Why two nostrils - Why not one or three?

No question is a stupid question. Why do most animals have two nostrils? If it is just for breathing and smelling, one nostril would do. After all, we just have one mouth!

Two eyes help us see depth and two ears help us determine the direction and distance of the source of sound. So, two nostrils also should help us in some way. They do - they help us smell more things in a better way. 

Before we delve into how having two nostrils helps us smell better, a quick course on how smelling works. Smell is basically a chemical reaction between the olfactory receptors in the nose and the volatile chemicals coming from the object that is being smelled (for example esters from fruits). An object has no smell if it does not emit any chemicals that the receptors in the nose can detect (for example iPhone).

Now that we have established that smell is basically a chemical reaction, one can guess that the rate of this chemical reaction varies based on the molecules coming out of the thing being smelled. Some of them react quickly (like Octane coming from anise) whereas others are slow (like l-carvone coming from peppermint) and thus our nose needs more time with the slowly reacting chemicals before it can detect the smell. This is where having two nostrils helps. 

Different breathing pattern in different nostrils.
In the above diagram, Nostril 1 is the dominant nostril
It has been observed in controlled experiments that all of us have one dominant nostril and one not-so-dominant one (which nostril is dominant keeps changing through out the day without any pattern). The dominant nostril takes in air at the pace required to fuel the body while the other nostril takes in air at a much slower pace. This way, the dominant nostril takes care of supplying the body with enough oxygen and smelling the fast reacting chemicals while the other nostril takes its own time and smells the slow reacting chemicals (it can do so because air passes slowly through this nostril giving enough time for the reaction to occur)

So, there you go. Now you know why nature gave us two nostrils. Human's sense of smell is poor compared to others in the class, but hey, it is at least better than what it would have been if we just had one nostril.

Did the simple science for kids in this post make you a little smarter?
If you have any ideas / questions you want to learn about, please leave a note in the comments section. 
Would be glad to know if there are any inaccuracies in the article.

1 comment:

  1. excellent answer....I love having children around....you learn so much!