Question: Why do we have two nostrils?

Kevin Arbuckle answered on 10 Mar 2014:

We have two nostrils so that we can tell the direction a smell is coming from (in the same way we have two ears to let us tell where the sound is coming from).

How this works follows one simple principle – that our nose (and each nostril) can tell how strong a smell is, not just that it is there, and that a smell will be stronger the closer you get to it. Now, if a smell is coming from your right-hand side, it will reach your right nostril slightly before your left nostril, and so it will smell slightly stronger in your right nostril. Your brain then interprets this information to tell you that the smell is coming from the right. In other words, we tell the direction of a smell (or sound) by having two different points to compare its strength (or loudness).

If we only had one nostril, we would have to move towards (or away from) a smell every time we wanted to know which direction it’s coming from, because only then would we get two different points (before and after moving). By having two nostrils, we can get information about where a smell is coming from while staying still.