In most mammals, olfaction is dominant. Smell uses a large portion of their brains, and aroma receptors are encoded by the largest family of genes. One significant neurological evolutionary change in the rise of primates has been the growing dominance of vision for millions of years. This evolutionary trajectory has left the human genome littered with now-defunct “pseudogenes” for olfactory receptors: of 853 genes for olfactory receptors, 466 are non-functioning in humans.
In spite of our evolutionary history, we are still acutely sensitive to some aromas. We can detect ethyl mercaptan, the noxious chemical added to propane to alert us to leaks, at concentrations as low as 1 part per billion (ppb), perhaps even as low as .2 ppb. That’s equivalent to three drops in an Olympic-sized swimming pool.
Japanese researchers in sanitation science (where aroma really matters) have found that we may be able to detect isoamyl mercaptan, also a sulphur-smelling compound, at concentrations as low as .77 parts per trillion. This threshold is far lower than our ability to perceive light or our sensitivity to sound.
In experiments, human olfaction can be very acute: mothers can identify their babies by smell; breast-feeding six-days-olds recognize their mothers by aroma; and in one study, subjects managed to pick out, by scent alone, their own dirty t-shirt from among a hundred others. The human sense of smell is so acute that it can detect some contaminants at concentrations lower than modern measuring equipment, for example, in recycled water bottles.
The irony, however, is that, with all this sensitivity for detection, most psychological research finds that we often struggle to identify smells. If you don’t believe it, psychologists Yeshurun and Sobel recommend that you pull jars out of the refrigerator and see how well you can identify foods blindfolded. Sobel found that even a person who ate peanut butter every day, for instance, could not identify it by smell.
Read full original article: What’s in an aroma? Languages with odor vocabularies