I was talking with some friends today about how the nose senses smell and how one can tell where the smell is coming from when I realized a cute little hypothesis which might actually have some truth in it. It appears to me that if smell were to travel through air in the way sound or light travel, people would have been a lot uglier than they are now! And if you bear with me for just a little longer I'll try to present the arguments which support the case that I have not gone mad.
Both sound and light travel as waves through the air. I may now resort to writing the equation of a traveling wave but that would do nothing but cloud the issue. What is important is that if a disturbance travels as a wave through a medium, like sound and light do, then it is possible to make a measurement of that wave at more than 1 location and say something about the location of the source of the wave. That is why we have two eyes and two ears because if we had only one of each then we would not have been able to determine the location of sources of sounds or the depths of objects. The accuracy with which the location of the source can be determined depends upon the distance between the points at which the measurements are made. In general, the closer they are to each other, the more inaccurate the assessment of the location. Now it is not hard to see how the accurate and efficient evaluation of sounds and objects would have been a winning and desirable strategy in the game of evolution. Therefore nature, being the brilliant designer that she is, has separated our two eyes and two ears by a considerable distance. To my limited biological knowledge, it appears true with all other species but I would be interested to know if this assessment is not correct. In fact, I would go as far as saying that if a sufficiently evolved alien specie were to be discovered on another planet and if it had auditory and visual sensors, they would most probably be in pairs (if not more) and that they would be separated on the 'face'.
This brings me to the point of this post. Smell doesn't travel through air like a wave and, therefore, its source cannot be as easily located in space as the sources of sound or light. The only way in which the source location problem can be tackled for smell, it appears to me, is by using its intensity and this is an inherently more inefficient way than by using the phase information for sound or light waves. Intensity processing also doesn't require measurements separated in space. It appears, therefore, that nature could do only so much for smell localization. It bestowed upon its creatures more sensitive noses but their nostrils were packed together because there is no inherent advantage in having them spread apart. And now the final picture emerges. If only smell traveled through space like sound and light do, our nostrils would most probably have been spread apart and what a ghastly scene that would have constituted! With twice the number of independent facial fissures humanity would surely have been a trainwreck, and for all we know it may just be possible that that quintessential fuel of the evolutionary machinery, mating, may have been resolutely refused by all. It would really have been a nightmare!