A Biological Mystery Solved
I've always been fascinated by things Arctic; I've read Barry Lopez and John McPhee with great enjoyment. Lopez in particular wrote pretty extensively on a scientific mystery of the narwhal's tusk, an eight-to-ten foot spiraled tooth jutting from the mammal's head. Represented historically as a unicorn's horn, the narwhal's tusk played a significant role in the symbolism of early modern kingship (according to Lopez, Christian V of Denmark was crowned in 1671 in a throne made of narwhal tusks).
But what is a narwhal's tusk for? The question has bedeviled scientists for several hundred years. Was the tusk a defensive weapon? Hunting tool? Echolocator? Sound producing device? (Or, Herman Melville suggested sarcastically, a letter opener?) Not all narwhals have tusks though, which seems to rule out a function necessary to survival.
A professor at the Harvard School of Dental Medicine now claims to have solved the problem:
[Martin] Nweeia has discovered that the narwhal's tooth has hydrodynamic sensor capabilities. Ten million tiny nerve connections tunnel their way from the central nerve of the narwhal tusk to its outer surface. Though seemingly rigid and hard, the tusk is like a membrane with an extremely sensitive surface, capable of detecting changes in water temperature, pressure, and particle gradients. Because these whales can detect particle gradients in water, they are capable of discerning the salinity of the water, which could help them survive in their Arctic ice environment. It also allows the whales to detect water particles characteristic of the fish that constitute their diet. There is no comparison in nature and certainly none more unique in tooth form, expression, and functional adaptation.Startling, indeed, and more interesting than even Melville's thoughts about the uses to which the narwhal puts its tusk!
"Why would a tusk break the rules of normal development by expressing millions of sensory pathways that connect its nervous system to the frigid arctic environment?" says Nweeia. "Such a finding is startling and indeed surprised all of us who discovered it."
(Seee Barry Lopez, Arctic Dreams (Vintage, 1986), 142-148. Lopez also wrote another wonderful book, Of Wolves and Men.)