What the Nose Knows - Avery Gilbert [1]
—ALEXANDER GRAHAM BELL, 1914
No satisfactory classification of odours can be given.
—Encyclopaedia Britannica, 1911
HOW MANY SMELLS ARE THERE? IT’S AN ODD QUESTION, but give it some thought. Mentally flip through the pages of your personal smell catalog. You find burnt toast, shaving cream, Grandma’s kitchen, and pine trees. There’s the weird glue in the binding of that pocket-size Latin/English dictionary from high school. With a little effort you can come up with a lot of smells, but putting a number to them is difficult. How does one count the odors of a lifetime, much less all the odors in the world?
Some people aren’t daunted by the task: they simply estimate. Better yet, they pass along estimates made by others. Journalists like to say that we can smell thirty thousand different odors. The New Age guru Michael Murphy cites this figure in The Future of the Body (1992): “According to the calculations of one [fragrance] manufacturer, an expert can distinguish more than 30,000 nuances of scent.” Murphy, in turn, got the number from Vitus Dröscher, a German pop science writer (1969): “A perfume manufacturer has worked out that a real expert must distinguish at least thirty thousand nuances of scent.” Dröscher doesn’t provide a source. Perhaps it was in Science Digest (1966): “Industrial chemists have identified some 30,000 different smells.” Unfortunately, the magazine didn’t provide a source either. What this proves, I suppose, is that dubious facts thrived in the media long before the Internet.
One would like to think that smell scientists have a better grasp of the matter, and indeed they prefer to quote a different estimate. When Linda Buck and Richard Axel won the 2004 Nobel Prize for discovering the olfactory receptors, the Nobel Foundation issued a press release. It noted that people recognize and remember “about 10,000 different odours,” a figure the Swedish publicists took from the prize winners themselves. Surely that’s a number we can take to the bank. But the number 10,000 didn’t originate with Buck and Axel: it had been tossed about for years by other scientists. Something about it had always bothered me—why such a nice fat round number? Why was there no date of discovery? And, strangest of all, why did nobody take credit for it?
If you try to track down the mysterious number 10,000 to its original source in the scientific literature, you are in for an adventure; like walking a maze, dead ends abound. For example, I began with a paper in Behavioral Ecology (2001), which I followed to another in Trends in Genetics (1999), which in turn didn’t provide a source. I started again, this time with a prominent smell researcher, the Brown University psychologist Trygg Engen. In 1982 he wrote, “Some have claimed that an untrained person can identify by label at least 2,000 odors and an expert can identify as many as 10,000.” Engen credits this claim to R. H. Wright, Canada’s most famous smell scientist. Wright seemed a likely source, at least until I read what he actually wrote, back in 1964: “[I]t seems likely that the average person would have no trouble in distinguishing between several thousand odours, and an experienced authority in the field has claimed the ability to recognize well over ten thousand. Still another has simply said the number is apparently unlimited.” Wright goes on to say, “It would be an interesting exercise to design an experiment to verify these estimates.” Ooof! So Wright didn’t discover any number at all—he just passed along what he had heard and Professor Engen repeated it. These eminent smell experts remind me of kids at summer camp passing along ghost stories.
I was beginning to think I’d never find the source of the magic number 10,000, when I found it once more in a 1999 food chemistry textbook. From there I followed it to a 1966 paper, and then to a paper published in 1954 by researchers from the Arthur D. Little, Inc., consulting company. At a scientific conference the previous year, the