Thursday, November 29, 2007

The origins of the olfactory theory of Shape?

If anyone is at all familiar with the theory of perfume breakdown and the notion of searching for how the sense of smell works, then that one is familiar with the conflict between the standard theory of Shape versus Luca Turin's theory of Vibration; the latter explained in Chandler Burr's book "The Emperor of Scent".
To make a long story short, the former theory which is accepted by most people in the fragrance business implies that odoriferous molecules are perceived by our nose through their shape variation, different shapes attaching to one another and producing different effects. Dr.Turin has proposed that it is the vibrational difference of various molecules that accounts for the difference in perception and not their shape. The odour receptors detect the frequency of those vibrations of odour molecules in the infrared range by electron tunnelling.
Of course the modern counterpart to the theory of Shape was the discovery of odorant receptor molecules by Linda B. Buck and Richard Axel. The two scientists were awarded the Nobel Prize in 2004.
The battle carries on still, however, as of yet there is not a complete answer to how olfactory perception is shaped.

But how did the theory of Shape come into being? Perfume Shrine delves in antiquity and elected to present the ancient reference to an allusion to such a notion to our readers. Of course the nature of smell had been debated by Parmenides, Democritus and Xenophanes prior to this, but it is in Lucretius that it takes...shall we say, shape.

Titus Lucretius Carus(96-55BC) proposed that pleasant smells -as well as sensations acting as a pleasant stimulus in general- are composed of smooth particles, while the reverse phenomenon -unpleasant smells and sensations- is due to the hooked nature of the particles that form the material. This was of course intergrated into the research into why the universe is made of pleasant and unpleasant things to man.
Lucretius says:
"Thou traverse through, thou wilt discover thus
That in their frame the seeds of many things
They hide, and divers shapes of seeds contain.
Further, thou markest much, to which are given
Along together colour and flavour and smell,
Among which, chief, are most burnt offerings.
. . . . . .
Thus must they be of divers shapes composed"

"For every shape, which ever charms the senses, has not been brought to being without some smoothness in the first beginnings; but, on the other hand, every shape which is is harsh and offensive has not been formed without some roughness of substance".

{from De rerum natura, book II}

Perhaps this ancient theory of tactility was what gave to rise the concept of smell being perceived through the shape of the atoms of the materials smelled. Or this is my theory in any case...

References: Bailey, C. ed. De Rerum Natura. 3 volumes with commentary. Oxford, 1947.
Buck, Linda and Richard Axel. (1991). A Novel Multigene Family May Encode Odorant Receptors: A Molecular Basis for Odor Recognition. Cell 65:175-183.

Pic of classic 5th century BC chalice depicting a Sphinx courtesy of theoi.com. Chosen for its allusion to a cryptic message, a riddle, and not its chronological frame


  1. Anonymous07:02

    Thank you for this post! Now, here is the next question for you... where is the our sense for beauty coming from. Why do we think a rose smells nice? Is it conditioning? Is it genetically imprinted?
    Fragrant greetings from genetically imprinted andy

  2. You're very welcome Andy :-)
    Glad you liked it.

    I will take you up on your idea and think of something for a future post ;-)

    It's an interesting question to be sure and of course ancient literature is full of such questioning (the joys of having slaves do your mundane tasks; being able to philosophise everything! LOL)

  3. This is why I love Perfume Shrine--erudition with a light heart!

  4. I take this as a *great* compliment dear M! (welcome back, missed you!)


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