This is a transcript of the Gastropod episode The Truth is in the Tooth: Braces, Cavities, and the Paleo Diet, first released on October 20, 2018. It is provided as a courtesy and may contain errors.

PETER UNGAR: The teeth themselves are huge. They have extremely thick enamel on the teeth. They’re big and flat structures. And they were initially thought to be designed basically to be used as a nutcracker.

NICOLA TWILLEY: Meet Nutcracker Man. That’s not who’s talking—he’s Peter Ungar and his teeth are pretty normal.

CYNTHIA GRABER: But Nutcracker Man—he was from a species before humans, and he lived millions of years ago. His teeth are massive and thick and they clearly were meant to crack apart meaty nuts. Right?

TWILLEY: Well, that is the question, isn’t it? This episode is all about teeth—and what they can tell us about what we have eaten and what we should eat.

GRABER: We of course are Gastropod, the podcast that looks at food through the lens of science and history, I’m Cynthia Graber.

TWILLEY: And I am Nicola Twilley. And this episode we are going to take you on a dental detective adventure. What clues can our ancestors’ choppers tell us about what we humans evolved to eat?

GRABER: What are teeth, and why did animals evolve them in the first place? And are our teeth still evolving today?

TWILLEY: And what’s with cavities—did our ancient ancestors get those too?

PRE-ROLL

UNGAR: Nutcracker Man is a species that’s known in the scientific world as Paranthropus boisei.

TWILLEY: Like we said, this is Peter Ungar. He is a professor of anthropology at the University of Arkansas. He’s the author of a recent book called Evolution’s Bite. And he loves Nutcracker Man.

GRABER: Nutcracker Man was not a human—we humans weren’t around yet—but Peter describes him as being on the human side of our split from our cousins the chimpanzees. He’s an early hominin, to be precise.

UNGAR: And Nutcracker Man lived between about 2.3 and 1.3 million years ago in Eastern Africa.

TWILLEY: But his fossilized skull? That was found just sixty years ago, by an archaeologist called Mary Leakey. She was fossil hunting in a gully in Tanzania. And as she swept the top soil away, she saw two massive teeth and huge curved jaw. And, apparently, she shouted, I’ve got him!

GRABER: Mary and her husband Louis gave this young dead man and this species a scientific name, Paranthropus boisei. But soon everyone was calling him something else.

UNGAR: Well, the jaw and teeth look like a nutcracker. Basically the jaw is extremely big and heavy and it has scars that suggest massive muscles would have attached to it. The teeth themselves are huge. They have extremely thick enamel. They’re big and flat.

TWILLEY: Peter has spent his career studying teeth. Specifically, what teeth can tell us about our ancestors and what they were eating.

UNGAR: My postdoc and I and colleagues had spent years looking at the various species of human ancestors. And I basically gave the other species to my postdoc to work up. But I love Paranthropus boisei. It’s just so unique, so different, so distinctive that if we can’t figure out its diet we’re pretty much out of luck for anything else. So I wanted to do that one myself.

GRABER: But it’s not like these teeth are easy to get a hold of, or like they can be shipped to you. Peter had travel to National Museum of Tanzania.

UNGAR: I went to the museum and I took impressions of the teeth with the same vinyl material that your dentist uses when they’re preparing your crown for you. So, as soon as my postdoc left and went on to his own tenure track job, I took these teeth. I stuck them under the microscope.

TWILLEY: And what Peter saw there, shocked him. In fact, he almost didn’t believe his eyes. His colleagues certainly didn’t believe him. Because it looked like Nutcracker Man wasn’t eating nuts after all.

GRABER: And this is the mystery we are now going to explore. Why did Peter expect to see one thing—and what did he find instead? What did the teeth tell him?

TWILLEY: As it turns out, teeth have plenty of stories to tell.

TANYA SMITH: Well, teeth can tell us a lot about our development. About stress as we’re growing up. About how long it takes us to reach adulthood.

