Science Friday - The History Of Teeth, From Ancient Fish To Humans

Episode Date: August 29, 2024

Your teeth don’t just chew your food—they connect you to the deepest of deep history on Earth. Teeth have existed, in some form, for half a billion years, making them more than 250 million years older than dinosaurs. They came before the evolution of warm bloodedness, eggs, and even limbs. From that very first set of chompers emerged a bewildering and diverse group of teeth, including narwhal tusks, sharks’ pearly teeth, snake fangs, and, of course, ours.Now teeth are the subject of a new book called Bite: An Incisive History of Teeth from Hagfish to Humans. Guest host Maggie Koerth talks with zoologist and author Dr. Bill Schutt about how teeth evolved, why they’re so neat, and what we can learn from studying them.Read an excerpt of Bite: An Incisive History of Teeth from Hagfish to Humans.Transcripts for each segment will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Vertebrate history has bite marks all over it, because in astounding ways, the evolution of teeth transformed the animal kingdom. I'd like them right up there with the backbone as the most important adaptations that vertebrates evolved. It's Thursday, August 29th, and this is Science Friday. I'm sci-fri producer Rasha Iridi. Teeth have existed in some form for half a billion years. They evolved far before warm bloodedness, before ever. eggs, even before limbs. And from that very first set of choppers emerged a bewildering and diverse group of teeth. That includes narwhal's tusks, sharks pearly teeth, snakes, bings, and of course,

our own. Here's guest host Maggie Kerth with more. Now, teeth are the subject of a new book called Bite, an incisive history of teeth from hagfish to humans. It explores a variety of toothy adaptations, how they came to be, and how their evolution helped transform the animal kingdom. Joining me is zoologist and author Bill Shutt, based in New York. Bill, welcome to Science Friday. Thanks, Maggie. It's really nice to be back. It's really nice to have you. So, Bill, is it dramatic to say that teeth changed the world, or at least that they changed the animal kingdom? No, I think that's perfect. You mentioned that they showed up around 500 million years ago. And I'd like them right up there with the backbone as the most important adaptations that vertebrates evolved.

And I think that teeth were incredibly important to allow them to obtain and process food in all sorts of different environments. And really, that was the key or one of the keys to the success of the group and the diversity of the group. Well, and they changed not just the animals, but the environment that the animals lived in, too, right? So like you get beavers that are building dams because of their teeth and parrotfish pooping out sand because they can munch on corals. Sure. And elephants digging, lifting objects, stripping bark from trees. They've got functions that don't necessarily have to do with obtaining and processing food, defense, aggression. As we've mentioned, tools, dogs and cats, for example, move their babies around with their teeth.

they express emotion. So they've been important in many, many different ways. Well, take me back to the start a little bit. So when did teeth first come about and who had the first teeth? Well, what everyone agrees on is that the first creatures that had teeth were fish. And these were ancient fish, approximately a half a billion years ago. The real discussion is where they came from. and there were really two different hypotheses.

The one that is probably the most popular right now is that there were these little bumps on the outside of these fish, and these were armored fish. So the outside of their bodies had this bony covering. And these denticles, these little tooth-like bumps, were used probably for defense. And at a certain point, this hypothesis posits that these bumps migrated into the mouth where they took on a different role as teeth. So the first teeth weren't exactly even teeth, but just these kind of bony protrusions on other parts of these fish's body.

Yeah, and that's really common. I'm really into promoting the idea that evolution is a tinkerer. It does not create things from scratch. It tweaks what's there. And there's a long list of structures that you can see had other jobs before they became lungs, for example. Lungs were structures that were called swimbladder and they were used in buoyancy and eventually evolved in some fish into lungs.

So, yeah, they had other roles first before they became teeth. Okay, so these teeth started with these ancient fish. Now they're all over the animal kingdom. And I know that one critter that you kind of have a special place in your heart for is vampire bats. So tell me a little bit about their teeth and how they use them to draw blood. Sure. I studied vampire bats for pretty much the last 30 years. And when I started my graduate career, I found out the three vampire bats. And there are roughly 1,500 species of bats and only three are vampires, that they have these adaptations that have allowed them to feed solely

on blood. They're the only mammals that they're only feed on blood. And so one of the key adaptations that they have is that they're incisors, the teeth that are up front. And the canines, the ones just to the rear of the incisors, are highly modified into incredibly sharp teeth. And they use these teeth to make a painless bite on their victims. Then they start to lap this little wound, which looks more like a divot. There's no such thing as sort of like two little puncture holes like you see in Dracula. And the saliva that they apply with their tongues has an anticoagulant, the blood starts to flow. There's a gap between the teeth and the blood flows between the teeth along a groove in the tongue, and they just, they swallow it. And the victim

