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‘Wake up and smell a trillion things!’ Noses detect billions more smells than previously thought

Published time: March 21, 2014 13:19
AFP Photo/ Raul Arboleda

AFP Photo/ Raul Arboleda

Our noses apparently can distinguish billions more smells than previously believed – about a trillion – according to a new study. But our own evolution has prevented us from 'smelling' it all clearly.

"Our analysis shows that the human capacity for discriminating smells is much larger than anyone anticipated,” co-author of the American study, Leslie Vosshal told AFP. Vosshal is the head of Rockefeller University’s Laboratory of Neurogenetics and Behavior.

The results were published in the journal Science.

Although hard to believe, the last time science bothered to test the human sense of smell was way back in the 1920’s – and it didn’t back up its results with empirical data; it discovered that we have 400 olfactory receptors up there, and that was that.

By comparison, this made the human eye and its three receptors appear like space-age technology, with its capability to distinguish several million different shades and colors. The ear, meanwhile, is capable of telling 340,000 sounds apart.

That’s why Vosshal is excited that the new research – which involved 26 participants smelling 30 different combinations made up of 128 odorant molecules – bore fruit.

Reuters / Adrees Latif

"We didn't want them to be explicitly recognizable, so most of our mixtures were pretty nasty and weird,” she said of the methods used, adding that the team “wanted people to pay attention to ‘here’s this really complex thing. Can I pick another complex thing as being different?”

Therein lay the inherent difficulty with smell. It’s much less clear-cut than other senses. By testing combinations with varying degrees of similarity, the team was able to grasp the magnitude of it all. For each group of participants, the scientists created combined odors with the same quantity of molecular components, but slightly varying composition.

Each participant was offered three vials, two of which contained the exact same odor, while the third contained a different smell, but with very miniscule differences from the first two. The third aroma also consisted of the same number of molecular components as the first. The participant then had to pick the odd one out.

What they found further complicated things: the degree of variability of results and individual sensing abilities led to the conclusion that other, differing types of tests need to be performed.

Andreas Keller, head researcher on the Rockefeller team, believes that “a huge part of the variability is due to genetic variability in the odorant receptors that bind to the odors.”

The real point of this was to show that there are virtually endless combinations of molecules producing infinite variations – and furthermore, different reactions. But cultural adaptation and standardization of odors – be it out of personal hygiene or refrigeration – have somewhat dulled noses, researchers say. And who really wants to know the 15 different aromas of an apple? It would simply make modern life more complex, so nature and society simplified it for people.

Keller believes the above explains why people have learned not to rely on the sense of smell nearly as much as they do on sight and hearing. Digging even deeper, Keller sees physical evolution into an upright species as also of great significance to abandoning noses as accurate instruments – we simply stand too far away from the ground below our feet.

What the Rockefeller University team found in the course of the study, they believe, goes a long way toward explaining the evolution of human behavior and brain functioning as well, and further studies are most certainly needed to explore that in detail.

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