GRABER: Tanya Smith also studies teeth, she’s a professor at Griffith University in Australia. And she has a new book called The Tales Teeth Tell.

SMITH: Teeth can tell us a lot about our evolution. About relationships between different fossil groups. How much we traveled in in our ancestral lifestyles. Teeth can tell us a lot about our behavior. About what we were eating in the past.

TWILLEY: All of these stories are there for the telling in teeth. If you have them. Because not every living creature has a set of pearly whites.

GRABER: And of course our very very very ancient ancestors—none of them had teeth.

SMITH: So organisms could you know open their mouths and collect things in the water or filter particles in the water.

TWILLEY: Which is a very passive way of getting hold of dinner. But then there was a breakthrough.

SMITH: So early vertebrates seemed to have evolved Jaws in some cases before teeth.

GRABER: Jaws helped those filter feeders eat because they could crush their food. But those jaws didn’t necessarily have any teeth in them.

TWILLEY: In fact, no one quite knows where teeth came from—but it probably wasn’t jaws, originally.

SMITH: Some of the earliest vertebrates on the order of 500 million years ago had these kind of bumpy armored plates on their heads. And these bumpy plates had little—what are called dentacles or toothlike projections. And originally they were thought to provide a defensive mechanism on the outsides of their heads.

GRABER: These dentacle things, they’re also called skin teeth. And the ones closer to their mouth? Those might have been useful for biting down on other creatures at dinner time. The theory is that some of those body-covering skin teeth might have slowly over evolutionary time moved into the fish’s mouth.

SMITH: That’s one theory. There’s another theory.

TWILLEY: This second theory involves very strange eel like creatures called conodonts that had lots of little teeth-like bumps in their throats.

SMITH: They’re called pharyngeal dentacles. They’re these kind of strange pointy structures. They may have served a kind of processing function in the throat area of these early vertebrates.

GRABER: And like in theory number 1, the thought goes that maybe these throat teeth slowly, again over evolutionary time, migrated into the animals mouths.

TWILLEY: All of these early tooth prototypes, they have one thing in common. They’re all just very simple peg-like shapes. But they set off an evolutionary arms race.

SMITH: Well, anything that allows us to break down our food more efficiently before it gets into our digestive system helps us out. We have to spend less energy breaking down food metabolically and chemically, if we can start to process it physically with teeth.

GRABER: And so the creatures that didn’t develop teeth, they were at a disadvantage, because they couldn’t process food as easily. So more and more animals developed teeth in order to compete.

UNGAR: Once teeth took over, they really took over. There was a long period of time in which there were basal vertebrates, things like lampreys and hagfishes that didn’t have jaws or teeth. And they dominated the oceans for millions and millions of years. We’re here now and they’re mostly gone.

GRABER: And that is because of teeth.

TWILLEY: But wait up—what actually are these magical food processing secret weapons

SMITH: What are teeth? Well, teeth are the hard mineralized structures in our mouths.

GRABER: The enamel on our teeth is the hardest tissue in our entire bodies, it’s 95% mineral, basically it’s like a rock.

TWILLEY: So for those first vertebrates this is kind of like their own stone age— suddenly they have stone tools in their mouths that they can use in all kinds of ways.

GRABER: And evolution helped different animals build different sets of stone tools in their mouths.

TWILLEY: Some early birds grew their teeth into hook shapes to catch fish. So teeth become a way to acquire as well as process food.

GRABER: Once animals moved onto land, some huge meat-eating reptiles basically grew sharp blades in their mouths to tear up their prey.

TWILLEY: Some animals have even evolved multiple rows of teeth. Basically, any kind of tooth that you can think of to give you an advantage in eating, some creature has evolved it.

SMITH: One group of primates called lemurs have these projecting lower incisors that stick straight out and actually form a comb-like structure. And they can use this sort of projecting comb both to groom themselves and one another but also to actually gouge tree bark and bite into a tree to get it to produce sap.

