In Remembrance of Things Past, Marcel Proust dwells on the deep, emotional recollections that scents can trigger. Such memories turn out to have a biological basis. Unlike other senses, our sense of smell has a direct line to the emotional center of the brain; the olfactory bulbs protrude into its limbic region.
Some sensations associated with odors are tactile, not olfactory. The burn of hot pepper, the soothing coolness of menthol, and the tear-inducing sting of chopped onion all result from irritation of the trigeminal nerve system, which senses pain and temperature in the nose and face.
Human sperm have odor receptors, suggesting that sperm may locate ova by scent.
Humans have approximately a thousand different odor receptors corresponding to different genes, roughly 35 percent of which are active. In canines, 85 percent of olfactory receptor genes function, accounting for dogs’ superior sense of smell.
Although our preferences for aromas are weighted by experience, there’s evidence that they are, in part, genetic. Identical twins tend to share the same opinion of the polarizing scent of cilantro, whereas fraternal twins’ predilections often differ.