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Library of Congress Cataloging-in-Publication Data

Names: Schutt, Bill, author. | Wynne, Patricia, illustrator.

Title: Bite : an incisive history of teeth, from hagfish to humans / Bill Schutt ; illustrations by Patricia J. Wynne.

Description: First edition. | Chapel Hill, North Carolina : Algonquin Books of Chapel Hill, 2024. | Includes bibliographical references and index. | Identifiers: LCCN 2024005154 | ISBN 9781643751788 (hardcover) | ISBN 9781643756158 (ebook)

Subjects: LCSH: Teeth—Evolution—Popular works. | Teeth—Popular works. | Dentition—Popular works. | Adaptation (Biology)—Popular works.

Classification: LCC QL858 .S38 2024 | DDC 599.9/43—dc23/eng/20240405

LC record available at https://lccn.loc.gov/2024005154

First Edition

E3-20241128-JV-PC-COR

Contents

Cover

Title Page

Copyright

Dedication

Epigraph

Introduction

PART I: Toothy Adaptations in Nature: The Specialists

1   Vampire Bats Don’t Suck

2   Candirus: Be Careful Where You Go

3   Horses: Long in the Tooth

4   The Tusked and the Tuskless

5   Fangs a Lot

6   Poop on the Beach: The Good Kind

7   Shrews: Tiny in Size, Major in Attitude

8   Bite This!

PART II: Who, What, Where, and How Many?

9   By the Teeth of Their Skin

10 A Painless Guide to Tooth Basics

PART III: Teeth, Who Needs ’Em?

11 Of Fish and Frogs

12 Dinosaurs, Turtles, Birds, and Dresser Drawers

13 Toothless Mammals, from Anteaters to Whales

PART IV: Human Teeth: The Bad Old Days and Beyond

14 A Man of Few Words… and Fewer Teeth

15 Jaw Jewelry, Pliers, and Pelicans

16 Tooth Worms

17 Wisdom Teeth, Baby Teeth, and the Tooth Fairy

18 To Infinity and Beyond… the Dental Chair

Epilogue

Acknowledgments

Discover More

Also by Bill Schutt

Notes

Cover

Table of Contents

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With deep respect, admiration, and gratitude, this book is dedicated to my academic and scientific mentors: John Hermanson (Cornell University), Nancy Simmons (American Museum of Natural History), and Edwin Spicka (SUNY Geneseo).

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TEETH! They are very much in style

They must be very much worthwhile!

—Dr. Seuss

Introduction

WHEN HUMANS ARE confronted by large numbers of seemingly disorganized items, they will frequently do two things—that is, if they don’t turn and run the other way. First, they’ll separate the stuff into groups based on similar appearance. Next, if those groups haven’t been named already, they’ll name them. Basically, then, in much the same way that an anonymous launderer from the past used color or the lack of it to divide a large pile of dirty clothes into two smaller piles—lights and darks—the eighteenth-century Swedish physician Carl Linnaeus (1707–1778) divvied up a dizzying menagerie of animals into vertebrates and invertebrates. Here, though, the sorting depended on whether or not the critters were sporting a vertebral column, commonly referred to as a backbone.

For his trouble, Linnaeus was christened the Father of Taxonomy, the science of separating and categorizing living things. The identity of the Champion of Darker Darks and Lighter Lights remains lost to history.

Now that we’ve got that down, let’s say you were asked to list the unique features found in the vertebrates—a group (or taxon) composed of fish, amphibians, reptiles, birds, and mammals. The vertebral column that gave them their name would be a strong first choice. Also aptly known as the spinal column, it surrounds and protects the delicate spinal cord, while providing a sturdy attachment site for muscles, ribs, limbs, and the head. Because the vertebral column is not a solid rod but is instead formed by a varying number of chain-link vertebrae, it is also flexible enough to play a key role in movement and locomotion.