GRABER: It wasn’t an entirely straightforward evolutionary line. Some animals got rid of their teeth for tools that were even more useful to them. Toads dropped teeth in favor of a meal-grabbing tongue. Birds gave up teeth for their sharp beaks.

TWILLEY: But they retained the ability to make just one special tooth, right before they hatch—the egg tooth.

SMITH: This egg tooth is just a transient structure. It just grows out and allows them to kind of tap their way out of the egg and then it’s shed because they’re not going to obviously use it for chewing food.

GRABER: There’s one innovation that you mostly find in mammals, and these are the brilliant invention called molars.

UNGAR: When the molar was invented—when it first appeared—its function was more for processing food, for fracturing and fragmenting food.

TWILLEY: Even a little peg-like kind of tooth would help with this process. But molars just crushed the food, literally—which of course gives your digestive enzymes more surface area to attack, which in turn means that your dinner can be turned into energy much more efficiently.

GRABER: Like we said, as animals evolved teeth, these teeth were fine tuned to match the animal’s food. Like those birds with their hook teeth to catch fish, or the carnivorous early reptiles that had blades to slash meat.

TWILLEY: But what that also means is that, in theory, you should be able to tell what an animal eats by just looking at its teeth.

UNGAR: Well, just looking at the teeth of a giraffe and a lion it’s pretty clear that that they must eat different things, right? A giraffe has these flat, plate-like teeth with tiny ridges running parallel to one another, kind of like a washboard. And that’s clearly used for grinding tough vegetation. Whereas if you look at a lion’s tooth it looks like a sharp blade. It looks like a knife and it’s used for slicing—meat and sinew and things of that nature. And it’s pretty clear just by looking at these things, it’s intuitive, that these animals have very different diets and their teeth reflect that.

GRABER: The earliest person to start to figure out how shapes matched diet was a guy named Edward Drinker Cope.

UNGAR: Edward Drinker Cope was a 19th-century paleontologist. And how he figured it out, I’ll never know. It was really remarkable.

TWILLEY: Edward Drinker Cope was obsessed with fossils. He was a bone hunter during the big bone wars of the 1800s, when wealthy Americans were digging left and right to try to score fossil trophies.

GRABER: And Edward scored quite a lot of them. He collected more than 13,000 fossil specimens, and he published more than 1,400 papers. And he was particularly obsessed with teeth.

TWILLEY: Edward spent years looking at his fossils, trying to figure out how and why all these different shaped molars evolved. Finally, in 1883, he presented his master theory to the American Philosophical Society. In his talk, Edward showed the astonished crowd how one basic three-cusped shape got tweaked—so, like, over time dogs lost one of the three bumps to create a saw like effect for eating meat. And horses added another cusp to create a grinding mechanism for their grass-based lifestyle.

GRABER: Edward’s theories matched teeth shapes to diet.

TWILLEY: But what if you tackled this problem the other way round—from the point of view of the food?

GRABER: That’s what Peter Lucas did. He’s an anthropologist who took an engineering approach to teeth.

UNGAR: He really introduced the idea of fracture mechanics. Some foods protect themselves from being eaten by hardening their tissues, making it very difficult to start a crack in them. Others protect themselves from being eaten by toughening tissues, making it very difficult to spread the crack through them.

GRABER: And so Peter Lucas could start to imagine what tool might be the most efficient and most effective to break down that food.

UNGAR: And so he built models for the most efficient teeth for breaking down given foods. And the idea then is to use these models and see how close to the mark nature actually comes.

TWILLEY: So Peter Lucas came up with an ideal tooth shape for tough foods like raw meat—it was a wedge shape.

GRABER: And he designed the ideal tooth for a super hard food like a nut encased in its shell.

UNGAR: So what you want to do is you really want a hemispherical or dome shaped tooth because that minimizes the contact point but also maximizes the strength of the tooth itself.

GRABER: This ideal nut-cracking tooth—this is exactly what Nutcracker Man had. He had big dome-shaped, heavily enameled teeth that looked like they were perfect for cracking into walnuts.

