Why Wisdom Teeth Are So Much Trouble

… and other evolutionary questions for an anthropologist who studies ancient teeth.

A male Barbary Macaque shows its teeth. (Rafael Marchante / Reuters )

Given all the fuss modern humans are told to put into our teeth—brush, floss, drink fluoridated water, go to the dentist to get tartar scraped off twice a year—I’ve wondered how our ancestors made do. What did their teeth look like?

Peter S. Ungar’s new book, Evolution’s Bite: A Story of Teeth, Diet, and Human Origins, is a deep dive into how the teeth of our ancestors have changed over time. Ungar is an anthropologist who specializes in teeth. With patience and the right expertise, ancient molars can help reveal the diets of our ancestors. “Teeth,” Ungar writes, “are ready made fossils.”

The book also doubles as a recounting of his career, which has run the gamut from watching monkeys in the Indonesian rainforest to repurposing mapping software for the topology of ancient teeth.

I called Ungar at his office at the University of Arkansas, and we spoke about how human teeth got to where they are today. A condensed and lightly edited transcript of our conversation is below.

Sarah Zhang: I’d like to begin with where your book ends, which is the modern scourge of impacted wisdom teeth. Our ancestors had wisdom teeth, they did not have dentists, and they did not have so many problems. Aside from possibly being over-diagnosed, why are impacted wisdom teeth a uniquely modern problem?

Peter Ungar: It’s a uniquely modern problem because we don’t grow our jaws long enough to accommodate our teeth. It turns out that nature has selected our jaw length on the basis of what it expects us to be doing during the period of time the jaw is growing. The more frequently you put force on the jaw, the longer the jaw grows. Nature has to guesstimate how long your jaw should be for teeth of a given size. Today we don't achieve that because we’re eating mush as kids.

Zhang: Does that mean we’re going to see Paleo diets where you chew on tough grass, or Paleo jaw workouts?

Princeton University Press

Ungar: You know it’s funny you say that because there are orthodontists that are starting to use treatments that actually lengthen the jaw. The traditional treatment is to shave down or take out teeth to fit everything in properly.  And now there are orthodontists that are starting to put spacers to lengthen your jaw. They’re taking a lesson from what you might call evolutionary dentistry.

Zhang: What about cavities? You sometimes hear that the invention of agriculture is tied to a big increased in cavities.

Ungar: The conventional wisdom in bioarchaeology is that the onset of agriculture and the increase in carbohydrate consumption led to more cavities. These carbohydrates—and especially later on when we hit the Industrial Revolution and the wide availability of refined sugars—provide a bed to which the bacteria that cause cavities can stick. They provide food for the bacteria as well. These microorganisms they eat, then they reproduce, and they poop. And it’s that poop basically that is acidic and erodes the teeth and causes cavities.

There’s certainly some evidence in a lot of the world where that’s the case, particularly the New World where people started to consume a lot of maize, a lot of corn. The cavities rate went way up with corn consumption. But we really don’t see it that much in, say,  the Middle East where people started to eat wheat and barley. And even less in Far East where people started to consume rice. That leaves a complicating factor.

Zhang: You suggest that teeth have evolved to wear down over time and could even become more efficient at chewing as they’re worn down. I think my dentist would tell me wearing down my teeth is bad. So how does that work?

Ungar: I’m not necessarily sure human teeth per se are evolved to wear down. But teeth are evolved to wear in a way that keeps or makes them functionally efficient. Because if you look at prehistoric people or people today still living a traditional foraging lifestyle, like the Hadza, the group I study in Tanzania, their teeth are worn. They tend to be much more worn than our teeth. Evolution isn’t going to say oh well, we’re just going to choose shape are unworn when we’re trying to make a traditional biting machine. Nature is going to select for teeth that wear in a way that keeps them efficient.

In effect, the teeth are sculpted with wear. That has to has to do with the distribution of the very, very hard enamel on the outer part of the surface and the softer dentin inside. So when you break through the enamel and hit the dentin, it gets kind of scooped because it’s so much softer than the enamel around it. That creates sharp edges which are sometimes efficient.

In fact, in some animals, they have to have worn teeth for them to even be efficient. A lot of rodents are born with worn teeth. They actually start grinding their teeth in the uterus because they don’t function very well, if they’re not worn.

A modern hunter-gather’s worn teeth (left) and an urban dweller’s teeth (right). Both live in Tanzania. (Peter Ungar)

Zhang: I didn’t quite understand what you meant about the pattern of wear until I saw the side-by-side of photos of an urban dweller's teeth and a modern hunter-gather's teeth.

Ungar: I took those pictures about a year ago in Tanzania. The urban dweller lives in the Arusha region. He’s basically our translator and our guide. He’s an European white guy. I just compared his teeth—he lives in the area—directly with that of one of the hunter gatherers we were studying.