Another strong candidate for our list of uniquely vertebrate features would be bone, a form of connective tissue made up of varying amounts of stony minerals (mostly calcium-rich hydroxyapatite), bendy rods of the ubiquitous protein collagen, and water. Bone tissue forms an array of skeletal structures, conveniently—though at times, confusingly—known simply as bones. A caveat here is that while most vertebrates have bony skeletons, sharks and their flattened relatives the skates and rays have done quite nicely for the past 450 million years or so with skeletons (including vertebral columns) composed of cartilage—which is essentially bone without the stony mineral salts. And though sharks apparently never had bone, there are also a few vertebrates, like the hagfish and lampreys, that lost theirs somewhere along their respective evolutionary paths to corpse munching and parasitism. For these reasons, bone occupies a spot slightly below the vertebral column on my personal list of distinctly vertebrate traits.

“What about brains?” you might ask, utilizing some of the eighty-six billion neurons that make up the human model. But after checking with official scorers back at the studios in New York, that particular feature gets the thumbs-down. The reason is that unlike the vertebral column and bone, possession of a brain isn’t limited to vertebrates. These complex organic computers evolved much earlier in invertebrate groups like insects, crustaceans, and spiders. Eventually, brains were passed on from ancient invertebrates to the ancestors of the first creatures with a vertebral column. Finally, although possession of a large brain is often considered a vertebrate trait, it should be noted that the brains of both cats (vertebrates) and octopuses (invertebrates) contain roughly two hundred million neurons.¹

Like the vertebral column and bone, there is yet another vertebrate innovation that sits near the top of our list: teeth. Teeth are that important, I will argue, because much of the diversity and long-term evolutionary success of the vertebrates can be attributed to their presence. The appearance of teeth, around five hundred million years ago, and the serious remodeling that occurred after that, enabled myriad forms of vertebrates to obtain and process food in pretty much every conceivable environment—from sun-torched deserts to oceans and rain forests teeming with thousands of species of animals and plants. This matching of organism and environment forms what is otherwise known as an ecological niche. And the ability of organisms, including plants, to successfully fit into and exploit a particular niche depends on their having evolved a suite of characteristics called adaptations. Most adaptations involve some aspect of anatomy (our molars, for example, with their broad, flat surfaces) or the behavior related to those anatomical features (like using our molars to crush or grind solid or tough food items into softer, more easily digestible bits).²

But tooth functions extend far beyond procuring and processing food. These hard, mineral-rich structures, which include variations such as tusks and fangs, often play a crucial role as defensive weapons. According to the World Health Organization, over one hundred thousand people die each year from snakebites—along with three times that number who end up with amputations and other disabling conditions. And one needs only the briefest glimpse of the upper canines of snarling dogs or baboons to know that teeth are an efficient means of expressing strength, dominance, and aggression. Less obvious is their involvement in mating behavior and even parent/offspring relationships, as when young bats use hook-tipped baby teeth to hang on for dear life as their moms navigate the night skies.

Teeth also enable animals to manipulate and change their environments. Tree-trunk-gnawing beavers and water-hole-excavating elephants may come to mind, but researchers examining tooth wear patterns have shown that Neanderthals and early modern humans also used their teeth as tools, to soften tough fibers and animal hides—a practice that continues in some cultures.

Human teeth also project information about the individual. A mouthful of well-formed teeth can portray vitality, power, wealth, and success, while misshapen or absent teeth can lead to the opposite assumption. By the time George Washington was sworn in as president in 1789, he had only a single tooth—a dismal dental condition that could have done serious damage to his standing as the leader of a newly minted nation. Over the last two decades of his life, Washington would go through at least four sets of bulky, ill-fitting dentures. And though much improved from the painful-to-wear appliances of the eighteenth century, dentures remain a source of consternation to this day.

But false teeth, dentures, and the like have been around far longer than the time of the Founding Fathers. Fashioned by ancient Etruscan artisans nearly three thousand years ago in what is now Italy, these pre–Roman Empire dental appliances were composed of filed-down animal and human teeth, and, as we’ll discover, they served a surprising purpose.

BACK IN THE animal kingdom, we’ll explore why the term “specialized diet” can be a serious understatement—as in one scale-munching fish species with jaws adapted for plucking scales from either the right side or left side of a prey’s body, but not both sides. From an evolutionary standpoint, one key benefit for the specialist is the ability to eat things that potential competitors aren’t able to eat. Vampire bats stand as a prime example, with each of the three genera using razor-sharp teeth and an assortment of unique adaptations to feed on a widespread but generally untappable resource: blood.

In contrast to those vertebrates with specialized diets are the omnivores—creatures able to consume a wide variety of food sources, though the term generally implies a diet consisting of plants and animals.

But whether a tooth belongs to a specialist or an omnivore, most of its bulk (including the jaw-gripping roots) is made up of dentin, a very bone-like noncellular mixture of hydroxyapatite, tiny tubes of collagen, and water. The tooth’s crown (the part that sticks out from the gums) is covered by a thin layer of enamel, the hardest substance found in the vertebrate body. Additionally, all teeth contain a central chamber known as a pulp cavity, which contains blood vessels and nerve endings.

Beyond the importance of teeth to their owners, much of what we know about ancient life on this planet has come from the study of teeth. While other body parts decompose, teeth are far more likely to endure the test of time, in some cases for hundreds of millions of years, as fossils. Once the tooth of a deceased animal is buried (usually under an accumulation of sediment), it is protected from the effects of general wear and tear, weathering, and erosion. Over time, water, seeping down through the soil, enters the tooth through microscopic pores in the enamel. The water carries with it minerals like silica (think sand, concrete, and glass) and calcite (think limestone and marble). In turn, these substances are transported deeper into the tooth through channels in the dentin. Eventually, the minerals solidify, leaving the tooth even harder than it was in life, and making teeth the most common vertebrate fossils by a wide margin.

Beginning in the nineteenth century, fossilized teeth enabled paleoanthropologists to begin unraveling the mysteries of human evolution. More recently, they’ve provided information on ancient diets, health, climates, and ecology. The tales told by teeth currently stretch from early humans to ancient civilizations and beyond, through periods of famine, war, disease, and starvation. Today, researchers are exploring how tooth-related techniques used to examine life events in the distant past might also be used to identify early-life stress exposure that can put individuals at risk for mental health problems.

Though extremely durable, teeth are not indestructible, as those who discovered the pleasures of refined sugar would learn beginning in the seventeenth and eighteenth centuries. Effective preventive care was then unknown, as was the concept of sterile conditions, and dental quackery was widespread and dangerous. An entry found in a London bill of mortality for a single week beginning on August 15, 1665, listed 111 people who had succumbed from tooth-related issues.

Thankfully, things have gotten better. That said, many people were shocked in early 2023 by nightmarish photos depicting the aftereffects of a widely used but unregulated dental device called an anterior growth guidance appliance (or AGGA). Attracted by claims that it could correct bite issues or overcrowded teeth and eliminate sleep apnea, all without surgery, thousands of hopeful patients shelled out an average of $7,000 to have one of these wire contraptions installed. Unfortunately, instead of health benefits, many patients received damaged gums and jaws, exposed tooth roots, and flared or lost teeth. Accordingly, the use of AGGAs has fallen off dramatically, since most dentists are no longer promoting them.

Controversial dental appliances aside, given the importance of dental health (now a multibillion-dollar industry), improvements in both preventive and restorative care continue today, with promising new therapies being developed around the world. In one such avenue of research, scientists played the role of rodent dentists. But instead of placing fillings into cavity-ridden rat teeth, they inserted stem cells into the holes they’d drilled. The results were spectacular, namely the production of new dentin by the stem cells. In another study, researchers are investigating the potential to stimulate the growth of a second set of adult teeth. The hope is that this and related advances in dental medicine will soon make typical tooth fillings obsolete and dentures a thing of the past.

Teeth of varying sizes, shapes, and functions have been integral in allowing vertebrates to take full advantage of the wealth of resources found on our planet. Not to be forgotten, though, are the microscopic organisms that live on, around, and below our teeth. Divvying up the resources (a.k.a. resource partitioning) also exists in these microenvironments, as does competition and even cooperation between different microscopic organisms. Today, investigators are looking into a link between the presence of a common bacterium (Porphyromonas gingivalis) found in infected gums and the development of Alzheimer’s disease.

Before we get to that, though, and before addressing some seriously interesting questions about the origin of vertebrate teeth, we’ll put to rest any notion readers might have that “a tooth is just a tooth”—though hammering that notion into the ground like a tent peg might be a better descriptor.

Footnotes

1 Dog brains contain around twice as many neurons.

2 Adaptations give those with them a survival edge over those without them. In doing so, they also provide individuals with a greater probability of surviving long enough to mate and pass on their genes (and their adaptations) to the next generation.