TWILLEY: And so here’s the moment of truth. His post doc has gone, and Peter Ungar finally gets a chance to look at Nutcracker Man’s teeth under the microscope…

UNGAR: I was expecting to see tiny little pits all over the surfaces. Because typically when a primate crushes hard foods, the teeth get pressed into the food and the opposing teeth are pressed together which creates pits. So that’s what I was expecting to see because it looked like this Nutcracker Man had evolved to eat nuts.

GRABER: But to Peter’s great shock, that’s not what he saw. Instead of tiny pits, all he saw was wispy scratch marks. Tooth after tooth after tooth, wispy scratches.

UNGAR: And I was totally not expecting that. I was expecting the teeth to look like the surface of the moon. But just these fine wispy scratches running on the surface. It was completely unexpected.

TWILLEY: So Peter published. And he said that Nutcracker Man was not eating nuts. Instead, he said, the ancient hominin formerly known as Nutcracker Man was actually eating a lot of grasses.

GRABER: It was hard enough for Peter to convince himself that what he saw was, well, what he saw. And his colleagues?

UNGAR: A lot of people wouldn’t buy it. Because they said, well, it’s not possible. Look at the shapes of the teeth and the jaws, they must have been eating hard foods. You don’t know what you’re talking about.

TWILLEY: There is a lot to untangle here. I feel a little like Peter’s colleagues. Why would Nutcracker Man have the right teeth and jaws for cracking nuts and not be using them?

GRABER: And how can the story of Nutcracker Man help us understand more about what our own ancestors were eating? What can our teeth tell us about those early paleo diets?

MID-ROLL

TWILLEY: To understand Nutcracker Man, we need some help from the gorillas.

UNGAR: The first gorillas that were ever really studied were the gorillas in the Virunga mountains of Rwanda.

GRABER: There are a lot of people who live at the base of these Virunga volcanoes—in fact, it’s the most densely populated rural region in all of Africa, because the soil there is so great for farming.

UNGAR: And all the wild animals that lived around the base of the volcano were sort of pushed up to higher elevations by encroachment of humans. And that includes the gorillas. And so now the gorillas are living up in the mist of the high altitude in the mountains.

TWILLEY: These gorillas are famous gorillas. They were made famous by Dian Fossey and her book Gorillas in the Mist. And, for quite a long time, everything we knew about gorillas was based on this group.

UNGAR: They basically lived in these extremely high elevations and they consumed what’s called terrestrial herbaceous vegetation. Things like wild celery, largely tough stems and leaves and things of that nature. And it made perfect sense because gorillas have sharp crested teeth. They’ve got massive guts that house microorganisms that help them break down the cellulose, the chemical that protects the cell walls in these things. And it made for a great story and it made perfect sense.

GRABER: But then some other researchers got to know another population of gorillas. They didn’t live at high altitudes, they lived in the lowland rainforests of the Congo Basin.

UNGAR: And in fact they eat soft fruits most of the time. And that was pretty surprising because their teeth don’t look like the teeth of soft fruit eaters.

TWILLEY: This was confusing to teeth people like Peter. Why would gorillas have leaf teeth if they preferred fruits?

GRABER: For the answer to that, you have to understand something teeth people now call fallback food.

SMITH: A fallback food may be something that during the tough time of year an animal is sort of left with no choice but to eat. One of my favorite examples is the Borneo orangutans that sometimes eat bark from trees.

TWILLEY: Borneo orangutans don’t really seem to get excited about bark. It’s not a preferred menu item. But they have the right teeth to eat bark because sometimes they have to, to survive.

GRABER: Just like the Congo gorillas. They might love fruit, but fruit aren’t always around, so they have leaf teeth for when they just can’t get a hold of fruits like, say, a sweet, juicy fig.

UNGAR: Which is a couple of months out of the year. So at least during those couple of months having these long crested teeth gives them an advantage.

