The Truth About the Tooth

Exploring the secrets of the narwhals' mysterious horn

• Hannah Schardt
• Apr 01, 2006

FOR CENTURIES, the nine-foot-long tusk of the narwhal has been a source of fascination--and a desirable trophy--for humans. But until recently, no one knew what purpose the tusk served for the narwhal to which it was attached. Was it for poking holes in the ice? For fighting? For impressing the opposite sex? New research suggests a different answer: None of the above. A group led by Martin Nweeia, a dentist and researcher at Harvard School of Dental Medicine, has discovered that the tusk may be a delicate instrument that can detect even slight changes in the environment.

Unlike every other tooth known to science, the spiral tusks, which grow singly out of the jaws of most male and some female narwhals, are dense at the core and softer on the surface. Braving icy Arctic waves, Nweeia subjected the tusks of several narwhals--briefly held captive for tagging--to changes in salinity and temperature while observing the animals' brain activity with electrodes. He found that the narwhals' brains reacted noticeably to the changes. Nweeia plans to continue his study to find out why an animal that lives in frigid waters would benefit from such a sensitive tooth. "Nature has done all kinds of odd things," he says, "but as far as teeth go, this is by far the oddest."