Friday, November 7, 2014

​Can We Really Smell One Trillion Different Scents?


A paper published in Science magazine this past year made international headlines when it answered a simple question—how many odors can we smell?—with a massive figure, finding that our noses can distinguish as many as one trillion individual odors. The report was widely lauded by the media:  A testament, amidst all the depressing stuff hitting our newsfeeds on the daily, to our evolutionarily endowed awesomeness.

Or, just maybe, it's a testament to our predilection for buying into splashy, paradigm-shattering claims about just how great we are?

In a pre-print released several days ago on Cornell University’s open archive arXiv, Caltech neuroscientist Markus Meister claims the trillion odors figure is off by “astronomical factors.” By re-running the authors’ own experiments, Meister comes up with far more pedestrian estimate for the number of smells the average person can discriminate: Ten.

Now, as you probably guessed, you can smell more than 10 scents, and that's the point. According to Meister, the paper’s optimistic claims about the human nose are based on flawed mathematical logic. Using that logic, Meister showed that either 10 or a trillion scents could be calculated as the correct answer for the human scent limit.
We don’t actually know the number of dimensions that exist for olfaction
It’s a smelly, complicated world out there. Most of the scents we encounter in nature are actually amalgamations of dozens to hundreds of different odiferous compounds— the “scent” of a rose is composed of over 275 unique molecules. And while we have clearly defined boundaries for human vision (390-750 nanometer wavelengths on the electromagnetic spectrum) and hearing (20-20,000 hertz), it’s proven much harder to gauge the limits of our sense of smell.

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