Consider the dogs. Dogs don’t groom each other to the same extent that apes do, so there’s no reason to expect that they would try to examine a mark on their heads. What’s more, the mirror test is a visual test, designed by visual animals (us) for other visual animals. Dogs see just fine, but they mainly live in a world of smell. If you want to know if they have a concept of self, it makes little sense to confront them with a mirror. You need to work in their world. A world of chemicals drifting through the air. A world that’s hard for us to imagine.
“Smell is so distant to our experience,” says Alexandra Horowitz from Barnard College. “We’re just not engaged with olfaction, so it’s taken a long time to see—or even imagine—what the world might be like for non-visual creatures, and to design experiments with that in mind.”
Marc Bekoff from the University of Colorado, Boulder, did just that with his own dog Jethro. Over five winters, he would scoop up snow that Jethro and other dogs had peed upon, and move it to new locations. “For some reasons passers-by thought I was strange and generally left me alone,” Bekoff later wrote. He found that Jethro spent less time sniffing his own urine than that of other dogs. He wouldn’t have been able to recognize himself in a mirror, but he could recognize his own distinct odor.
Inspired by this “yellow snow experiment,” Horowitz (who once studied with Bekoff) designed a bigger and more thorough study. She recruited 36 New York dog owners and presented their pooches with two canisters. In one, she put a tiny drop of each dog’s own urine. In the other, she put the same urine along with a different scent—the equivalent of marking an animal’s head with red dye.
The dogs spent more time sniffing the canister with the modified odor than the one with their unadulterated urine. The presence of the extra scent changed how they behaved toward their own smell, just as the presence of a red mark changes how a chimp behaves toward its image in a mirror.
Does this mean that they’re recognizing their own olfactory “reflection”? Not quite. Horowitz also gave the animals a choice between their adulterated urine, and the adulterating smell on its own. And this time, they sniffed both canisters just as often. This suggests that the dogs were drawn to the modified urine not because it contradicted some sense of self, but simply because it was unfamiliar. Dogs, after all, are drawn to new things.
After seeing these results, Horowitz wondered if she had made her life more difficult than necessary, by choosing a scent that was too powerful. She had adulterated the dogs’ urine with an extract of cancerous tissue, taken from a dog at a nearby veterinary school. Perhaps that was just too interesting a scent.
To control for this possibility, Horowitz repeated her experiment with 12 new dogs. This time, she altered their urine with a more neutral odor—anise essential oil. Once again, they spent more time sniffing their urine when it had been modified. But this time, they also sniffed that modified urine more than a sample of anise oil on its own. “I think it’s a nice analogy to the chimpanzee seeing a red mark on her forehead,” Horowitz says. “Seeing a red mark isn’t intrinsically interesting. It’s only interesting when it’s situated on oneself.”