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Losing It: Is Our Sense of Smell Becoming Less Sensitive?
Or is science journalism getting dumber?
There were some rather alarming headlines last week. From Clare Watson at ScienceAlert.com:
“Humans’ sense of smell may indeed be gradually fading, according to a study . . . ”
From Corryn Wetzel at Smithsonian Magazine:
“Humans may be slowly losing their sense of smell, according to new study published in PLoS Genetics last week.”
From the United Press International news service:
Whoa! What’s going on? Are humans losing it smell-wise? Are we mutating into the nose-less alien from The Outer Limits?
The stories were based on a new paper in PLoS Genetics by Li et al. It compares olfactory genotype (sequence variation in odor receptor genes) to olfactory phenotype (ratings of 10 odors for pleasantness and intensity).
The study “identified novel genetic variants associated with the intensity rankings of Galaxolide and trans-3-methyl-2-hexenoic acid (3M2H).” Galaxolide is a synthetic musk to which, as Sarah Kemp and I showed, some people are odor-blind. 3M2H is a natural component of underarm odor and is the very definition of ripe BO.
But the source of the screaming headlines is Table 1 of the paper. It lists 29 SNPs (minor variants of odor receptor genes) that have been linked to the perception of a specific odor in the scientific literature. Of the 29 SNPs, 21 were linked to reduced odor perception and 11 of 13 were linked to reduced odor response in cell-based assays. Broadly speaking then, these variant odor receptor genes (“derived alleles”) are associated with lessened olfactory impact.
Thus the headlines about “fading”, “losing”, and “declining” sense of smell.
But here’s the big question: Over what time frame is this happening? Since last week? Since the Roaring Twenties? Since the Middle Ages?
Oddly enough, none of the press stories address the time frame, leaving the casual reader with the impression that nose-deadening is happening RIGHT NOW. But is this correct?
The answer is right there in Table 1. It lists the age in years of each derived allele, in other words, how long ago the genetic variant emerged. For 24 of the variants, the estimated date is more than 100,000 years ago. The 3 youngest gene variants are 84,300, 41,550, and 11,625 years old respectively.
So even if our olfactory abilities are on the skids, nothing much has happened in the last 11,000 years.
So why the alarmism? Perhaps journalists Clare Watson and Corryn Wetzel and the anonymous drone at UPI can’t be bothered to actually read the studies they report. Or perhaps they are responding to an occupational incentive to maximize clicks. [Why couldn’t it be both?—Ed.]
The Fine Print
1. “Losing” the sense of smell implies that novel gene variants that reduce the perception of odor intensity are arising more frequently in the human species, and/or that these variants are appearing in more and more people. Neither proposition is supported—or even discussed—in this paper.
2. Some share of blame goes to the authors of the study. They repeatedly use the phrase “less sensitive” when referring to smell-related genetic variations. Strictly speaking, sensitivity refers to the lowest concentration at which an odor is detectable. The paper didn’t measure odor detection levels in the test populations. It measured intensity ratings. The authors also use “less sensitive” when referring to the response of odor receptors in cell culture. This further opened the door to journalistic misinterpretation.
Full disclosure: The study cites three papers on which I am a co-author. I am personally acquainted with three of the study’s authors.
Bingjie Li, Marissa L. Kamarck, Qianqian Peng, Fei-Ling Lim, Andreas Keller, Monique A. M. Smeets, Joel D. Mainland, and Sijia Wang. (2022). From musk to body odor: Decoding olfaction through genetic variation. PLoS Genetics 18:e1009564.