TWILLEY: This adds a little wrinkle to the whole Edward Drinker Cope-Peter Lucas story of diet and tooth shape.

UNGAR: Teeth are important, because they’re the utensils that you have to eat with. But the real story is in availability. It’s in what nature has set out on that buffet table. That’s what dictates predominantly what the animal eats. That’s why the gorilla in the high Virunga mountains doesn’t eat fruits—because there are no fruits available to it.

GRABER: The Virunga mountain gorillas love fruit, they just were pushed far away from it by us humans and so they were eating their fallback foods, the ones their teeth shape evolved to be able to eat. So what this means is that the shape of an animal’s teeth—well, it’s just not enough to tell us what that animal was actually eating most days.

TWILLEY: But it’s pretty much all we have, when we’re trying to understand the past. We can go look at gorillas eating today. All we have of our ancestors is their bones and teeth.

GRABER: But there is another clue teeth can provide for us, beyond just their shape.

TWILLEY: And that brings us to what Peter was looking at through his microscope—those wispy scratches on Nutcracker Man’s teeth.

UNGAR: It was my old postdoc adviser Alan Walker who first noticed that animals have scratches on their teeth and first realized that that could probably be used to reconstruct diet.

GRABER: These little scratches are what Peter calls foodprints, like fingerprints for food. And Alan thought these marks should be able to help us see not just what an animal is able to eat, but what it’s actually eating.

TWILLEY: It was an exciting idea—but Alan needed to test it.

UNGAR: He was working at the time in Nairobi at the University of Nairobi teaching anatomy and one day he walked into a bar in Nairobi and in walks Hendrik Hoeck.

GRABER: So exciting! Because Henrik Hoek studied these little rodenty creatures that are weirdly actually related to elephants. They’re round, pointy-nosed furry creatures with some scary looking fangs.

UNGAR: Alan sat down and described this sort of experiment that he needed to do to Hendrik Hoeck and Hendrik said I’ve got the perfect animals for you. They’re called hyraxes and they live in the Serengeti. There’s two species. Their teeth are virtually identical. And they actually live in the same place—in fact they inhabit the same little holes. But their diets differ. So you have the same shape tooth, you’ve got the same environment, but you’ve got differences in diet.

TWILLEY: Amazing. All the other variables are controlled.But the bush hyraxes, they eat bushes. And the rock hyraxes—they do not eat rock, they also eat bushes, except during the rainy season when they like to dine on the young tender new grasses.

UNGAR: And so Alan said, you know, I’m going to go and I’m going to look at the microwear on their teeth and see whether it differs as well. And he found out that in fact it did differ.

GRABER: Great! And even better, the marks on the hyrax teeth changed with the season. When the rock hyrax ate grasses, their tooth looked one way. But when those rock hyraxes ate bushes, the marks looked exactly like those from the bush hyraxes that also ate bushes.

UNGAR: So not only can you tell the difference between the species, but you could even tell the difference between microwear within a species depending upon the season and the food that was being eaten at that point in time. And that’s sort of where microwear began to take off. People started to realize that patterns could change over time, and that they could reflect seasonal differences in diet, which is a very powerful tool.

TWILLEY: This strength is also microwear’s weakness—it’s only a record of what a tooth’s owner has been eating recently, just within the last few days.

SMITH: Yeah, people have sort of speculated that you may be looking at the quote unquote Last Supper signature.

GRABER: The other thing is that these little scratches and pits— they are not just small, they are tiny.

UNGAR: If anybody got a fingerprint on the tooth, the fingerprint grease would completely cover the microscopic wear. Because the wear itself is usually less than a thousandth of a millimeter deep. So anything is going to coat it.

TWILLEY: That makes this microwear very easy to miss or mistake—Tanya’s not actually a fan of tooth wear evidence for this reason. But a lot of research has been done on it, and Peter’s confident that with care, these tiny traces hold valuable information.

