The narwhal’s giant unicorn horn might help them find mates
I like big tusks and I cannot lie.
When you’re in the dating game, sometimes you develop a type. Maybe it’s someone tall, or funny, or with a particular hair color. Perhaps you’ve always had a bit of a soft spot for animal lovers, musicians, or dorky types. But humans aren’t the only ones who find certain characteristics attractive. According to a new study in Biology Letters, narwhal ladies have a type too—and it’s all about the tusk. The study’s authors hypothesize that males having a disproportionately giant tooth, which kind of looks like a unicorn horn, signals to females that they would be an excellent choice for a partner. It also tells other males that they are a big tough guy.
The study authors collected information from 245 adult male narwhal skeletons from across the world, gathered over 35 years. Because the tusks were so large compared to the rest of their bodies, and the fact that the giant tooth-like appendages’ sizes varied considerably among the group, the scientists proposed that the tusks are sexually selected—and that their primary purpose is essentially narwhal sex appeal.
Sexual selection is a key component of natural selection. Certain features evolve because it makes critters appear to be a more attractive partner or person to reproduce with, which can lead to crazy traits like a peacock’s feathers or the antlers of an elk, says study author Zack Graham, a fourth-year animal behavior Ph.D. student at Arizona State University.
The narwhal’s tusk, which is essentially just a giant, swirly fang, grows disproportionately to the animal’s body size. So a bigger narwhal doesn’t necessarily have a larger tusk than a smaller narwhal— all “horns” grow at a different rate. This is one of the key features of sexually selected traits, says Graham.
Male narwhals size each other up based on tusk length, says Graham, but they don’t reach a full-on joust, which would likely end in death for one of the battling narwhals.“They definitely engage in aggression,” he says. “But they’re not ramming towards each other.”
Plus, just like teeth, the tusks aren’t self-repairing, and once a narwhal has broken their’s, it’s gone for good.
Martin Nweeia, a narwhal expert and researcher at Harvard, isn’t quite convinced that the size of the animals’ tusks plays a role in sexual selection. He also doesn’t necessarily agree that male narwhals show aggression enough to warrant thinking that their tusks are built for aggression. Earlier research, dating back to the 1920s, has recorded very little of this kind of male aggression. The Inuit hunters Nweeia has worked with say they have rarely captured anything besides an incidental tussle.
“Nobody’s backing this aggression thing up,” he says.
Not to mention, not all male narwhals even have tusks. The largest specimens tend to not have them, Nweeia says, and it’s not a rarity for females to have a tusk. Around 15 percent of lady narwhals will have one, which is more common than left-handedness in humans. Some narwhals, both male and female, can even have two husks. So, the whole idea of sexual selection is more complex than the bigger the better.
“You’ve got a more complicated expression that is not being included in the dataset,” Nweeia says.
Nweeia’s prior research proved that the husks can also act as a sensory organ. When the tusk interacted with different chemicals, the creatures’ heart rates changed. He argues that the tusks have purposes beyond being used to battle it out with competing males. Saying that would be like arguing humans mostly use their teeth to fight each other, instead of discussing their more common other uses.
So are big tusks sexy tusks? Maybe, but they’re probably doing more than just creating a dreamy unicorn aesthetic or a built-in spear, and it’s not only the boys who get to have all the giant-toothed fun.
