The Spiral in the Tusk of the Narwhal

Abstract

The spiral in the tusk of the narwhal (Monodon monoceros ) has been fanciful ly, but never satisfactorily, explained. Spiral growths are common in the animal kingdom and share the feature of having straight axes. A curved tusk would hinder the narwhal swimming; a spiral mode of growth ensures overall straightness even if the tusk grows irregularly. The need to keep the tusk straight completely and satisfactorily explains the spiral.