Ample evidence abounds in support of Lieberman’s observations. A comparison of 146 medieval skulls from abandoned Norwegian graveyards with modern skulls indicated a trend toward bad bite in our more recent forebears. The skulls of people scored as being in “great” or “obvious” need of orthodontic treatment made up 36 percent of the medieval sample and 65 percent of the modern sample. And evidence of malocclusion in still earlier human fossils is vanishingly rare. The jaws of hunter-gatherers nearly uniformly reveal roomy, perfect arches of well aligned teeth, with no impacted wisdom teeth—a movie star’s dream smile, 15,000 years before the movies!

The museum I work in has thousands of ancient skulls from all over the world. Most of the skulls from the last few hundred years are a dentist’s nightmare: they are filled with cavities and infections, the teeth are crowded into the jaw, and about one-quarter of them have impacted teeth. The skulls of preindustrial farmers are also riddled with cavities and painful-looking abscesses, but less than 5 percent of them have impacted wisdom teeth. In contrast, most of the hunter-gatherers had nearly perfect dental health. Apparently, orthodontists and dentists were rarely necessary in the Stone Age.

As it turns out, our ancestors did not suffer from crooked teeth to the same extent that we do today. Our species’ fossil record reveals a telling story: the epidemic of crooked teeth developed in humans over time. Evolutionary biologist, Daniel Lieberman, notes the pattern in his book, The Story of the Human Body :

Modern industrialized societies are plagued by crowded, ill-aligned teeth, a condition that the dental profession refers to as “malocclusion”—which translates literally to “bad bite.” Survey data from 1998 suggests that as much as a fifth of the U.S. population has significant malocclusion, over half of which require at least some degree of orthodontic intervention. Braces, tooth extractions, and retainers are the bread and butter for all the dentists and orthodontists tasked with setting straight our dental deviations. Having braces as a child has become so common in the Western world that it can seem a rite of passage—today, an estimated 50 to 70 percent of U.S. children will wear braces before adulthood. But what did humans do to fix their teeth before modern dentistry, before Novocain, gauze, and rubber spacers?

Our ancestors did not suffer from crooked teeth to the same extent that we do today.



So what’s happening to our mouths? Why do we today face an epidemic of crowded, unruly, crooked teeth? The answer, as it turns out, has been lying right under our noses the whole time: the problem is our jaws.

A key precipitating factor for malocclusion relates to the size of our jaws. For healthy development, jaws must be able to provide sufficient room for all of the thirty-two teeth that grow in the mouth. Over time, our teeth have grown crooked because our jaws have grown smaller. Why? The epidemic’s roots lie in cultural shifts in important daily actions we seldom think about; things like chewing, breathing, or the position of our jaws at rest, and these changes have in turn been brought about by much bigger sociohistorical developments—namely, industrialization.

Our upper jaw, which is technically known as our maxilla, seems as if it is just the base of our skull, but it is actually formed by two bones, one on each side, fused together. Our lower jaw, technically the mandible, is likewise made by the fusion of two bones. If the jaws develop correctly they have ample room for all of the teeth, and the teeth fit together well. Both upper and lower jaws can move and change in the process of development. But that process has been gradually altered ever since our ancestors began to use tools, cook, cease their mobile hunting-gathering lives and settled down to practice agriculture some 10,000 years ago.

Anthropologists have reported that the size of the human mouth has long been shrinking. Because human beings have been using stone tools for at least 3.3 million ears, that may represent the time during which the shrinkage has occurred. Stone tools permitted a greater shift to a carnivorous diet because the ability to cut meat into small pieces reduced the amount of chewing required to extract nourishment. Less chewing reduced the need for large, powerful jaws. The advent of agriculture accelerated this trend. As anthropologist Clark Larsen noted, “There has been a dramatic reduction in the size of the face and jaws wherever humans have made the transition from foraging to farming.” The superficial result, as we have seen, is malocclusion.

Jaws » presents the biological, dietary, and cultural changes that have driven us toward a major, modern health challenge.

At its root, the problem we face is that we have entered a space age world with Stone Age genes—genes that evolved to produce jaws adapted to a hunter-gatherer diet. Today’s jaws epidemic is concealed behind the commonplace. Its most obvious symptoms are oral and facial: crooked teeth (and the accompanying very common use of braces), receding jaws, a smile that shows lots of gums, mouth breathing, and interrupted breathing during sleep. A bother, but hardly an “epidemic”—at least until one recognizes the relationship between malocclusion and a veritable host of downstream health consequences.

If the jaws fail to develop properly, the receding lower jaw (the mandible) can put stress on the airway. The problems associated with modern jaw-face-airway development are only now beginning to be uncovered, largely through the work of a series of dedicated scientists and practitioners who have observed dramatic changes in facial structure that correlate with higher incidence of chronic diseases. Reducing the size of the airway can, for instance, eventually lead to breathing problems, such as sleep apnea, which itself has become a significant factor in public health. Some 20 percent of American adults are afflicted, and about 3 percent have a sufficiently serious case to cause daytime sleepiness. But sleepiness is the least of it: As many as half of all cardiac patients suffer from the disease. Sleep apnea also appears to generate mental problems, including lowered IQ, shortened attention span, and difficulties with memory.

That the diseases just noted are related to modern civilization is strongly indicated by the near absence of their symptoms in the evolutionary and historical records. Our hunter-gatherer ancestors had spacious jaws, with a continuous smoothly curved arch of teeth in each jaw, including third molars (“wisdom teeth”) at the back ends of the arches. Today, the failure of these last molars to erupt—for our wisdom teeth to emerge healthfully from the gum—has become an all too common phenomenon that often leads to dental extraction and the attendant burdens of pain, swelling, bruising, infection, and general discomfort. But with proper attention to diet, eating habits, breathing patterns, and overall oral posture (how we hold our jaws together at rest), many aspects of this epidemic, like molar impaction, could be ameliorated or avoided entirely. Jaws could return to their hunter-gatherer patterns of growth.

The bottom line is that our health and happiness (and that of our children) may be at risk due to habits which most of us never give a second thought. But how we eat can be just as important as what we eat; how we breathe can be just as important as what’s in the air we breathe; how we sleep can be just as important as how long we sleep. These are all key aspects of the jaws epidemic and part-and-parcel of overall oral-facial health. It is often said that the face is the window to the soul, but it is also a window on the health status of the person behind the face. Gummy smiles, crooked teeth, agape mouths are all visible signals that belie potentially much more serious underlying health problems. To address these problems our focus has to be on the healthy development of our jaws.

This post has been adapted from Jaws: The Story of a Hidden Epidemic by Sandra Kahn and Paul R. Ehrlich.

Start reading Jaws »



Dr. Sandra Kahn, D.D.S., M.S.D., has twenty-five years of clinical experience in orthodontics and is part of craniofacial anomalies teams at the University of California, San Francisco and Stanford University. She practices pediatric sleep apnea prevention and whole-body treatment, lectures internationally, and is co-author of Jaws: The Story of a Hidden Epidemic.

Paul R. Ehrlich is the Bing Professor of Population Studies Emeritus and President of the Center for Conservation Biology at Stanford University. He is a member of a National Academy of Sciences and the recipient of numerous international honors in the field of science. He is author to several books, including the 1968 bestseller, The Population Bomb, and co-author of Jaws: The Story of a Hidden Epidemic.