The pas de deux of questions and answers

Can’t Have One without the Other: Questions and Answers

The first of the science and engineering practices is “asking questions” followed by numbers two through eight focused on how to construct answers. As we progress through school, we are taught the answers (the three causes of the Civil War, the capital of Delaware, and Avagadro’s number) but not necessarily the questions from which they sprang. The following presents an example that shows why it makes sense to keep questions and answers together.

First a little test.

 How many different smells or odors can humans identify?

a) 25.

b)  10,000.

c) 250,000

d) more than 1 trillion.


If you look in the textbook called Molecular Cell Biology, by Alberts and others, 4th edition, 2002, where you would have found:

“Humans can distinguish more than 10,000 different smells (odorants), which are detected by specialized olfactory receptor neurons lighting the nose… It is thought that there are hundreds of different olfactory receptors, each encoded by a different gene and each recognizing different odorants.”


It looks like the number 10,000 is a good bet to be the correct answer.

However, Avery Gilbert, a sensory psychologist and author of What the Nose Knows, was always suspicious of this “fact.”

Something about it has 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?

Dr. Gilbert found out the origin for the “answer” of 10,000.

Back in 1927, two American chemists —Ernest C. Crocker and Lloyd F. Henderson —searched for the answer to the question “is it possible to create a numerical coding system in which any smell could be assigned a four-digit identifier?”

In developing their classification system the chemists found out that using their coding system it was mathematically possible to identify 6,561 different smells. The number was later rounded up to 10,000.

The chemists never conducted an actual experiment to test the smell-ability of actual humans. So while 10,000 is indeed an answer, it is most certainly not the answer.

What the original quest? How many odors can a human being detect?

The March 24, 2014, edition of The Washington Post reported the results of an experiment done to answer that question. The research was done at the Rockefeller University in New York.

The experiment’s chief investigator, molecular neurobiologist Leslie Vosshall, developed an experiment modeled on how hearing exams are conducted. In a hearing test listeners must try to distinguish between different tones. In the Rockefeller experiment 26 different noses were put to the test. “Each individual was given three vials, two of them containing the same sand and has to determine which smell was the odd one out.”

As a result of data gathered in the hundreds of repetitions, the researchers assumed that subjects’ performances on the test would be similar if asked to recognize more of the possible smells that could be produced in the lab. From these data it would appear that the average human should be able to distinguish at least 1 trillion different odors. The study was published online in the journal Science. (, March 21, 2014)

The point is that questions and answers are related in a pas de deux, a dance in which two dance partners follow one another’s steps.

It seems that if you want to understand the answer, you also must  know the question.



Avery Gilbert’s blog First Nerve


Washington Post, March 20, 2014.–far-more-than-thought-says-study-of-smell/2014/03/20/ffb8644a-af95-11e3-95e8-39bef8e9a48b_story.html


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