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Was It Designed?

The Sea Urchin’s Self-Sharpening Tooth

● Using its five teeth, the sea urchin bores through rock to carve out a niche in which to hide. Despite the grinding and scraping, the urchin’s teeth stay sharp. “That’s far more than we can say about any cutting or grinding tool we know and use,” says Pupa Gilbert, professor of physics at the University of Wisconsin–Madison in the United States. What is the sea urchin’s secret?

Consider: A sea urchin’s tooth is composed of crystals that are cemented together. However, “there are breaking points at predetermined locations built into the teeth,” notes Gilbert. The weaker organic material at these locations—like perforations on a sheet of paper—make it easy for the tooth’s worn layers to shear off, exposing a new, sharp edge. Since the tooth keeps growing at one end and self-sharpens at the other end, it never gets dull. Gilbert calls the urchin’s tooth “one of the very few structures in nature that self-sharpen.”

Knowing how the sea urchin’s self-sharpening tooth works has exciting implications for toolmakers. In theory, it could lead to the development of tools that self-sharpen with use. “The mechanism used by the urchin is the key,” says Gilbert.

What do you think? Did the sea urchin’s self-sharpening tooth come about by chance? Or was it designed?

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Growing tooth

Calcareous plate

Sharpened tooth

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Sea urchin

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Five teeth

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Both photos: Courtesy of Pupa Gilbert/University of Wisconsin-Madison