Wild Thing: Human Teeth vs. Other Mammalian Teeth

Wild Thing is an occasional series where JHU Press authors write about the flora and fauna of the natural world—from the rarest flower to the most magnificent beast.

Guest post by Peter S. Ungar

Open your mouth and look in a mirror. Millions of us suffer fillings, crowns, wisdom tooth extractions, and braces each year. Most other mammals don’t have widespread dental disease and orthodontic disorders. Why are we so different? The answer is rooted in our evolutionary history. In effect, our diet is changing too fast for our teeth and jaws to keep up. It’s natural selection in action, at least for those unlucky enough to lack proper oral care or access to dental practitioners.

When plaque bacteria break down carbohydrates, they produce acid. This leads to dental caries, or progressive decay of enamel and dentin. While about 90% of young adults in the US develop caries, only a handful of human ancestor teeth have them. Few early modern human foragers did either, less than 2% by some estimates. And rates of caries are also low in peoples that hunt and gather wild foods for a living today.

Carbohydrate consumption surged with the domestication of cereal grains and spread of agriculture, causing the caries rate to increase something like fivefold. That rate skyrocketed in the 19th and 20th centuries with widespread availability of processed sugars and sugar-rich foods because plaque bacteria break down sugar much more rapidly than other carbohydrates. This means more acid is produced, and more rapid tooth decay occurs. There are certainly other factors to consider—genetic propensity, developmental defects, pathological saliva—but diet change was key.

What about orthodontic disorders? Crowded, crooked, misaligned, and impacted teeth are huge problems today. Nine in ten of us have at least slight malocclusion, and half could benefit from orthodontic treatment. Orthodontic disorders were also much less common in fossil human ancestors and early peoples than today. And the change can come as quickly as one generation; dental anthropologists see it in the children of traditional foragers when they adopt a westernized diet.

The problem is a mismatch between jaw length and tooth size. This has led to dental crowding at both ends of the jaw. Many of us don’t have enough room for back teeth. Wisdom tooth impaction occurs ten times more often in our society than among traditional hunter-gatherers. Our lower front teeth tend to be crooked and crowded together, and our uppers are pushed forward. Recent foragers and our distant ancestors more often had an edge-to-edge bite between opposing incisors rather than tips of the uppers resting in front of the lowers—thought by most clinicians to be normal occlusion.

Why the mismatch between jaw and teeth? It looks like our jaws are too small. And indeed, human jaws have become shorter since the Early Stone Age. Researchers believe they are underdeveloped because soft, highly processed foods don’t provide the strain from heavy chewing needed to stimulate normal jaw growth during childhood. How much could we save in orthodontics bills if only our children ate more jerky?

Our teeth are a constant reminder that evolutionary history has much to teach us. Smile and think about it the next time you see a mirror.

Peter S. Ungar is Distinguished Professor and chair of anthropology at the University of Arkansas and author of Mammal Teeth: Origin, Evolution, and Diversity, available from the JHU Press.

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