Why do we have two nostrils instead of one?

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Having two ears or two eyes is intuitively effective because it allows us to sensibly capture what is going on around us much better but we come to question why is it necessary to have two nostrils instead of one?


Thanks to our two eyes, we can better calibrate how far away objects are: the brain combines the two visual stimuli from both eyes to produce a more three-dimensional picture of the world. We can detect where a sound is coming from if it sounds louder in our right or left ear. 


But does having two nostrils allow us to capture smells more vividly? Some researchers believe so, but the advantage of having two nostrils goes far beyond that.

It's all about moisture and mucus

Dogs have two nostrils because they can record separate air samples with each nostril, allowing them to compare them to establish the source of a particular odour. 

This spatial olfactory perception also seems to have been studied in snakes, as Kelly Weinersmith and Zach Weinersmith explain in their book An Elevator to Space: "The snake extends its forked tongue to capture chemicals in the saliva. It then rubs its tongue against two slits in the roof of its mouth and the saliva enters two small lumps known as vomeronasal organs, where the chemicals captured by the saliva are analyzed.


In humans, however, what makes it possible to have two pits instead of one is the possibility of alternating which one to breathe through at any given time, which makes it easier for neither to dry out too much. In other words, if we had only one pit and it dried up or became clogged, we would have no choice but to breathe heavily. On the other hand, if we have two and one dries out, we will still have the other to breathe properly, in the event that it continues to be wet.

This is particularly important if we want to prevent the nasal tissue from being damaged or not functioning properly.

In order to make the nose free of obstacles to breathe and smell, while partially sterilizing the lower respiratory system, we have the mucus and cilia, a kind of microscopic brushes that push the mucus towards the mouth at an average speed of 6 millimeters per minute, either to spit it out or to swallow it. Some of this mucus, two or three litres every twenty-four hours, is eventually swallowed and serves to replenish the gastrointestinal mucosa. 


This mucus also serves to trap dust particles and other elements that could get into our body, including bacteria. The movement of the cilia is important to drag everything into the stomach, so if they work slowly (for example, because it is very cold), the likelihood of us catching a cold increases. 

So, in order for the system to always work optimally, according to research by the U.S. National Library of Medicine, our nostrils are alternately plugged and uncapped. "At all times, one nostril is more likely to absorb air than the other, thanks to the nasal venous sinuses, which swell alternately in a process called the nasal cycle.

Some experts point out that another reason this occurs daily is that it also optimizes our sense of smell, because some odours are better recorded if they enter the nostrils quickly, and others are better appreciated if there is slight congestion involved.

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