light carbon isotopes in teeth depends on whether a person’s diet included such seed grasses as maize, or whether it relied more heavily on fruits or root vegetables. These indexes, in turn, provide evidence for shifts from foraging to agriculture, and even for the emergence of cooking (which softens food and reduces tooth wear for a given type of diet chemistry).

Despite the highly technical character of paleontological research, the subject of ancient diets is one of great popular interest today, driven in part by current, widespread thinking that we are what we eat. Yet, readers looking for the proper diet—a “paleo,” or “natural,” match to our biology—will be disappointed. The “biospheric buffet” of every age and every locale is different, which is what the research shows. Nature’s menu, like that of a high-end restaurant, reflects what’s available on a given day in forest, field, and farm. Modern civilization has given us more choices, which have no doubt led to problems of excess, but it has also provided us with the leisure and resources to explore our past, as Ungar and his colleagues are doing so well, and to make informed choices about where we go from here.