Nostrils, why two?

[dichotomy]

Nostrils, why two?

 

Why do humans, and many other animals, have two nostrils?

I’d think that one large one would have been more efficient.

[iNow]

Better to have redundancy in a system... a fail safe. One gets clogged, the other still allows for respiration.

[Mr Skeptic]

Bilateral symmetry.

[CDarwin]

Bilateral symmetry.

 

You don't need two nostrils to achieve bilateral symmetry, though. One big one would do. You might be on to something though, in that fetuses suffering from the most severe holoprosencephaly (cyclopia), which is a failure of the protein sonic hedgehog that divides the human head into to distinct, redundant parts at the midline (i.e. creates bilateral symmetry), have a single nostril. So, I suppose it could just be a collateral consequence of how our heads develop.

 

As for articles on the actual evolution of this feature, the best I could do was one from 1924 that I can't find anywhere and one on the evolution of the internal nostril, or choana, from the external nostril.

http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=745272

http://www.ncbi.nlm.nih.gov/pubmed/15525987?ordinalpos=5&itool=EntrezSystem2.PEntrez.Pubmed.Pubmed_ResultsPanel.Pubmed_RVDocSum

 

Here's one interesting functional role:

http://www.nature.com.proxy.lib.utk.edu:90/nature/journal/v402/n6757/abs/402035a0.html

Apparently your two nostrils are optimized to slightly different smells.

[John Cuthber]

There's another reason. You generally use one at a time for most of your breathing.They swap responsibility for handling most of the air from time to time.

This means the air is drawn through them at different rates and this, in turn, means that you can detect a greater range of odours. (The distinction between which odour moleculr=es are more likely to be spotted by which nostril is comparable with the difference between kinetic and thermodynamic control of chemical reaction paths).

[dichotomy]

Apparently your two nostrils are optimized to slightly different smells.

 

Amazing. It makes so much sense now. I would have thought it was just a relic.

Why we have two eyes and ears is more obvious of course, but can the same be said, that is, does each eye pick up vision in a slightly different way? and each ear may pick up vibrations in a slightly different way?

[iNow]

does each eye pick up vision in a slightly different way? and each ear may pick up vibrations in a slightly different way?

Yes.

Hence stereoscopic vision and echolocation.

[Vexer]

(Well, that was interesting).

[dichotomy]

Ok, what about the forked tongue of a snake. Does each tip on the fork serve that slightly different, handy, sense service?

[DrP]

IIRC from watching David Attenborough, the fork in the tongue allows the snake to sense direction as well as smell/tase. It picks up scent through tasting the air - the fork gives it 2 refference points with one being more potent than the other so it can tell which direction it's prey went.

[gcol]

Bilateral directional olefactory senses..... Now I know how I can immediately tell which luncheon companion has farted. Very handy, problem solved. Then again, if having two nostrils is so useful, perhaps the question should be why only two?

[iNow]

It might have something to do with the fact that the guy with three nostrils couldn't get laid.

[gcol]

I knew a girl with three nostrils who could play three-part harmony on the Mongolian nose-flute. A rare talent.

[DrP]

I knew a girl with three nostrils who could play three-part harmony on the Mongolian nose-flute. A rare talent.

 

 

yea right!

 

 

 

I knew a guy with 3 nipples at school - he never got laid either.

[Phi for All]

It might have something to do with the fact that the guy with three nostrils couldn't get laid.

Women are just going to have to give up their quaint notions of what's attractive if this species is ever going to evolve something really spectacular. Are we to miss out on something as cool as a shark's tooth replacement just because women won't date a guy who leaves his teeth lying around like toenail clippings?

[thedarkshade]

You know, evolution has its strange and blind ways of working, but it keeps ending up with the best solutions.

[Phi for All]

You know, evolution has its strange and blind ways of working, but it keeps ending up with the best solutions.

Tell that to my retinas.

[thedarkshade]

Tell that to my retinas.

You surely had a hand on that, I assume.

[Phi for All]

You surely had a hand on that, I assume.

No, it was busy with my nostril.

 

 

And don't call me surely.

 

 

 

 

 

[dichotomy]

 

 

What about eye brows? Why two?

[iNow]

What about eye brows? Why two?

 

That's almost certainly a product of mate selection, but functionally, a larger brow ridge, one enhanced with hair, helps the person to have better vision in bright conditions. Sort of like wearing a hat with a brim to keep the sun out of your eyes. Before hats, eyebrows would have served similar purpose.

 

Again, though, for some reason brows were found more attractive during mate selection. I just can't understand why, myself.

 

 

 

 

 

 

 

 

 

 

 

 

 

[CDarwin]

Ok, what about the forked tongue of a snake. Does each tip on the fork serve that slightly different, handy, sense service?

 

If I'm not mistaken, the tongue doesn't actually do much 'sensing.' It only communicates the air back to the Jacobson's organ which does the actual chemoreception. I could be wrong.

[dichotomy]

Well, at least that guy has a larger than normal cranial casing.

[Vexer]

I think people have two nostrils for the same reason that men have nipples.

[dichotomy]

I think people have two nostrils for the same reason that men have nipples.

 

 

What, to produce milk?

 

Is it urban legend that some concentration camp male prisoners in WWII developed breasts or enlarged mammary glands to feed the babies that had no mothers? I doubt this is true, but I don't know really.