is pretty much unaware of what's going on. It's either asleep or oblivious because the bite was so sharp that it didn't cause any pain. Well, how do they keep their teeth staying so sharp? Well, there is a, there's a hypothesis that they use this process called thigosis, where when the teeth closed, they sharpen themselves by sort of moving against each other. So they're, in a sense, self-sharpening teeth. Oh, my gosh. Yeah, there's been some question as to whether that really occurs or not, especially recently. So graduate students, keep your ears open. Well, speaking of the teeth that we think of as scary, let's talk about shrews. Now, shrews are cute, but their bite is not cute. So can you tell us a little bit about that? Sure. Shrews are mouse-like

little creatures, but they're not mice and they're not rodents. You know, I first encountered them when I was at school, and we went on these trips in my momology class at Cornell, and we set out traps to catch animals. And the professor, Deidre McClan, told us, well, you have to go check those traps every three hours. And we were like, why? We just wanted to hang out, you know. And she said, well, if we catch shrews and you don't check the traps every three hours, they starve to death. And I was like, really? And that's because their metabolism is so high. Their heart rate is so high that they have to eat constantly. And one of the adaptations that they have, the enamel in their teeth, and enamel is the hardest substance in the vertebrate body, also has iron in it, which makes

them even harder. Oh, wow. Yeah. The key here is that when they bite a victim, and their victims can be larger than them and often are. They deliver a venom, and that venom blocks muscle contraction. And it doesn't necessarily kill the victim, but what they do is the shrew will drag that victim, and oftentimes it's a rodent or something like that, back to their lair. This is called live hoarding, and they will keep that victim alive for weeks, and they will keep him paralyzed by just biting them every now and then. The idea here being that if you run out of food, you can always go back to your den and eat part of your victim, which is still alive, which is pretty wild.

It sounds like Shrews should actually get the vampire label rather than the bats. Yeah, they're fascinating creatures. And there were also the stars of my favorite cheesy 1950s horror movie, The Killer Shrews. And I talk about that as well. Well, let's pivot from there to our own pearly whites. what has studying teeth of early humans taught us about our own evolution? Yeah, there's a lot that we've learned about teeth.

And that's because they are so hard and they are by far in a way the most common vertebrate fossils. You know, if you've got a shark, an ancient shark that had 30,000 teeth over the course of its life, the odds of it leaving teeth in the fossil record is very high. And because they're so hard, fossil teeth are extremely common. And so we've learned a lot about them. And one of the things we've learned about human teeth and human evolution is that we used to have a longer jaw. Back in ancient times, probably somewhere around 15,000 years ago. And before that, ancient humans and their ancestors were using this extra set of molars to process tough food.

Very difficult to process, very difficult to digest. And roughly 15,000 to 10,000 years ago, as humans started to process their food in a way that made it softer, the jaw evolved and it became shorter. But in that blueprint, the number of teeth stayed the same. And so you have a shorter jaw now, but this third set of molars pops up sometime between, roughly, when you're 18 and 25 years of age. There's not enough room there. These molars crowd out the teeth that are there already and cause all sorts of problems that many people know about. You know, a lot of us have these crowded teeth and we end up with braces. And what did ancient humans' teeth look like?

Surprisingly, or maybe not surprisingly, the teeth that we find in the fossil record for humans are compared to our teeth cavity-free. And that's because they weren't eating processed sugar. And so, you know, it was just like the rest of the animal kingdom. You don't see a lot of teeth having the problems that we have today, primarily because of our diet. Well, you know, speaking of old teeth, I was kind of horrified to read some of the old school dentistry you described. Can you tell me a little bit about toothworms? Yeah. Very interesting. To me, that was one of the things where I just lit up when I came across this. And there was this belief. And it is a, it was pretty much a worldwide belief that tooth problems like cavities were caused by worms. And this was, as I said, you could find this in the, in the record of all of these ancient cultures that we don't think really had any contact with each other. You know, it doesn't matter if you were

