What the Nose Knows - Avery Gilbert [30]
So, yes, dogs can smell odors associated with bladder cancer. But this is a far cry from “What’s that, Lassie? Timmy has bladder cancer?” To make use of this canine talent, your local hospital would have to maintain a half-dozen dogs and their trainers, supply copious medically certified human urine samples, and provide ongoing statistical support and chemical analysis. At which point six out of ten bladder cancers would go undetected.
If the human nose received the same gee-whiz treatment given to animal stories, we would sound as impressive as any dog. Here’s an example: Just by smelling some ice cream that once had a wooden popsicle stick in it, regular folks can tell whether the stick came from Wisconsin, Maine, British Columbia, or China. Amazing, no? How do those monkey-people do it? In this case, wooden sticks from each locality were frozen in vanilla ice cream for six days. The samples were melted and the sticks removed. The sniffing primates—Ohio State graduate students—had to pick the same sample from a repeatedly presented pair of samples five times in a row to be declared a success. All possible pairs of wood source were tested. Two judges failed—they couldn’t tell one stick-scented ice cream from another. Eight judges succeeded—they could reliably discriminate anywhere from five to nine of the ten possible pairings. Not bad for humans. Could the judges explain how they did it? Unfortunately not, but then, neither could the cancer-sniffing dogs.
The physicist Richard Feynman had a great party trick in which he would identify by smell objects briefly handled by other guests when he wasn’t looking. He said it was easy to do because peoples’ hands have surprisingly different scents. (A 1977 study confirmed that hand odor is individually distinctive and discriminable.) There are other stupid human tricks besides Feynman’s. For example, in a lineup of dirty laundry we can pick out the T-shirt worn by our spouse or partner. A mother can identify the smell of her own baby, and a baby can pick out the scent of its mother’s breast.
How do humans measure up at the quintessential doggy task—scent tracking? Researchers at UC Berkeley had people get on their hands and knees and follow a 10-meter-long chocolate-scented trail using only their noses. The test subjects wore goggles, gloves, and kneepads, which restricted nonolfactory input. Two-thirds of the people tested successfully followed the trail under these conditions. (When subjects wore nose plugs, none of them could follow the trail.) With a few days of training, tracking speed was doubled and people strayed less from the scent trail. Dog lovers (of which I am one) may also be surprised to learn that drug dogs and humans have almost identical sensitivity to methyl benzoate, the smell used to track cocaine. Dogs have great noses, but it’s time to stop the trash talk and give ourselves more credit.
Many people take it for granted that the human nose is inferior, and scientists often make the same assumption. Charles Darwin thought our evolutionary ancestors made good use of smell, but felt it was “of extremely slight service, if any” to modern man. The sex psychologist Havelock Ellis agreed: “Among the apes it has greatly lost importance and in man it has become almost rudimentary, giving place to the supremacy of vision.” The