What teeth can teach about how mankind developed

A leading paleoanthropologist from Arkansas describes in his new book what can be learned from the ‘living fossils’ in our mouths. Judy Siegel-Itzkovich reports

If we are what we eat, then it is not only because of what food passes through the digestive system but also how the teeth nibble, gnaw, chew, crunch, munch and scrunch on what food is available. In fact, according to leading American paleoanthropologist Prof. Peter S. Ungar, we carry in our mouths the “legacy of our evolution,” as “our teeth are like living fossils that can be studied and compared to those of our ancestors to teach us how we became human.”

He has written a challenging and fascinating book called Evolution’s Bite: A Story of Teeth, Diet, and Human Origins. The $28, 236page, hardcover volume, published by the Princeton University Press and distributed by John Wiley and Sons Ltd., will interest not just dentists, but anthropologists and laymen interested in understanding human evolution, climate change, the move from hunting and gathering to agriculture and the role in which the shape, chemistry and use of teeth influenced the development of man.

In fact, he has dedicated his career to the study of the evolution of teeth. With three decades of experience traveling around the world to observe animals and view fossils and conducting research in his lab, Ungar displays much wisdom, humor and cutting-edge scientific knowledge.

Living in Fayetteville, Arkansas, Ungar is distinguished professor and director of the Environmental Dynamics Program at the University of Arkansas. Before arriving in that state, Arkansas, he taught at the Johns Hopkins School of Medicine in Baltimore and the Duke University Medical Center in North Carolina.

He previously wrote Teeth: A Very Short Introduction, and Mammal Teeth: Origin, Evolution, and Diversity. He was also editor of Evolution of the Human Diet: The Known, the Unknown, and the Unknowable and author or co-author of more than 150 published scientific papers. He has also appeared in documentaries on the Discovery Channel, BBC Television and the Science Channel.

According to the publisher, he has spent thousands of hours observing wild apes and other primates in the rain forests of Latin America and Southeast Asia, studied fossils from tyrannosaurids to Neanderthals and developed new techniques for using advanced surface analysis technologies to divulge information about diet from tooth shape and patterns of use wear. USUALLY WITH utmost seriousness but also with wit, humor and sometimes tongue-in-check, the author has coined the word “foodprints” to describe unique patterns of scratches and wear on teeth. These belong to hominids (extinct and modern great apes) and hominins (modern and extinct human species and all our immediate ancestors. From these marks and a lot of scientific detective work, the 54-year-old Ungar did a lot of legwork, sinking his teeth into the analysis of various species. He learned what they ate out of choice or the lack of it due to changes in the climate and migration. All this varied the food options that were available to the hungry creatures, who fed over the eons at what he calls the “biospheric buffet.”

He also extensively cites scientists who made discoveries in various disciplines before him, providing nearly 200 notes over 20 pages.

The cusps, crests and basins that form the surface of the teeth – incisors, cuspids, bicuspids and molars – each have different structure and functions in the tearing, chewing and grinding of food.

He once asked his daughters when they were only five and seven and visited the Museum of Discovery in Little Rock about a skulls of a lion and of a giraffe. He asked which one ate meat. The carnivorous lion did, they noted, because the skull had sharp, blade-like teeth, while the herbivorous giraffe had broad, flat molars for grinding leaves.

However, he continues, what about more subtle differences such as between animals that eat different parts of animals and of plants and for what foods are human teeth designed?

Fortunately for Ungar and for science, tooth enamel is the hardest substance in the body – even more resilient than bones and last for much longer, He looks back at the early diets of australopithecines and observes how monkeys in the tropical forests Indonesia chewed different varieties of fruit then and now.

“Other species don’t have crooked, crowded and impacted teeth riddled with holes. Why do we? It is clear that, while our ancestors ate different foods at different times and in different places, there is a genuine mismatch between our diets and our teeth,” he notes. “If we consider them in this light, they remind us of our evolution. Our teeth connect us to our ancestors.” HOW TEETH wear down with use is also interesting. Rabbits, for example, chomp on vegetables so much that their teeth wear down quickly and grow longer endlessly. They don’t have to go to the dentist.

