Decoding Our Sense of Smell
Scientifically speaking, all of the fragrances and stinky stuff we smell are chemicals known as odorants, each of which is composed of many molecules. One modification in the chemical structure of an odorant can completely alter its smell. “A slight change in the chemistry of orange scent and you get something that smells like sweaty socks,” says Buck. She and Axel found that the process by which we identify smells begins with 350 olfactory receptors in a patch of cells at the top of the nasal cavity known as the olfactory epithelium. These tiny receptors snatch up separate bits and pieces of arriving odorants.
But how do 350 receptors sort out all the millions of molecules that make up the more than 10,000 different odors we recognize? The combined efforts of a number of different receptors are needed to identify a single odor, such as ozone during a summer thunderstorm, or the steamy scent of rain on sun-heated asphalt. Once a receptor picks up a molecule from that incoming odorant, it sends out an electrical signal containing the chemical information it has captured to the olfactory bulb, a plum-sized relay station located in the brain. From there, the signal is dispatched to the brain’s cortex, where all of the information from the receptors is combined, allowing us to recognize that “eau de summer storm.” Exactly how this last phase happens, though, has yet to be unraveled.
Aromas of Attraction
Smell may play a big role in how women choose their mates (men, no surprise, focus more on outward sex appeal). “Women are first attracted to a man visually and then by how agreeable he is. But when they become more intimate, smell becomes a factor,” says Rachel Herz, PhD, a Brown University researcher who studies smell and behavior.
There’s a sociobiological reason for this that harks back to women’s evolutionary need to find a mate who is genetically compatible so that they can have healthy children. We know that humans have odor prints as distinctive as their fingerprints (just ask a bloodhound or a woman who sleeps with her husband’s T-shirt when he’s away from home). These odors “may be a special signal to tell a woman that a man’s genes are similar enough for compatibility but different enough to have a healthy child,” says Herz.