Exactly how superior a dog's sense of smell is

M: While sipping on a cocktail, my Uncle Crazy was babbling scores of unproven facts when out came the claim that our best friend, the dog, has a sense of smell 200,000 times better than humans. I found this number incredibly hard to believe, but he insisted. We phoned several vets, animal clinics, nose specialists, and various 900 numbers (those were personal), and while everybody agreed that dogs have a superior sense of smell, nobody could put a number to it. We soon became extremely frustrated and tried some of our own experiments, but my dog wasn't cooperative. Please help us put this thing to rest. — Alex and Uncle Crazy, San Diego

“I’m really glad you called about this.” I was stunned. Matthew Alice hardly ever hears such a greeting. But Professor Lawrence (“Dr. Dog Nose”) Myers apparently has been poised with his hand over the phone, hoping someone would check in with just such an inquiry. Dr. Myers is the recognized expert in canine olfaction. He’s a researcher in the Institute for Biological Detection Systems in the School of Veterinary Medicine at Auburn University. They work mostly with bomb- and drug-sniffing dogs, but what he knows would apply to your unemployed pooch as well.

So, I asked, what’s the deal? Why do you read that dogs can smell 10, 150, 2000, 7000, 200,000,1 million times better than humans? Where do these numbers come from, and what’s the real answer? Says Dr. Myers, if you’re talking hard science, there is no real answer. No one has ever done a well-controlled study comparing a dog’s olfactory threshold with a human’s. We know something about what humans can smell, and we know something about dogs. But any hard numbers generated from these data are unreliable. The data for dogs and for humans were gathered under different test conditions, so they’re not comparable, except in a casual, anecdotal kind of way. And until we can teach dogs under test conditions to say, “Yes, now I can smell that,” we will probably never have a reliable number. Scent threshold in dogs is measured by inference from behavior or EEG readings.

Olfaction is to dogs what vision is to humans. It’s their memory system, their primary sense in dealing with the world. As you might expect, then, the physiology of a dog’s smeller is much larger and more complex than ours. Dogs have 20 times more scent receptor cells than humans, and the scent-processing section of their brains is larger. Where we might say, “Mmmm — burgers!” a dog would say, “Mmmm — fried ground cow muscle, gristle, and fat; soy extender; imitation American cheese made with vegetable oil and dry milk; wheat bun, toasted; a dozen sesame seeds; one leaf day-old lettuce; raw, partly green tomato slice; vinegar and spices in a tomato-based sauce, all touched by the hands of a human that I know and who will give me some if I make a big enough pest of myself.” Dogs smell in minute detail. How do we quantify that?

And certain breeds of dogs are naturally better smellers. Pointers, bloodhounds and most other hounds, some terriers. But you can take almost any dog and train him to discriminate more keenly than he does naturally. And you can breed a super-keen olfactory sense into a line of dogs, as has been done with some gun dogs and hunters. How do we quantify that?

There’s also the technical problem of reducing the scent stimulus to small enough quantities to get reliable readings. Dr. Myers doesn’t deal in parts per million of an odor, he’s usually talking about parts per trillion or quintillion. In some cases, the dog’s nose is sharper than the technology. Other variables are the type of odor, air temperature and humidity, and the physiological condition of the dog (or human).

Dr. Myers has been quoted as saying dogs can smell a million times better than humans. He says that was a speculative (but possible) number he used in an interview to illustrate a narrow point. The reporter picked up the figure as science and quoted it out of proper context. So where does this leave you and Uncle Crazy? Guess you’re both wrong and both right, depending on the dog, the human, the odor, the circumstances. Nobody, not even Dr. Myers, can prove otherwise.

But hey, Uncle Crazy, I just read that a scientist in Michigan has discovered that the best smellers in the world are fish. A thousand times better than dogs, he says. Lay that one on Alex at cocktail time and see what he says.