GRABER: So this takes us back to Nutcracker Man and his wispy scratches. His massive, enamel-thick teeth, they may have evolved for eating nuts when nothing else tasty was available. Maybe nuts were his fallback food, like bark for the orangutans.

TWILLEY: But that’s not what he was eating in the days before he died—he was eating grasses. And they left telltale scratches on his teeth.

GRABER: And those grasses, those could have been early carbs, the ancestors of today’s grains. Which some people argue we should never have started eating in the first place. And they base their arguments in part on our teeth.

TWILLEY: And all the cavities we modern humans have in them. Which other animals hardly ever get.

GRABER: And what about braces? Gorillas certainly don’t sport those.

MID-ROLL

GRABER: As we’ve heard, the scratch marks on teeth just represent what an ancient human had most recently eaten. It doesn’t tell you anything about how frequently they ate that food, whether all their relatives were eating it…

TWILLEY: You could get that kind of picture if you had a lot of ancient teeth to study. But that’s not a luxury Peter and Tanya have.

UNGAR: For some species the number of teeth that are represented by that species can fit in a shoe box, if not your hand.

GRABER: So teeth people have developed a number of tools to squeeze all the information they can out of rare teeth. They can use the shape. They can use the marks left by food. And they can use all the gunk that builds up on teeth.

SMITH: And in the past, prior to electric toothbrushes, ancient humans and earlier hominins would build up strong deposits on their teeth particularly near the gum lines. And these deposits trap different things that the individuals were eating during their lifetimes in basically layers on the outsides of their teeth. And so you can probe—actually go in with a little dental scraper and chip off a tiny piece of calculus, this mineralized plaque, and look microscopically at what’s inside to get a sense of what an individual might have been eating.

TWILLEY: It’s actually this mineralized plaque that recently reshaped what scientists think the Neanderthals were eating. People had thought they were hypercarnivores, basically eating almost only meat.

GRABER: But then scientists took microscopic chips from those Neandertal teeth, and they found something not at all meaty—some dates, some beans, and some barley.

SMITH: They had evidence of starches trapped inside their calculus and even in some cases starches that had been cooked, because the starch undergoes a chemical structural transition when it’s heated.

GRABER: This is an example of how new discoveries in teeth have totally reshaped our understanding of an entire group.

TWILLEY: Teeth for the win. But sometimes even teeth people have to look beyond teeth to try to put together the puzzle of what our ancestors were eating.

GRABER: When Peter was trying to understand Nutcracker Man’s diet, he also had to look at what was happening to the environment where Nutcracker Man lived in East Africa.

UNGAR: And lo and behold the Savannah was just starting to spread throughout Africa at this time. And so it all fit together really neatly—when we got these other lines of evidence—into a new story.

TWILLEY: In a way, this new story—it makes Nutcracker Man’s teeth very human-like, this ability to adapt to new conditions and a new diet. We’re famous for being omnivores.

SMITH: I talk in the book about our teeth being an oral Swiss Army knife. So we have different types of teeth in our mouth that have different functions. We have incisors that are good for biting into things and we have molars that are good for crushing things up. We have canines that are kind of intermediate that can be used for cutting to some degree.

GRABER: Tanya’s point is that we humans have teeth that can eat all kinds of foods. And the wear patterns that Peter studies? They prove that we did actually eat all kinds of foods, too.

TWILLEY: In fact, Peter says the closer you get to modern humans, the more kinds of food we ate—the story is there in the scratches and marks on our ancestors teeth.

GRABER: The species that lived before humans, Australopithecus? Peter says the scratches on their teeth are basically all the same, they had a pretty narrow diet.

UNGAR: But when we get into the earliest members of our own biological genus Homo habilis, their micro wear pattern is much broader. And when we get into even later hominins—things like Homo erectus and Neanderthals— then their pattern is even broader suggesting the consumption of even broader spectrum of food. And in fact I’d go one step further and say that the fact that these diets vary is kind of what makes us human and what makes us unique.

TWILLEY: When you ask teeth people what our ancestors ate, this is the answer. We ate it all.

