In the late 1980s, an Inuit subsistence hunter named Jens Larsen killed a trio of very strange whales off the western coast of Greenland.
He and his fellow subsistence hunters would regularly catch two species: narwhals, whose males famously have long, helical tusks protruding from their snouts; and belugas, with their distinctive white skin. But Larsen’s new kills were neither. Their skin wasn’t white, nor mottled like a narwhal’s, but uniformly grey. The flippers were beluga-like, but the tails were narwhal-esque. In all his years of hunting, Larsen had never seen anything like them. He was so struck that he kept one of their skulls on the roof of his toolshed.
In 1990, it caught the attention of Mads Peter Heide-Jørgensen, a scientist who studies marine mammals. With Larsen’s permission, he took it to the Greenland Fisheries Research Institute in Copenhagen for study. And after comparing it to the skulls of known belugas and narwhals, he suggested that it might have been a hybrid between the two species—a narluga.
It was a reasonable idea. Belugas and narwhals are the same size, share the same Arctic waters, and are more closely related to each other than to any other species. Individuals from both species have been found swimming among each other’s pods. But no one had ever found a narluga before, and at the time, Heide-Jørgensen had no way of confirming his hypothesis.
That changed in the intervening decades, as researchers developed more and more powerful ways of yanking minuscule amounts of DNA from bones. These techniques have typically been used to study ancient creatures such as Neanderthals and mammoths. And now they have helped to prove that the narluga is indeed a narluga, supplying the first genetic evidence that such creatures even exist.
By analyzing DNA extracted from one of the creature’s teeth, a team led by Eline Lorenzen from the Natural History Museum of Denmark showed that it was a male, born to a beluga father and a narwhal mother. Most of its DNA was a half-and-half mix between the two species, but its mitochondrial DNA—a secondary set that animals inherit only from their mothers—was entirely narwhal. “A while back, we presented our findings at a conference of 150 people who are very into belugas, and you could hear a pin drop,” Lorenzen says. “None of them were familiar with hybrids between those two species.”
A brief digression: When naming hybrid animals, patriarchal conventions dictate that the father’s species comes first in the portmanteau. A cub born to a male polar bear and a female grizzly is a pizzly, but one with a grizzly dad and a polar mom is a grolar. So, technically, the skull from Larsen’s toolshed is a belwhal, not a narluga. But the latter name might well stick because it’s been called that for decades and, as Lorenzen says, narluga just sounds better.
Narwhals and belugas have been evolving independently for at least 1 million years. They clearly can still breed with each other, but no one knows why or how often that happens. Both species breed at a time of year when thick sea ice keeps inquisitive scientists out, so we know next to nothing about how they reproduce. The male narwhal’s tusk, for example, was thought to be so sexually attractive that a female narwhal would be unlikely to mate with a tuskless male from another species. And yet, the narluga’s narwhal mother clearly did have sex with a beluga. “What are the odds that someone would find the only hybrid ever and keep it on his shed, and that someone else would find that and send it to a museum?” Lorenzen says. “There must be more. But maybe not! We have no idea.”
The strangest part of the narluga’s skull is its teeth. Belugas have up to 40 teeth in their upper and lower jaws, all of which are identical. Narwhals have no teeth at all, besides the spiraling tusk and a pair of vestigial teeth behind it. The narluga seemingly split the difference between its parents with 18 teeth, all different and strangely shaped. Many of these stuck out horizontally, and some even had spirals that turned in the same direction as a narwhal’s tusk. It’s as if someone took the program for creating a narwhal tusk and ran it in a beluga’s mouth.
By analyzing the chemical composition of those weird teeth, Lorenzen’s team could work out what kind of food the narluga ate. And they showed that its diet must have been radically different from either of its parents, both of which dive in search of fish and squid. The narluga’s teeth, by contrast, were chemically closer to bottom-feeders like walruses, which dig up buried prey from the ocean floor. Perhaps the narluga did the same thing, using its outwardly protruding teeth as shovels for rootling through sand.
There’s something faintly magical about that. This fluky merger between two species ended up with a mouth that doesn’t normally exist in nature but still found a way of using it. It lived neither like a beluga nor a narwhal, but it lived nonetheless.
But there’s a dark side to hybridization, especially for the Arctic’s endangered residents. If hybrids are infertile, as they often are, they would act as genetic dead ends for already small populations. If they are fertile, the mixed genomes of their offspring could displace those of their respective parents. As the Arctic warms and its ice disappears, some scientists are concerned that once-isolated species could be meeting and mating more frequently, and damaging their own prospects in the process.
Does the narluga “represent an isolated event, or does it signal an increase in hybridization as a consequence of changing climates?” asks Sandra Talbot from the United States Geological Survey. And if it’s the latter, does cross-breeding offer a way for narwhals to bolster their relatively low levels of genetic diversity by bringing in genes from their closest relatives, or might it inadvertently doom them?
Modern humans still carry the genes of Neanderthals, Denisovans, and our other ancient relatives, but those groups are all extinct now. If polar bears and narwhals get edged out in a world of pizzlies and narlugas, they could suffer the same fate.