The sequence of 400 or so genes that control human olfaction is considered
by geneticists to be unusually diverse among animal species. Until recently,
researchers thought that any deviations resulting from that diversity led to a reduction in perception, but the results of a new sensory study have revealed otherwise.
Researchers from biopharmaceutical company deCODE Genetics conducted a two-year study on the olfactory genes of almost 12,000 people in Iceland—the largest of its kind. Based on the Sniffin’ Sticks test they administered, which involved identifying everyday smells, they found that genetic diversity does allow for enhanced olfactory ability—specifically increased
odor perception and identification.
Participants in the study smelled six odors, five of which are commonly associated with wine: licorice, cinnamon, lemon, peppermint, and banana. They were asked to name what they smelled and to rate the intensity and pleasantness of the odors; overall, peppermint was the odorant most often correctly identified, indicating that it was the strongest odor with the lowest threshold. Crucially, the study found gene variations in participants associated with the perception of licorice, cinnamon, and fish.
People with an increased sensitivity to trans-anethole—a compound found in
black-licorice products as well as botanicals such as anise seed, star anise, and
fennel—carry a gene that makes licorice odors more intense, more pleasant, and easier to name accurately. (Other studies have found this predisposition to be much more common in East Asians than it is in Europeans.) The genetic variation for cinnamon, meanwhile, influences the perception of trans-cinnamaldehyde, the major ingredient in both Chinese and Ceylon
Tasters with that predisposition find cinnamon more intense and have
lower identification thresholds, meaning they can name the odor more accurately. Fish was the sixth odor that subjects were asked to smell but the compounds responsible for salty or shellfish aromas and flavors in wine—umami, salinity, minerality, and oyster shell—can hardly be described as fishy.
For many people, however, the smell of fish can be powerful and unpleasant. Iceland’s national dish of fermented shark, known as kæstur hákar, is considered to be one of the most offensive-smelling foods consumed by humans; its fishy, blue cheese–like flavor has an ammonia-rich aftertaste that can only be described as that of urine.
This pungency is largely due to the presence of trimethylamine, a bacterial metabolite also found in animal and human secretions including semen. The synthetic version used in the study was a molecular compound of trimethylamine with the addition of small amounts of two volatile sulfur compounds. Participants who could not recognize or accurately identify it as kæstur hákar have a gene variant that results in a neutral or pleasing perception of what they may describe as rose, potato, ketchup, or caramel.
It’s safe to say that these individuals would not be able to detect high levels of volatile acidity in wine. Researchers noted that the inability to detect trimethylamine varies by population, occurring in 2.2% of Icelanders, 1.7%
of Swedes, 0.8% of Southern Europeans, and 0.2% of Africans. This sheds light on one of the many reasons why fermented shark is well tolerated by many Icelanders. The enhanced perception of cinnamon and licorice also varies by population, leading researchers to believe that the human sense of smell may still be undergoing natural selection.