Zhang: Let’s go further back in the evolution of teeth, back to the first mammals. Chewing turns out to be a mammalian breakthrough. Why is chewing a big deal?

Ungar: When you ask an neontologist, somebody who studies living animals, how you define a mammalian, they’ll say hair, live birth or at least delayed egg retention, lactating. In fact, “mammal” refers to the mammary glands. But to paleontologists, these things can’t be really be reconstructed. So for paleontologists, we define mammals on the basis of chewing.

Most other animals just basically open and close their mouths. Mammals are unusual in that they either slide their teeth forward and back, if you’re a rodent, or side to side if person or a cow. That is necessary in order to break food down so when it hits the gut, it’s got lots of surface area. And it’s important for mammals because we are warm blooded. We are what’s called endothermic and being endothermic gives us some real advantages. We can be active in colder conditions and at night. We’ve got more stamina for moving around and taking care of kids. We can live in colder places, like higher latitudes. And we can move around faster to get prey. But it’s really expensive because what you’re doing is you’re creating your own furnace and you've got to fuel it. Because our metabolic rates as mammals are something like ten times higher of similar-sized other animals, we need a lot more fuel. We need to digest food much more efficiently and that’s where the chewing comes in.

Chewing is fundamental to being a mammal and having molars and premolars evolved for chewing is fundamental to being a mammal.

Zhang: Molars have to be really perfectly aligned to chew, right? I had a dental crown once that was slightly too high and it caused me no shortage of problems.

Ungar: Nearly all mammals have two sets of teeth. Other animals have a lot more. And that all comes down to chewing. Because if you’re going to chew, you have to have precise contact between upper and lower teeth. If you keep popping in and out new teeth, it’s really hard to get the relationships between uppers and lowers to be good enough for chewing.

Zhang: You write that it’s pretty obvious even to children that the sharp teeth of lions are used to rip meat the big flat molars of, say, giraffes, to chew vegetation. But when it gets to primates and early humans, it gets a lot more complicated to figure out diets based on tooth shape.

Ungar: One of the takeaways of the book is that what you’re adapted to is not necessarily what you do on a daily basis. Understanding ecology—that is the relationship of an organism to its environment—is not the same thing as studying adaptation—that is what your ancestors evolved to do. The mangabeys, for example, monkeys from Kibale in Uganda, these are animals that very, very rarely need to eat hard foods to survive. But they better have teeth that are for consuming hard foods if they need them even rarely, so that they can get through the rough times.

I like to use this analogy: If you eat Jell-O 360 days out of the year but if you’ve got to eat rocks the other five days, your teeth have better be designed to eat rocks.

Zhang: Since the overall tooth shape can’t tell you what our ancestors actually ate, you end up studying what you call foodprints. What are foodprints?

Ungar: Foodprints are like footprints in the sand, traces of actual activities of an organism that was alive. There are several different types of foodprints that are used today. One major foodprint type is the chemistry of the teeth because your teeth are built essentially from the foods you eat. Different types of foods have different chemical signatures. For example, different proportions of isotopes of elements like carbon. Those are going to be reflected in the teeth that are being formed from the foods that are eaten.

There are others. The tartar sometimes on the teeth are preserved, and you can scrape off the tartar, look on the inside, and see if there are little bits and pieces of plant material—whether it’s DNA or whether it’s phytoliths, which are little bits of silica that form in plant parts. These are sometimes identifiable as well. The DNA and stuff inside the tartar, that really has been not explored fully because people have only started to do it and  DNA doesn’t last all that long. But it’s useful for Neanderthals and early modern humans.

The foodprint I usually study is microscopic wear or “microwear” on teeth—the scratches and pits that form as a result of use. Different patterns of scratching and pitting are reflecting different diets.

Zhang: I was stunned to learn that you use the same goo dentists use to do tooth impressions for studying ancient teeth, and that goo can capture micrometer-size scratches.

Ungar: It’s pretty remarkable stuff. If you think about it this way, it’s essentially vinyl. The subtle undulations in the groove, the really subtle changes are enough to record a symphony orchestra. They sure as heck can preserve scratches on teeth.

Zhang: What does the microwear of modern humans look like? Is there very little because we eat soft foods?

Ungar: You know, we haven’t really studied modern city dwellers so I can’t say for sure. But I did take impressions of my sister’s teeth when I first got started when I was in graduate and she was still in high school. Thought it was kind of fun and entertaining. There were lots of scratches on them. But we haven’t done any formal analyses.

Zhang: Do you ever think about how future paleoanthropologist would interpret our teeth, like what they might make of fillings and braces?

Ungar: Oh man. They’ll probably be appalled. Oh god look how awful those teeth are.