The narwhal is an odontocete or toothed whale, but unlike all other toothed whales it has no teeth in its mouth. Instead, the male develops a long straight tooth (or tusk) that protrudes 2-3 m out of the upper left jaw. The tooth grows in a counterclockwise spiral. The tusk is unique to male narwhals. Very rarely, a female will grow a tusk, or a narwhal will grow two tusks. Tusks exported from the Arctic, perhaps by the Vikings, reached Europe, the Mediterranean, and even the Far East as early as the Middle Ages and became the source of the unicorn myth. The tusks were sold without a good description of the animal from which they came and inspired a great deal of fantasy.

To some extent, the tusks still inspire fantasies, as many explanations have been proposed for the purpose of the tusk, including: breaking ice, swordfighting, spearing fish for food, or for digging in the bottom the sea. In fact, none of these behaviors have ever been observed. One thing that is clear, is that the tusk can not serve a critical function for narwhals’ survival because females, who do not have tusks, still manage to live longer than males and occur in the same areas while additionally being responsible for reproduction and calf rearing.

The scientific consensus is that the narwhal tusk is a sexual trait, much like the antlers of a stag, the mane of a lion or the feathers of a peacock. Males use the tusk to determine social rank and compete for females. During the summertime in the northern Canadian high Arctic bays and fjords (long narrow inlets), male narwhals can be seen carefully crossing their tusks and making a strange, sad whistle. There is often a female between them. Such behavior might help maintain dominance hierarchies or help young males develop skills necessary for performance in adult sexual roles.

The sexual selection theory was originally proposed by Charles Darwin in his theories of sexual selection in his book The Descent of Man, and Selection in Relation to Sex (1871). Darwin makes the case very succinctly:

“When the males are provided with weapons which the females do not possess, there can hardly be a doubt that they … have been acquired through sexual selection.”

This observation echoes one made by the arctic explorer William Scoresby in his book: An Account of the Arctic Regions with a History and Description of the Northern Whale-Fishery (1820). Because his observations stand up to modern scientific scrutiny, I’d like to offer the following complete quote: