Elephants have five times more olfactory receptors than humans and the most of any animal characterized to date, according to a new study. (Courtesy of Eric Green)

Elephant noses might be the most discerning mammalian sniffers on the planet. According to a new study published Tuesday in Genome Research, African elephants may best humans, mice and even dogs on the measure of olfactory receptor genes.

But that doesn’t mean elephants should replace canines on a police squad. While the number of active olfactory genes in elephants is quite impressive — 2,000, which is twice the number found in dogs and five times the number found in humans — scientists say there isn’t a clear connection between having more genes and being a better smeller in every way. It’s not all about the number of olfactory receptor genes but also how an animal uses them.

“We don’t really know how the number of olfactory receptor genes relates to olfactory ability,” said study author Yoshihito Niimura, a researcher at the University of Tokyo’s department of applied biological chemistry. “For example, dogs are known for their keen sense of smell — but we actually already knew that their number of genes was much smaller than mice, who we don’t see with that same ability.” Dogs, Niimura said, have very sensitive noses but perhaps less discerning ones.

“Dogs are very good at smelling particular odors,” he said, “like the smell of humans. They can detect those odor molecules even at very low concentrations,” which is why they can follow the trail of a scent they pick up. “In that sense,” he said, “a dog has a sense of smell that’s something like a million times better than a human’s,” and certainly better than an elephant’s as well.

The advantage for elephants, Niimura said, most likely lies in a broader range of identifiable smells. Previous studies have indicated that Asian elephants are able to distinguish between very similar odor molecules — ones that humans and other primates find impossible to separate.

Indian elephant Rhena drinks from a water hose at the zoo in Krefeld, Germany. (Roland Weihrauch/European Pressphoto Agency)

This is useful to the creatures in several ways: Elephants can recognize other elephants by the smell of their urine, and research suggests that some elephants also use pheromones — smelly chemical signals that animals use both to communicate with and to induce involuntary reactions, like arousal, in other members of their species.

It’s not surprising that elephants have become so reliant on olfaction, Niimura said. They use their trunks to interact with the world. “Imagine having a nose on the palm of your hand,” he said. “Every time you touch something, you smell it.” So whether foraging for food or greeting a friend, elephants put their nose to the test. And African elephants use their sharp sense of smell to deal with humans, too.

“In Kenya, anecdotally, everyone knows that wild elephants are able to distinguish one tribe from another,” Niimura said. A 2007 Current Biology study examined this phenomenon: Elephants were found to react aggressively to both the colors and smells of the Maasai tribe, which spears elephants to show courage and strength. Signs of the Kamba tribe, which doesn’t hunt elephants, didn’t seem to bother them. “There’s certainly an indication,” Niimura said, “that we’re seeing their ability to distinguish odors there.”

So the cliche of the never-forgetful elephant may have something to do with their killer olfaction, which could help them distinguish places and people from one another. “But I must make a point of saying,” Niimura said, “that elephants are very intelligent.” Not all credit can be given to a good nose, but elephants also seem adept at turning those smells into useful knowledge.