SMITH: It’s clear from dental research that ancient humans and hominins ate many things. They ate different diets depending on where they lived, depending on what point in time you’re looking at.

GRABER: People who are big fans of the paleo diet—and there may be some of you out there listening now—there’s this idea that we have to go back to what our ancient human hunter-gatherer ancestors would have eaten. Tanya and Peter both have problems with this idea.

SMITH: The one thing that we’ve learned, by looking at living primates and fossils, is that diet varies over time and over space, even for a given species. I think the secret here, the issue here, is that there was no single ancestral diet to which we all evolved.

TWILLEY: So based on our teeth, the whole idea of a paleo diet—there’s no such thing. But paleo fans have another tooth story they like to tell: they say that with the invention of agriculture and adding lots of starches to the diet, that’s when you start to see cavities. The theory is if you eat like a hunter gatherer, you’ll never need a filling again. There are some folks who say the paleo diet can even reverse tooth decay.

GRABER: I am going to go on the record here: that is not true.

SMITH: We have evidence of cavities going back several thousand years in—even in hunter gatherers.

TWILLEY: Sorry paleo peeps. That said, both Tanya and Peter agree that there is an uptick in the number of cavities in the mouths of early farmers compared to hunter gatherers.

GRABER: But the story is a little complicated. It’s actually a story about microbes, not agriculture.

TWILLEY: Drink!

GRABER: Everyone’s mouths have lots of bacteria in them—it’s your mouth microbiome. Maybe you’ve heard of the gut microbiome. And the mouth microbiome seems to have shifted with agriculture. Suddenly there were more of the type of bacteria that can lead to cavities. Maybe because starchy foods have more available sugars in them.

TWILLEY: But the rate of cavities—that didn’t skyrocket till the Industrial Revolution, when pure sugar became cheap and plentiful.

SMITH: So it may be the case that there’s this sort of perfect storm of this bacteria becoming more common in the mouths of early agriculturalists. And then, you know, we sort of supercharged it by feeding it lots of sugar in the last few hundred years.

UNGAR: There’s a small increase with the onset of agriculture particularly in the New World. But the real big increase comes much later with table sugar.

GRABER: Our diet wasn’t the only thing that was changing thousands of years ago. The way we prepared foods—that was changing too.

UNGAR: In the Middle East, say, when pots come into fashion, when pottery becomes common and people start cooking in pots, you start to get stews and things of that nature which are softened, the tooth wear, it goes down.

GRABER: That’s a good thing, our teeth don’t wear down as quickly.

TWILLEY: Although that softening up—that may have been messing up our teeth in other ways. Turns out, our teeth have been shrinking.

SMITH: Well, the origin of our genus and species, Homo sapiens, was about 300000 years ago. And those early Homo sapiens had bigger teeth than we do today.

GRABER: Maybe 10-15 percent bigger. That’s a lot.

TWILLEY: And the theory is that we have all of our fancy stone grinders and food processors to blame for that shrinkage.

UNGAR: And it seems as if tool use, tools that are used for processing food really, you know, relax the pressure, the selective pressure that nature imposes on teeth. Right? If you can cut your food up with a knife you may not need sharp bladed teeth. That doesn’t mean that you’re going to evolve away from it. It just means that there’s less selective pressure towards maintaining those teeth. And so they’re going to start to drift.

GRABER: Softer foods, less need for huge strong teeth to break down that food. And that’s affected the actual size of our jaws, too.

SMITH: Well, there’s an overall decrease in our facial size. Our jaws have gotten smaller. The architecture that makes up our faces has decreased over time.

TWILLEY: Again, the blame for the shrinkage goes to our tools but also to the ability to cook food and make it softer that way. We aren’t relying on powerful jaws and stacked molars to grind tough food anymore—we’ve outsourced that.

GRABER: Wonder why so many people have to get their wisdom teeth out? Why so many people have to get teeth removed or get braces because their teeth are too crowded in their jaws? This is why.

