Friday, May 20, 2011

The Narwhal Tusk Debate

            Numerous theories have been presented over the centuries to explain the function or purpose of the narwhal tusk, the strangest tooth in nature: as a spear for hunting or a tool for digging, as a weapon of defense or aggression, an instrument for breaking ice or sound propagation, or even as a swimming rudder or an organ for breathing.
Photo by Paul Nicklen

If you search the Internet for an answer, most of the results will be somewhat misleading. The answer you will no doubt find there is that the tusk is a sensory organ that the whale uses to somehow sense something about its environment.  That’s the conclusion of a Connecticut dentist, Martin Nweeia, who has done a great deal of study of the tusk.  But almost all of the narwhal biologists on the planet disagree.  Vehemently.  Yet the media picked up on Nweeia’s announcement of his findings and it raced around the Internet, much to the chagrin of the biologists. The sensory organ conclusion has found its way into natural history museum exhibits, award winning books, and respected publications around the world, yet even Nweeia would agree that he hasn’t amassed the scientific proof of his hypothesis.
The biologists, on the other hand, all stake their reputations on their belief that the narwhal tusk – the male whale’s left tooth, which spirals out to a length of up to eight feet -- is a “secondary sexual characteristic,” like the antlers on a deer, the tail of a peacock, and the mane of a lion.  It’s a physical adornment designed to attract a mate and demonstrate dominance over other males, they say. If it were important for sensing their environment, females would have one, too. (A tiny percentage of females do.) The scientists point to Charles Darwin, who argued in 1871 that “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.” Half a century before Darwin, Arctic explorer William Scoresby concluded similarly: “It cannot be essential for procuring their food, or none of them would be without it: nor is it, perhaps, necessary for their defense, else the females and young would be subjected to the power of enemies without the means of resistance, while the male would be in possession of an admirable weapon for its protection.”
I’ve interviewed all of the parties involved, and all are passionate about their position.  Perhaps the harshest critic of the sensory organ theory is biologist James Finley, who wrote to me in an email, “The romance of the narwhal makes people want to fantasize all sorts of bizarre function.  Nweeia is dreaming. It continues to amaze me that practically every account of the narwhal, even some by biologists, has to end with the assertion that we still don’t know the function of the mysterious narwhal tusk. It’s no more mysterious than a moose’s antlers, yet we are loath to let the legend die.”
Nweeia’s conclusion is based on his finding that the tusk has millions of tiny tubules extending from the inner core of the tooth to the outer edge, unlike in any other mammalian tooth, enabling seawater to penetrate to the nerve endings in the tusk. From that finding, he drew his hypothesis about it being a sensory organ, and he has been working to prove it ever since by administering water of varying salinity levels to the tusk of live narwhals and observing their physiological reactions. It has taken five or six years of effort to get results from half a dozen animals, and he is convinced he is right. But he hasn’t published his results, so none of the biologists have been able to review his claim.
So the debate goes on. Though to call it a debate is overstating the situation, because – unlike most scientific debates – those on either side of the question have never communicated with each other.  It’s a stand-off with no end in sight. 

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