Human sense of smell might even gradually fade, according to a study that found that humans have different versions of 2 scent receptors for musk & body odor.
Olfactory receptors notice airborne-chemicals that waft into our noses, however smell receptors vary vastly from 1 person to the next.
According to a 2013 study, two people, on average, will have functional differences in more than 30% of their odor receptor genes. Which is why some people may find some smells-pungent or pleasant that next person can’t even detect.
In this new study, Bingjie Li of Shanghai Institute of Nutrition and Health & colleagues asked 1,000 Han Chinese & 364 ethnically diverse people from NY to-take a whiff of 10 scents, including 2 odors that people often perceive differently or not at all : a synthetic musk called Galaxolide & a key molecule linked to human underarm odor.
What they found supports a long-standing hypothesis that the human sense of smell may have diminished over time due to changes in genes that [encode] our smell receptors. However, not everyone agrees with that hypothesis.
Participants rated the intensity & pleasantness of odors on a 100-point scale, and researchers looked at genetic-variation in their olfactory genes, hoping to find changes related to how people perceive-scents.
“The comparison of this perceptual variability with genetic variability enables us to identify the role of single-odorant recipients” Li & his colleagues writes.
The team identified 2 new odor receivers: one that senses galaxolide, a “clean,” sweet, & powdery scent used in many fragrances, and another that recognizes the chemical called 3M2H, one of the approx. 120 compounds that make up human body odor.
The mutations of the genes that encoding these receptors influenced if people perceive the scents as strongest or less intense, but genetics explains only a small part of the difference.
Li and his colleagues have examined these 2 new-found genetic changes and 27 other known odor related mutations, comparing the evolutionary age of each mutation slipped in-to our genomes and it is believed that the changes would make human smell recipients less or more sensitive to odors.
“Summarizing the entire published genetic variation that associates the perception of the smell, we have discovered that people with ancestral versions of receptors tend to-rate the corresponding odor as more intense” authors writes, adding that this evidence suggests that humans’ sense of smell has faded over time.
“Although this study has not been designed to directly treat this hypothesis and may suffer from selection bias, these data support hypothesis that the primate olfactory gene repertoire has degenerated over-time,” they write.
This idea isn’t new: There’s a long-running theory, though some call it a myth that humans lost their sense of smell when sight became our dominant sense.
This theory is fueled by the fact that humans & other primates have hundreds fewer olfactory genes than mammals that follow their nose like rats & mice, and about half of smell genes we don’t have no-longer function.
However, the suggestion that [humans sense] of smell slowly fades over-time has been hotly contested, so let’s take a look.
Other researchers have created the case before that our sense of smell isn’t as dangerous as we would think, inform to smell-test studies that recommend that even with fewer olfactory genes than other animals, humans knack of discerning smells out-performs our own expectations and even other animals – depending on the scent.
“Humans, like other mammals, can distinguish an incredible number-of scents and even follow outdoor scent trails,” wrote neuroscientist John McGann of Rutgers University in 2017.
What counts, McGann told Ed Yong at The Atlantic in 2017, isn’t the number of genes encoding smell receptors, or perhaps how many neurons humans have in their olfactory bulb, that sits on top of the nasal cavity & processes data regarding odors, but how they work to perceive the sense of smell. Ours seems to be working fine.
Our understanding is also clouded is the bias of studies to-date, some-thing which the latest study attempted to address.
“The typical [olfactory] study focuses on Western participants who live in a culture where smell is not particularly sophisticated,” psychologist Asifa Majid of Radboud University told Yong in 2017.
“But people in other parts of the world are better at recognizing smells, differentiating & calling names,” Majid said, like the Jahai people in Malaysia.
Maybe most of us are just out of practice’.
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