A surprising new study suggests that people can track a scent across a grassy field--at least if they're willing to get down on their hands and knees and put their noses to the ground. The findings are unlikely to put hunting hounds and drug sniffing dogs out of work, but they may earn a little respect for the poorly regarded human sense of smell.
Humans are widely believed to be poor at tracking scents, especially when compared to other mammals such as dogs and rodents. But few had ever put that idea to the test. A research team led by Jess Porter and Noam Sobel at the University of California, Berkeley, dipped 10 meters of twine in chocolate essence and laid it in a field to form two straight lines connected at a 135° angle. Then they blindfolded 32 undergraduate students and had them don earmuffs, thick gloves and kneepads to prevent them from using sensory cues other than smell. When set loose in the field, two-thirds of the subjects successfully followed the scent, zigzagging back and forth across the path like a dog tracking a pheasant, the researchers report online 17 December in Nature Neuroscience.
Nearly all the subjects reported that the task was challenging, Porter says, but four of them got a chance to improve with practice. Over the course of several days, they learned to follow the trail faster and deviate less. Even so, their performance remained well below what other researchers have reported in dogs. Additional experiments with noseplugs suggested that people use two strategies to localize smells: comparing the odor intensity between subsequent sniffs and comparing the odor intensity at the two nostrils during single sniffs.
"This is an innovative approach to teasing out what olfactory abilities humans actually have," says Gordon Shepherd, a neuroscientist at Yale University. It's assumed that after our primate ancestors started walking on two legs, their sense of smell became less acute, Shepherd says. The relatively small repertoire of olfactory receptor genes in primates compared to animals that kept their noses closer to the ground seems to support this notion. However, Shepherd says, the new study suggests that "if we go back on our four legs and get down on the ground, we may be able do things we had no idea we could do."