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The most broadly accepted theory for the role of the tusk is as a secondary sexual characteristic, similar to the mane of a lion or the tail feathers of a peacock. This hypothesis was notably discussed and defended at length by Charles Darwin, in The Descent of Man, and Selection in Relation to Sex (1871). It may help determine social rank, maintain dominance hierarchies or help young males develop skills necessary for performance in adult sexual roles. Narwhals have rarely been observed using their tusk for fighting, other aggressive behavior or for breaking sea ice in their Arctic habitat.
