Read Online Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body by Neil Shubin - Free Book Online Page A
Authors: Neil Shubin
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ultimately helped Randy find an “inner skate.” The connections among living creatures run deep.
CHAPTER FOUR
TEETH EVERYWHERE
T he tooth gets short shrift in anatomy class: we spend all of five minutes on it. In the pantheon of favorite organs—I’ll leave it to each of you to make your list—teeth rarely reach the top five. Yet the little tooth contains so much of our connection to the rest of life that it is virtually impossible to understand our bodies without knowing teeth. Teeth also have special significance for me, because it was in searching for them that I first learned how to find fossils and how to run a fossil expedition.
The job of teeth is to make bigger creatures into smaller pieces. When attached to a moving jaw, teeth slice, dice, and macerate. Mouths are only so big, and teeth enable creatures to eat things that are bigger than their mouths. This is particularly true of creatures that do not have hands or claws that can shred or cut things before they get to the mouth. True, big fish tend to eat littler fish. But teeth can be the great equalizer: smaller fish can munch on bigger fish if they have good teeth. Smaller fish can use their teeth to scrape scales, feed on particles, or take out whole chunks of flesh from bigger fish.
We can learn a lot about an animal by looking at its teeth. The bumps, pits, and ridges on teeth often reflect the diet. Carnivores, such as cats, have blade-like molars to cut meat, while plant eaters have a mouth full of flatter teeth that can macerate leaves and nuts. The informational value of teeth was not lost on the anatomists of history. The French anatomist Georges Cuvier once famously boasted that he could reconstruct an animal’s entire skeleton from a single tooth. This is a little over the top, but the general point is valid; teeth are a powerful window into an animal’s lifestyle.
Human mouths reveal that we are all-purpose eaters, for we have several kinds of teeth. Our front teeth, the incisors, are flat blades specialized for cutting. The rearmost teeth, the molars, are flatter, with a distinctive pattern that can macerate plant or animal tissue. The premolars, in between, are intermediate in function between incisors and molars.
The most remarkable thing about our mouths is the precision with which we chew. Open and close your mouth: your teeth always come together in the same position, with upper and lower teeth fitting together precisely. Because the upper and lower cusps, basins, and ridges match closely, we are able to break up food with maximal efficiency. In fact, a mismatch between upper and lower teeth can shatter our teeth, and enrich our dentists.
Paleontologists find teeth wonderfully informative. Teeth are the hardest parts of our bodies, because the enamel includes a high proportion of the mineral hydroxyapatite—higher even than is found in bones. Thanks to their hardness, teeth are often the best-preserved animal part we find in the fossil record for many time periods. This is lucky; since teeth are such a great clue to an animal’s diet, the fossil record can give us a good window on how different ways of feeding came about. This is particularly true of mammal history: whereas many reptiles have similar teeth, those of mammals are distinctive. The mammal section of a typical paleontology course feels almost like Dentistry 101.
Living reptiles—crocodiles, lizards, snakes—lack much of what makes mammalian mouths unique. A crocodile’s teeth, for example, all have a similar blade-like shape; the only difference between them is that some are big and others small. Reptiles also lack the precise occlusion—the fit between upper and lower teeth—that humans and other mammals have. Also, whereas we mammals replace our teeth only once, reptiles typically receive visits from the tooth fairy for their entire lives, replacing their teeth continually as they wear and break down.
A very basic piece of us—our mammalian way of
CHAPTER FOUR
TEETH EVERYWHERE
T he tooth gets short shrift in anatomy class: we spend all of five minutes on it. In the pantheon of favorite organs—I’ll leave it to each of you to make your list—teeth rarely reach the top five. Yet the little tooth contains so much of our connection to the rest of life that it is virtually impossible to understand our bodies without knowing teeth. Teeth also have special significance for me, because it was in searching for them that I first learned how to find fossils and how to run a fossil expedition.
The job of teeth is to make bigger creatures into smaller pieces. When attached to a moving jaw, teeth slice, dice, and macerate. Mouths are only so big, and teeth enable creatures to eat things that are bigger than their mouths. This is particularly true of creatures that do not have hands or claws that can shred or cut things before they get to the mouth. True, big fish tend to eat littler fish. But teeth can be the great equalizer: smaller fish can munch on bigger fish if they have good teeth. Smaller fish can use their teeth to scrape scales, feed on particles, or take out whole chunks of flesh from bigger fish.
We can learn a lot about an animal by looking at its teeth. The bumps, pits, and ridges on teeth often reflect the diet. Carnivores, such as cats, have blade-like molars to cut meat, while plant eaters have a mouth full of flatter teeth that can macerate leaves and nuts. The informational value of teeth was not lost on the anatomists of history. The French anatomist Georges Cuvier once famously boasted that he could reconstruct an animal’s entire skeleton from a single tooth. This is a little over the top, but the general point is valid; teeth are a powerful window into an animal’s lifestyle.
Human mouths reveal that we are all-purpose eaters, for we have several kinds of teeth. Our front teeth, the incisors, are flat blades specialized for cutting. The rearmost teeth, the molars, are flatter, with a distinctive pattern that can macerate plant or animal tissue. The premolars, in between, are intermediate in function between incisors and molars.
The most remarkable thing about our mouths is the precision with which we chew. Open and close your mouth: your teeth always come together in the same position, with upper and lower teeth fitting together precisely. Because the upper and lower cusps, basins, and ridges match closely, we are able to break up food with maximal efficiency. In fact, a mismatch between upper and lower teeth can shatter our teeth, and enrich our dentists.
Paleontologists find teeth wonderfully informative. Teeth are the hardest parts of our bodies, because the enamel includes a high proportion of the mineral hydroxyapatite—higher even than is found in bones. Thanks to their hardness, teeth are often the best-preserved animal part we find in the fossil record for many time periods. This is lucky; since teeth are such a great clue to an animal’s diet, the fossil record can give us a good window on how different ways of feeding came about. This is particularly true of mammal history: whereas many reptiles have similar teeth, those of mammals are distinctive. The mammal section of a typical paleontology course feels almost like Dentistry 101.
Living reptiles—crocodiles, lizards, snakes—lack much of what makes mammalian mouths unique. A crocodile’s teeth, for example, all have a similar blade-like shape; the only difference between them is that some are big and others small. Reptiles also lack the precise occlusion—the fit between upper and lower teeth—that humans and other mammals have. Also, whereas we mammals replace our teeth only once, reptiles typically receive visits from the tooth fairy for their entire lives, replacing their teeth continually as they wear and break down.
A very basic piece of us—our mammalian way of
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