SMITH: In the past before we relied so heavily on soft food or even domesticated foods, young individuals were eating harder foods. They were probably chewing longer. And that actually helped for bones to grow to be larger, more robust, which allowed our teeth to erupt into them and fit together properly.

TWILLEY: Whereas someone like me, eating a modern diet of lovely soft things, many of them super processed, most of them cooked—yeah, my wisdom teeth were impacted and had to be ground down and vacuumed out of my jaws. And I only recently got out of braces!

GRABER: That is because you are British and you waited far too long for your braces. I had to deal with all that when I was a teenager. That said, maybe you were better not getting braces during those horrible teen years.

TWILLEY: Because it’s such a rocking look for a grown up? Anyway, now I have beautiful American teeth.

GRABER: Yes. But here’s the thing I think is crazy cool about this story from an evolutionary perspective: Our jaws haven’t totally become smaller genetically. We still have the same number of teeth we’ve always had, but they don’t fit in our jaws. Because we’re not using our jaws with enough oomph to force them to grow big enough.

TWILLEY: And this is something we can do something about. Teeth— we can’t change. Jaws? Those are bone, and bone can grow bigger in response to pressure.

SMITH: I mean, you think of classic tennis players who spend years and years serving with their right arm and actually their bone can enlarge relative to their left arm.

GRABER: This is news you can use, at least if you’re five years old

TWILLEY: It was too late for me. But there may be a way to dodge braces in the future.

SMITH: So if you wanted to create the best conditions to have a sort of well-fitting set of teeth I would start potentially at a younger age. To be fair this is something that orthodontics are testing now, so there’s research going on. I have a colleague in France who’s been designing these experiments where he gives young children kind of this hard gum effectively—something like a hard object that they can chew and do these jaw exercises for upwards of an hour a day. And he’s really testing how how then do these children do over time? Are they less likely to need braces?

GRABER: This is all still being studied. So we don’t know for sure that it works. But if it does, would it even be a good idea? I mean, sure, maybe your teeth will fit your jaw, but what if you’re the only one who has a big jaw in our small-jawed world? I’m not sure that’s necessarily the outcome you want.

TWILLEY: It might become a new marker of the elite—you know, private school, music lessons, and a massive jaw.

GRABER: But Tanya thinks our jaws are still going in the opposite direction.

SMITH: Yeah, I was just talking to my students about what future humans will look like. Everybody wants to know. I can only imagine that you know as as we transition onto softer and even more easy to process foods or things that you can just drink through a straw we’ll have potentially even more problems with with teeth not fitting together, with impaction. And our jaws will probably continue to get smaller.

TWILLEY: Before talking to Tanya and Peter, I would have said that teeth were low on my list of interests. But it’s truly kind of amazing how much teeth can tell us about ourselves—what we’re eating, what we used to eat, how we’re cooking and processing it—so many stories.

GRABER: And if for some reason you actually remember the very beginning of this episode, you’ll remember that Tanya told us there’s even more stories teeth can tell—when we were born, where we lived, where we traveled. And we’ve saved that for our special supporters email. But yes, Peter and Tanya have convinced us that teeth are totally worth our attention.

UNGAR: You know the reality is I’ve spent my whole life studying teeth but I don’t really care about them, right? I see them as a bridge to understanding the past more generally. I see them as as a way of getting at diet. And diet is really the most intimate part of the relationship between an animal and the environment in which it lives. That part of the environment that it takes into its body to sustain itself. Right? And so if we can use teeth to get at diet we can say something about the relationship between an organism and its environment.

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TWILLEY: Thanks this episode to Tanya Smith. Her new book is called The Tales Teeth Tell, and we have a link to it on our website, gastropod.com. Where you can also find a link to Peter Ungar’s book, Evolution’s Bite—a huge thanks to him too. We’re back in a couple of weeks with a special two-part story, looking at brand new research on artificial sweeteners and soda taxes—and the results are surprising.

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