The Nose Knows

The human nose can differentiate more than a trillion odors, a study finds.

By | March 25, 2014

FLICKR, DENNIS WONGThe human nose can smell an average of a trillion different odors, according to a study published last week (March 21) in Science. For decades, researchers believed that the human nose could only perceive around 10,000 different smells, but that number was based on an estimate from the 1920s that hadn’t been empirically tested.

A team led by Andreas Keller from Rockefeller University in New York City used 128 distinct molecules to mix smells that contained 10, 20, or 30 compounds each, and asked 26 volunteers to distinguish the smells. If the scents had more than 51 percent overlap, most study participants couldn’t tell them apart, but if they had less than 57 percent overlap, most subjects could easily distinguish them. The most sensitive smeller could distinguish 10 million trillion trillion scent combinations; the least sensitive could detect a mere 70 million different smells. That made for an average of 1.7 trillion.

“There are probably billions of odorous molecules and we only worked with 128 of them,” Keller told National Geographic’s Not Exactly Rocket Science. “Furthermore, we only mixed 30 compounds. There are many more mixtures with 40 or 50 components.”

“The research goes a long way to addressing the capability of the human olfactory system, but there are still specific questions to be answered about exactly how many individual chemicals can be perceived,” Stephen Liberles of Harvard Medical School, who was not involved in the research, told Nature News.

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Avatar of: dmi


Posts: 2

March 25, 2014

"If the scents had more than 51 percent overlap, most study participants couldn’t tell them apart, but if they had less than 57 percent overlap, most subjects could easily distinguish them" - am I missing something here, or is one of the percentages a typographic error? If there were 54% overlap, most subjects BOTH couldn't tell them apart AND could easily distinguish them.

Avatar of: James V. Kohl

James V. Kohl

Posts: 476

March 25, 2014

I would have erred had I not cited other works by Vosshall and Keller in the concluding sentence of my 2012 review: “Human pheromones and food odors: epigenetic influences on the socioaffective nature of evolved behaviors.”

“Socioaffective neuroscience and psychology may progress more quickly by keeping these apparent facts in mind: Olfaction and odor receptors provide a clear evolutionary trail that can be followed from unicellular organisms to insects to humans (Keller et al., 2007; Kohl, 2007; Villarreal, 2009; Vosshall, Wong, & Axel, 2000).”

Now that our detection abilities have been evaluated, I wonder why there is no mention of our ability to detect species-specific social odors, called pheromones. It’s become obvious that conserved molecular mechanisms link the epigenetic landscape to the physical landscape of DNA in species from microbes to man. Other recent reports attest to that fact:

1) “Detecting Fat Content of Food from a Distance: Olfactory-Based Fat Discrimination in Humans

2) “The Scent of Disease: Human Body Odor Contains an Early Chemosensory Cue of Sickness

Therefore, in the context of our detection abilities, I think others may have erred by not citing one of my other reviews: “Nutrient-dependent/pheromone-controlled adaptive evolution: a model

Clear attestations to the plasticity of our olfactory system, which links ecological variation to ecological adaptations, now suggest that “adaptive evolution” should be called ecological adaptation. In the presence of food odors and nutrients that metabolize to species-specific pheromones that control the physiology of reproduction, ecological adaptation is what’s expected to occur.

What this latest report now shows is the degree of fine-tuning that is possible after ecological, social, neurogenic, and socio-cognitive niche construction has already occurred — and resulted in the nutrient-dependent pheromone-controlled increased organismal complexity that is us.

Now that Mainland et al have published “The missense of smell: functional variability in the human odorant receptor repertoire” and Foote et al have published “Tracking niche variation over millennial timescales in sympatric killer whale lineages,” the similarities at the top of the aquatic and terrestrial food chains attest to the power of conserved molecular mechanisms to link cause and effect across all species via olfaction and odor receptors, which is what I detailed in the review I submitted last week.

Avatar of: JP_STATE


Posts: 1

Replied to a comment from dmi made on March 25, 2014

March 27, 2014

Yes, this did not make sense.

so I went to the original science paper and I believe this newz report is intepreting the paper results incorrectly.

this is what I make of the paper:

"most subjects can discriminate mixture pairs that overlap by less than 51.17%"... that is where the 51 comes from.

Then in the next sentence:

"Most (scent) pairs that overlap by less than 57.43% can be discriminated" this is where 57% comes from.

so, one % refers to predicting the number of people that will be able to tell appart two fragrances given the overlap and the other one is the proportion of frangrances with a certain overlap that can be reliably discriminated.

To understand the subtleties behind these differences you need to read the paper (link in the column), I guess.

I still thank the columnist who put this interesting piece under our radar.


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