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Binocular vision gives us a 3D perspective, and two ears let us locate the direction of a sound. But why two nostrils?
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David Muir
Edinburgh, UK
First, press your finger against the left side of your nose to close the left nostril. Breathe deeply through your right nostril. Now, close your right nostril and breathe through your left nostril. You will probably notice that you breathe more freely through one nostril than the other. If you try this at other times in the day, you may find that the freely breathing nostril has swapped sides – and then later, it swaps back. This alternation is called the nasal cycle.
Your nose has two jobs. It is our centre for our sense of smell and the entrance for much of our air intake. The easier-to-breathe-through nostril is good at taking in air but is less efficient at detecting smell. The low-flow nostril is better at detecting scent molecules, as they have more time to dissolve in the fluid covering the scent receptors.
So, why the alternation, rather than each nostril specialising in fast or slow airflow? It seems to be an evolutionary answer to optimise both olfaction and air conditioning by maintaining a good sense of smell while preventing one nostril from drying out.
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