“I’ve argued that nature uses wear as a sculptor would use a chisel to refine and enhance teeth and keep them in as good working order as possible. Our genes should make teeth predestined to wear down in a specific way, adopted to a specific abrasive environment and diet. “In fact,” Ungar continues, “some species actually need their teeth to be worn for them to work. Many rodents begin to grind their teeth in the uterus because their molars need to be worn and ready to go shortly after birth. They depend on wear to provide the sharpened, jagged surfaces used to grind tough vegetation.”

Matching tooth forms in hominins and foodprints “can help us understand what individuals in the past ate, but not necessarily why they ate it. That’s where concepts from evolutionary theory come in. We’ve learned that specialized teeth can reflect a specialized diet or a more generalized one. This is because natural selection seems to focus more on foods that pose the greatest challenge and less on their proportion in

the diet. We’ve learned that teeth can evolve for new foods or for more of the same if a change in the crown shape increases the efficiency with which they fracture whatever it is they have to break.”

The length of one’s jaws is not determined only by species or genetics, but also by the stress put on it while chewing and one’s diet, which determines how well jaw length matches tooth size.

Moving on to humans, Ungar notes that we “walk on two legs and carry tools, food and other things from place to place. We communicate with language to broker social relationships and exchange information about the past and future. We share and grade food as part of our ‘corporate responsibility.’ We… maintain a home base, or central place, where we bring and divvy up the bounty collected while hunting and gathering. We share meals. Other primates don’t even have meals. They tend to eat food when and where they find it, and at most tolerate some scrounging.”

Getting food was mostly gender-based. Males hunted and women gathered, but hunting creatures to eat meat received the most importance. Mothers bore and fed their babies for more than 200 million years, he writes, and needed males to hunt. This paved the way for the human nuclear family.

As males provided for their nutritional needs, the women cared for their offspring, thus lengthening the time children were dependent on their parents. Grandmothers, suggest some researchers, who can no longer bear children, also provide for the young, gathering fruit to help out their own offspring. But most wild fruits are tough and dry, fibrous and bitter – not easy on teeth. Cooking developed to make them more palatable and easy to digest.

The Neolithic Revolution, he continues, came along and was not, as many believe, resulting from climate change. “It was about a change in the way people viewed their place in nature. People started to think of themselves as apart from nature rather than part of it.” UNGAR EVEN enters our own neighborhood in the Middle East. He cites the Sea of Galilee (our Kinneret), whose depth fluctuates with the annual rains. When rainwater was scarce, an amateur archeologist discovered some animal bones, flint objects and a human jaw on the beach south of Tiberias. Two sites that were investigated were called Ohalo I and Ohalo II. People from the Israel Antiquities Authority uncovered “hundreds of thousands of plant parts and bone fragments. The preservation was incredible – the best ever for a site of its age. Ohalo II gives us an unprecedented snapshot of life in the Levant before the Neolithic Revolution” some 23,000 years ago, Ungar writes.

The remains included wild almonds, pistachios, olives, grapes and many other plant foods, along with plenty of bones from fish, gazelles, deer, hares and other wild animals. There was also a grinding stone for wild barley, wheat and oats. “People settled there as resources allowed. They gathered and maybe even grew cereals.” The shift from foraging to farming changed the human body and mouth as well.

The more recent growing of corn led to cavities and periodontal disease, Ungar reports. The author makes fun several times of the so-called “Paleo weight loss diet” that some of our contemporaries around the world are observing and eating – with a lot of meat and vegetables, nuts, eggs, seeds and fish and avoiding cereal grains, legumes, dairy products and potatoes – as if we were cavemen. He notes that “we cannot return to nature and lose weight, as this works against natural selection.”

A lot of work “remains for us to understand the details of why teeth have shrunk as they have over the past few thousand years, but it’s clear that the Neolithic Revolution had something to do with it.”

Finally, the author goes into what the “natural human diet” is, a question still debated today among carnivores, vegetarians and vegans.

“Are we intended to eat meat, or are we innately vegetarian? From our vantage point, there doesn’t seem to be an answer, because the question itself is built on a fundamental misunderstanding of the evolution of human diet. Still, that doesn’t mean we can’t benefit from asking it.”

Because table sugar or sucrose became widely available only after the Industrial Revolution, just a dozen generations from us, not enough time has passed “for us to evolve a way to keep it from rotting our teeth… We may be struck with an oral environment our ancestors never had to contend with,” he concludes, “but recognizing this an help you deal with it in better ways. Think about that the next time you smile and look in a mirror.”

The Arkansas scholar definitely gives his readers plenty of food for thought.