True to legend, a bloodhound can track someone for miles just by keeping its nose to the ground; that proximity makes it all the easier to smell foot sweat. Akin to a molecular thumbprint, sweat is a cocktail of different odorants, and bloodhounds are particularly adept at discerning the unique mixture of isobutyric acid and isovaleric acid molecules. Their sensitive noses have olfactory acuity that is 100 to 1,000 times greater than humans.
Nearly all mammals have a more sensitive sense of smell than humans. In rats, for instance, smell is almost equivalent to face recognition in people, says neurobiologist Larry Katz from Duke University. Simply by smell, he says, they can tell whether another rat is male or female, from the same family or another species.
The sense of smell has long been known to influence behavior in animals and humans, but scientists couldn't access the olfactory system's inner workings to find out how. Then, in 1991, molecular biologist Linda Buck, then at Columbia University, New York (now at Harvard Medical School), and then-colleague molecular biologist Richard Axel, cloned a large family of odor receptor proteins. (1) This work allowed researchers to begin deciphering the olfactory code--a discovery that would lead to understanding how the brain knows what the nose smells, and ultimately how odors influence behavior. Researchers are now applying various methods from molecular biology, neurobiology, neuroanatomy, psychology, and other fields in hopes of attaining these goals.
"Ten years ago, the field was practically a backwater, and then Buck and Axel discovered the olfactory receptors," says Katz. "That broke the field open and put it on firm molecular footing, attracting a lot of people into the field. Today, olfaction is a field that's truly exploding." …