New Study Confirms the Human Sense of Smell Is Fading

Are we really on the verge of losing our sense of smell or just out of practice?

In a recent study led by Bingjie Li of Shanghai Institute of Nutrition and Health, 1364 participants were asked to smell ten different scents.

The participants comprised of 1,000 Han Chinese people and 364 ethnically diverse people from New York.

The participants were asked to rate ‘the intensity and pleasantness of the odors on a 100-point scale‘.

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The researchers compared the participants’ responses with genetic variations of the participants’ olfactory genes. The researchers hoped to find links between genes and how people perceive scents.

What are olfactory genes?

Wikipedia defines olfactory genes as; olfactory receptors trigger nerve impulses which transmit information about odor to the brain.  Olfactory receptors form a multigene family consisting of around 800 genes in humans.’

olfactory nose

Humans have considerably fewer olfactory genes/receptors compared to other animals. Animals that have a more powerful sense of smell compared to humans have many more olfactory receptors.

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Scientists guess the dog’s sense of smell is somewhere between 10,000 to 100,000 times more acute than ours. One of the reasons a dog has such better smelling ability than us is the number of scent receptors. For every scent receptor, a human has, a dog has about 50.

Two scents of scientific interest, Galaxolide and 3M2H

The scents used in the study included two odors that people often perceive differently or not at all.’. The two scents that the study focused on were Galaxolide and 3M2H.

Galaxolide is a synthetic musk with a clean sweet musky floral woody odor used in fragrances.

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3M2H, an abbreviation for trans-3-Methyl-2-hexenoic acid, is a ‘key molecule associated with body odor from human underarms.’

The study included Galaxolide and 3M2H because the team had discovered two new smell receptors: one that senses Galaxolide and the other that senses 3M2H.

People would experience the strength of the scents of Galaxolide and 3M2H very differently depending on their gene mutations in these two newly discovered receptors.

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The study also looked at another 27 known odor-related mutations.  The study examined theevolutionary age of when each mutation slipped into our genomes and whether the changes were thought to make human smell receptors less or more sensitive to smells.’  

Findings of the study

What the scientists found supports what they say is ‘a long-standing hypothesis that human sense of smell may have degraded over time due to changes in the genes that encode our smell receptors.’

In summary it seems our smell receptors have evolved to become less sensitive over time.

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If Darwin were alive today, you might wonder what he would think about people evolving to have a less sensitive sense of smell and how this latest research would sit with his theories of natural selection. Natural selection is a theory that people inherit characteristics that increase the chance of survival. Do people have a better chance of surviving and finding a mate if they have developed a less sensitive sense of smell over time?

Other commentators on this research have suggested that eyesight has become our dominant sense.

Majid from Radboud University commented that the findings of this study are not accurate because the sample population was taken from ‘Western participants, who live in a culture where olfaction is not particularly elaborated.’

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Majid says, “people in other parts of the world are better at odor detection, discrimination, and naming, such as the Jahai people of Malaysia.”

Our sense of smell or lack of it for noticing body odor from human underarms certainly makes for an exciting discussion. Sadly humans are very far behind the animal kingdom when it comes to our ability to smell, A male luna moth can detect the scent of a female from over six miles away!‘ We have evolved not to require a strong sense of smell to notice body odors and find a mate as our ancestors may have done.