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Noses of humans, primates evolved to be less sensitive

Thursday's study joins a growing collection of research that suggests changes in our genetic codes have been chipping away at our sense of smell for years.

(CN) — New research into the genetic journeys of smell receptors further supports the theory that the noses of humans and primates have become less sensitive over time.

While the sense of smell is a near-universal gift for most living animals on Earth, it’s also a subjective experience. Much like its sister-sense taste, what might smell pleasant and comforting to one could offer a nasty assault on the nostrils to another. Some smells can even be missed entirely, as some people can't pick up on specific scents that are obvious to everyone else.

These differences can be traced back to genetics. Scientists have learned over the years that changes and variations in genes can have a direct hand in dictating what kind of smells a person can sniff out — and if those scents will be enjoyable — but questions on how deep this relationship goes continues to pester experts.

To help explore how genetic variations change up our perceptions of smells, on Thursday experts published a study  in the journal PLOS Genetics reveals that people with different variations of odor receptor genes can experience tested scents entirely differently than others — advancing the hypothesis that our sense of smell has lost some of its edge.

The findings, reported by Sijia Wang of the Chinese Academy of Sciences and Joel Mainland of the Monell Chemical Senses Center, were made possible by screening the genomes of 1,000 Han Chinese people as well as another 364 people with ethnically diverse backgrounds.

After testing a series of different scents on their study subjects, their first interesting discovery was the existence of two new smell receptors. The first receptor helps pick up on synthetic musk smells, like the ones commonly used in commercial fragrances, while the other helps detect the potentially less desirable smell compound found in underarm odor.

Researchers found people had different versions of the genes that made these receptors possible, and that people with a certain type had a unique smelling experience. They found that people with an ancestral version of the genes, which is essentially a variant that is shared with non-human primates, reported experiencing a more intense and heightened perception of the tested smell.

Because of this relationship between genetic codes and smell receptors, experts say their findings are more water in the bucket for the idea that humans and other primates see diminishing returns on their nose sensitivity as we evolve.   

“Summarizing all the published genetic variation that associates with odor perception, we found that individuals with ancestral versions of the receptors tend to rate the corresponding odor as more intense, supporting the hypothesis that the primate olfactory gene repertoire has degenerated over time,” the study authors wrote. “This study of olfactory genetic and perceptual variation will improve our understanding of how the olfactory system encodes odor properties.”

While results from Thursday’s study join other efforts to better understand the link between our sniffers and genetic codes, it’s worth noting many of the previous studies used mostly white subjects for their data. Thursday's study relies on data from East Asia but also hundreds of participants from multiple backgrounds, suggesting this peculiar relationship is a constant for all humans.  

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