Dr. Martin Thomas Nweeia is one of the world’s leading authorities on narwhals, often referred to as ‘Sea Unicorns’.
Dr. Martin Thomas Nweeia

By Emma Yasinski

Dr. Martin Thomas Nweeia is both a dentist and one of the world’s leading experts on narwhals, an unusual type of arctic whale with a tusk – actually a tooth – that can reach ten feet in length. The narwhal is often referred to as a “sea unicorn.”

Dr. Nweeia has traveled the world – including at least 16 journeys to the Arctic – to track and study the elusive mammals. Doing so, he hopes, will not only help scientists understand the narwhal’s evolution, but also the evolution and function of our own teeth.

According to Narwhal Tusk Research, the narwhal tooth is revered by many cultures and has been for centuries. It is said, for example, that in the 16th Century, Queen Elizabeth paid 10,000 pounds – the cost of an entire castle – to obtain a single tusk. To this day, the royal scepter in England is carved from a narwhal tooth.

Dr. Nweeia, a part-time lecturer at the Harvard School of Dental Medicine, serves as curator of “Narwhal: Revealing an Arctic Legend,” an exhibit that runs through 2019 at the Smithsonian National Museum of Natural History.

Incisor recently had the opportunity to ask Dr. Nweeia a few questions about his work.

(Questions and Answers edited for length and clarity)

 

Q: Your work is fascinating. How did you become interested in this incredibly unique intersection of narwhals and human dentistry?

A: Well, I think it started by reading a book when I was in college by an author named Coenraad Moorrees, called The Aleut Dentition, where he talked about landmass theories and how teeth could give an accurate record of the migration of peoples and, in turn, how landmasses were once joined together and then separated. It was a landmark study. I was always interested in anthropology but never knew about the direct connection with teeth until I read that book.

I think just about everything I've studied [laughter] with the tusk is completely surprising, and I think that's the part that drew me there. I think if you're going to pick something to study, why not study the most unusual, right? The most bizarre, the one that confuses everybody, that's the one I think that can teach us the most.

 

Q: In 2014 you published a study about the sensory capabilities of narwhal tusks. Why is the idea that teeth and tusks are not passive instruments, but rather sensory organs, an important concept for people to wrap their minds around?

A: First of all, they wouldn't expect it. The unexpected is always fun in science. I think people too often regard teeth as these, kind of, passive instruments that we use to bite and chew our food and don't realize the wonderful array of forms, expressions, and function that teeth have played over the course of evolution.

The thing that made it unusual for the narwhal was just that it was continuously monitoring its environment all the time, whereas our teeth get stimulated by certain actions, like if a tooth broke or if we had some pathological condition that made us sensitive to cold or temperatures. But I think it's expected when you look at evolution, teeth began as sensory organs. So, to find something now, today, that ties us back to that original function was, indeed, a bit surprising.

 

I think if you're going to pick something to study, why not study the most unusual, right? The most bizarre, the one that confuses everybody, that's the one I think that can teach us the most.

 

Q: What can we learn about our own teeth from tying it back that way?

A: Some people even have trouble with the phrase “sensory organ” being attributed to teeth. We think of eyes and ears, but seldom do we think of teeth. But when you look at their embryologic origin, they're derived from all three layers: ectoderm, mesoderm, and endoderm. With that complexity comes this wide array of function.

Evolution can influence function. I've had people come up to me and say, "You know, that's interesting. My mom's an archaeologist, and she can tell the difference between a pottery shard and a stone by putting it between her teeth… That's her tried-true test in the field for knowing that difference." When we think about that, what are the other functions that we're not even aware of that we could develop?

 

Q: How similar are human teeth and narwhal tusks in composition?

A: [In both] their primary component is dentin. Our teeth are covered by enamel. Narwhal teeth, interestingly enough, really have no enamel portion that's been reported. The other part is cementum, which ties our teeth to our bone. In our teeth, cementum is only found in the roots that lock that portion to the bone, whereas the narwhal tusk is the only tusk that has a cementum layer almost all the way out to its tip. That's completely unusual. That doesn't happen anywhere else in mammals. And the other part that people seldom realize is that it has a nerve and a blood supply all the way to its tip.

Our teeth typically start with the outer component. The mineral-to-collagen ratio on the outside of our teeth is very high in mineralized component in enamel, and then as you go towards the pulp, it gets softer. There’s more collagen. Narwhals are almost exactly the opposite. They start actually very soft at the surface because of their cementum layer, then you get to a harder dentin component, and right before you get to the pulp is what's almost the equivalent of a shaft of steel. Its hardest, most mineralized, component is immediately around the pulp.

 

There's a huge body of literature that shows the association between diet and tooth morphology. What you eat is going to really determine what your teeth, in large part, will have adapted to.

 

Q: You’ve mentioned previously how difficult narwhal can be to find and study. How do you do it?

I've really been very active in incorporating Inuit traditional knowledge. And I think this is an important component because what it really is about is analogous to listening to the patient, if you're making the analogy in dental practice. You can have all the instruments in the world to diagnose a disease, but everybody knows health history is the key component.

Listening to a person is really what's going to tell you what's going on. And the same is true, I think, in the animal world when you look at something that indigenous people have spent their lives with. So, in this case, I've interviewed hunters all over northeastern Baffin Island and northwestern Greenland in the high arctic, because these people have spent thousands of years of observation with this whale and have given us incredible insights into their form, their function, their behavior, their migration, their distribution.

 

Q: What have you found most surprising in your years of studying these animals?

A: There's a huge body of literature that shows the association between diet and tooth morphology. What you eat is going to really determine what your teeth, in large part, will have adapted to. The narwhal eats very large fish as a dietary component, and yet it has no teeth in its mouth. You can't get more counterintuitive than that.

What makes it even more odd is that the whale has the capacity to form 12 teeth in its mouth and yet those are genetically silenced at birth. So not only does the animal not have teeth when it has a diet of fish that it could certainly use those teeth for, but even with the capacity to form them [it] shuts them off. Pretty wild, right?

 

Author: Contributing writer Emma Yasinski received her Master of Science (MS) in science and medical journalism from Boston University. Her articles have also appeared at TheAtlantic.com, Kaiser Health News, NPR Shots, and Genetic Engineering and Biotechnology News.

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