Aztecs or Chinese or Europeans or Africans, people had problems with worms. They saw that they caused rot of wood. They were problematic with regard to crops. And so we think that this idea that dental problems were caused by teeth was sort of a natural response to, well, something bad's happening. It's probably worms. Anthropologists thought that this story, like some other things, came out of Mesopotamia or Egypt and that ancient seafarers passed these stories on. But we don't think

that's the case now. It sort of reminds me of convergent evolution where you've got different adaptations that looks very similar, like the wings of a bird and the wings of a bat did not come from a common ancestor. They emerged separately. And so we think now that these stories about worms destroying teeth popped up separately in these different cultures because people have problems with worms. How did people deal with rotting or broken teeth back then? There was not a lot of dental care. So if you would have looked back for, go back for most of the last 2,000 years of the record, there's, there was tooth pulling. It was extremely unscientific. It was seen in various cultures. But there were no specialists. There were no dentists. They were using, they might use

pliers. They might use later on things that they would build barrels with. They were using needs to yank teeth. In the middle ages, though, it got a little bit better. And so you'd go to a fair or you'd go to a market, and there'd be these tooth pullers. And these guys, once again, had no specialized tools. And they often had musicians and clowns kind of bopping around making noise to drown out the sounds of people getting their teeth yanked out without anesthesia. And there was a lot of quackery. I'm sure a lot of people died from infections. And it wasn't until later on in the Middle Ages that these barber surgeons started to emerge. And these were people who fixed broken bones and Lance Boyles and they administered enemies and they also pulled teeth.

And they scraped plaque off their teeth, which would build up. And from there, you know, modern dentistry roughly coincided with the rise in the use of refined sugar by the masses. And that took place right around. It started around the 1660s. Before that, sugar was something that only rich people had, and it came from places like India. But once you had sugar plantations in places like the West Indies and processed sugar became more available, that's when cavities became extremely problematic for people. And that's when you got these dental surgeons. They specialized only in dentistry.

And they pulled teeth and they transplanted teeth, which was a concept that I also found fascinating and incredibly strange. You get into some of like the innovations in dentistry that are coming now. What are scientists working on that you think is particularly interesting? To me, the one that we'll probably see in the near future is the fact that when you get a cavity and it gets filled, the filling is called a composite filling. And that's really inert material that they're used to fill this, this hole that they've drilled in your tooth and they've removed the bad part of the tooth and they fill it with a, composite filling. Right now they're starting to do research on regenerative fillings. The idea being you would drill the tooth, remove the part that's bad, and then replace that, stick into the hole, into the cavity, this substance that would stimulate stem cells. And these stem cells

would then produce dentin. So you're... Oh, wow. Okay. Yeah, and dentin is the bony material that makes up most of the tooth. And so you're really replacing the dent in that you've removed by stimulating these stem cells whose job it is is to produce this material. So you just grow your own new teeth? Yeah. So that's one I think you're going to see, I don't know, hopefully within the next 10 years of cell. But then there's other research too that's really exciting. And there are researchers in USC, for example, who are studying alligators. And alligators can have over 50 different sets of teeth. the thing is that the sockets that their teeth fit into are similar to those found in humans. And there is a layer in that socket and as a tooth begins to grow, that stimulates tooth growth.

And for alligators, that layer stays active for the life of the animal. It just keeps cranking out new sets of teeth as the, as the, as the, as the, as the, as, as the, as, as, as, as the, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as, as the, the previous ones are knocked out. In humans, that layer becomes dormant. So these researchers are trying to figure out a way to stimulate that dormant section, that layer called the dental lamina to reinvigorate and to produce another set of teeth. Really growing your own set of teeth. Wow, that's super cool. Just to kind of wrap things up, Tell me a little bit about how all of this has made you think about your own teeth differently. I don't know if I think about my own teeth differently, but I realize now that teeth, including human teeth, that does far more interesting stories to tell about them.

The fact that they exist in just this dizzying array of forms, how valuable they've been to. us. That's so cool. And I think the fact that that dentistry is changing and and there are sorts of there are all sorts of innovations now that are that are making that feel something really exciting. Well, Bill, thank you so much for joining me today. Oh, it's a pleasure. Thanks for having me back on. Bill Shutt is the author of Byte, an incisive history of teeth from hagfish to humans. He's based in New York. You can read an excerpt from his book on Science Friday.com slash bite. And that wraps up today's show.

Lots of folks help make it happen, including Dee Petersmith, Felissa Mayors. Emma Gomez. Jackie Hirschfeld. Join us tomorrow for a roundup of this week's science news. Catch you then.

I'm CyFRI producer Rasha Iridi.