By focusing on a handful of our smell receptor types, a team of scientists has demonstrated how some people are more sensitive to some smells than others. And, they have answered why we all perceive things on the ‘attractive/repugnant’ scale, differently and how this has changed as we have evolved.
Historically speaking, the new research pushes along the understanding of how, in human and primate evolution, smell came to be replaced by sight over the last few million years, something that hasn’t occurred in other species, for example dogs for which the sense of smell is still of paramount importance.
Thinking About Stinking, Scientifically
The new study was published by lead author, Dr Sijia Wang, of the Chinese Academy of Sciences, and Dr Joel Mainland of the Monell Chemical Senses Center in the journal Plos Genetics . With assistance from Unilever researchers, the new study asked 1,000 Han Chinese people to rate the ‘intensity and pleasantness’ of 10 odors on a 100-point scale. The experiment revealed two specific odor receptors: one linked with our perceptions of body odor, and another one associated with musky scents.
Even the smell of your own parents can be offensive. ( Satjawat / Adobe Stock)
The smell of body odor is caused by about 120 chemical scents, but mainly ‘galaxolide,’ a synthetic musky, and 3M2H, that carries the often offensive whiff. The research was able to identify the odor receptors involved in the detection of this scent in humans for the very first time. Also identified were receptors linked to our perception of cis-3-hexen-1-ol, that to some smells like freshly cut grass, and to androstenone, a steroid hormone that is either odorless, or smells like urine or sandalwood, depending on the genes of the smeller.
Probing The Secrets Of Olfactory Evolution
Having isolated these receptors, the scientists analyzed the whole genome of each of the 1000 participants in the trial. The study cemented previously identified perception associations, including ‘intensity, and genetic variants for specific odor receptors for three out of four of the scents, including androstenone,’ according to the paper.
The findings made in China were supported by researchers in the US. 364 participants from New York City, the majority of whom were Caucasian, were exposed to six of the odor types at various concentrations. Dr Joel Mainland, co-author of the research from the University of Pennsylvania and the Monell Chemical Senses Centre, said an ‘unusual finding’ was made. Many of the participants with two copies of a particular genetic variant for one odor receptor, were unable to smell musky galaxolide. This means only a single receptor was involved in the scent’s detection, and generally more than one receptor plays the same role.
The Future Of Smelling
Dr Mainland said scientists are still ‘surprisingly ignorant about what all the olfactory receptors do and how they interact with each other to encode olfactory percepts.’ the smell of freshly cut wild spring flowers could be called an ‘olfactory stimulation.’ The team also performed analysis of 29 mutations linked to the perception of specific odors.
This study suggested genetic variants that occurred more recently in the evolutionary history of humans and other primates are found in odor receptors ‘that appear to be less sensitive.’ Dr Mainland stressed that other receptors, or processing mechanisms, ‘may have compensated’ for a reduced sense of smell.
While it’s been suspected for a long time, now we know for sure that some people are more sensitive to certain smells than others, affecting what each of us perceive as attractive or repulsive.
This study will not only penetrate deep into the mysteries of human and primate evolution, but Dr Mainland said the new findings could have practical applications in the development of personal hygiene products. He suggested that deodorant manufacturers could, for example, home in on certain hormones and block the perception of bad smells.
Top image: Woman enjoying the scent of a flower. Source: Syda Productions / Adobe Stock
By Ashley Cowie