Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Why do we have two nostrils?

  1. Dec 9, 2009 #1

    Monique

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Something struck me as weird yesterday, every animal that I know of has two nostrils. Why? Why is a single large nostril not sufficient?

    Nasal congestion might be an answer, but in my experience the congestion affects both nostrils at the same time, so you're still not able to breath through the nose.
     
  2. jcsd
  3. Dec 9, 2009 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    I assumed it was to tell the direction of a smell - like two eyes or two ears
     
  4. Dec 9, 2009 #3

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Ha! Sesame Street recently had a segment where they asked if every animal had two nostrils.

    *Dolphins* have one nostril. Whales, too.
     
  5. Dec 9, 2009 #4

    Borek

    User Avatar

    Staff: Mentor

    I can be wrong, but from the videos I have seen I feel like whales - even if they have technically one nostril - seem to have something like nasal septum, so their airduct is still split in half.
     
  6. Dec 9, 2009 #5

    Monique

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    You watch Sesame Street? :uhh:

    A whale has a single blowhole through which they breathe, but do they also have a sensory organ in there that detects scents?

    mgb_phys, if it were for determining the directionality of smell, wouldn't it be very inconvenient to have them right next to each other, only separated by a septum? The eyes and ears are separated for a reason. I don't know of any animal that has nostrils that are located far apart, they are all part of the same nose. Dogs are supposed to have a really good sense of smell, but if they follow a trail they move their head in order to sense directionality.
     
  7. Dec 9, 2009 #6

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Presumably whatever worm type thing we evolved from had a nostril on each side and in the water that mattered. It's less of an advantage in air - and we (and dogs) can always move our heads to find the source.
    It's probably the mechanics of keeping them open that stop them merging completely.
     
  8. Dec 9, 2009 #7

    Moonbear

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Embryologically, our entire head develops as two separate halves, and then fuses in the middle later. So, we have two nostrils for the same reason we have two eyes. This is also the same process that fuses the palate and lips together from both sides (that's why you have that little indentation in your upper lip just below your nose), and why disruption of that process leads to defects like cleft lip or cleft palate.
     
  9. Dec 9, 2009 #8

    Monique

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    But a single nostril would also be symmetrical. A nose with a single opening could be created in the same way that a mouth is, right?. There are embryonic defects that result in the creation of a single nostril or a single eye, so it is biologically not impossible to create one.
     
  10. Dec 9, 2009 #9

    Q_Goest

    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

    No kidding? I've always wondered if my head fused properly....
    Interesting question. Can I ask a stupid one? Are our X chromosomes symetrical? I've always assumed they are not symetrical at all, but never really thought to ask.
     
  11. Dec 9, 2009 #10

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    But you would have more difficulty breathing since there wouldn't be a septum to keep it open,
    It would have to evolve to be smaller or have more cartilage in the nose part - which aren't really evolutionary advantages.
     
  12. Dec 9, 2009 #11

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    Absolutely- I have a 2.5 year old. Seems like you should watch it, too. :)
     
  13. Dec 9, 2009 #12

    Andy Resnick

    User Avatar
    Science Advisor
    Education Advisor
    2016 Award

    according to http://www.enchantedlearning.com/subjects/whales/anatomy/Blowhole.shtml

    "Why do some whales have one blowhole and some have two?
    Most mammals have two nostrils (blowhole equivalents). One of the nostrils (air-passages) of toothed whales evolved into their echolocation system (the sensing system in which they make and receive high-pitched sounds in order to orient themselves, catch prey, and communicate), leaving them with only one blowhole. "
     
  14. Dec 9, 2009 #13
    we have different experiences. :wink:

    my guess (and that's all it is) is that since a primary purpose of breathing through the nose is to warm and humidify the air, a septum increases surface area and makes the process more efficient. evolving a single nostril, unlike a single mouth, would be maladaptive.

    i think mgb_phys' "worm" is actually the http://www.npr.org/templates/story/story.php?storyId=875863" [Broken]. and contrary to that story, they are a lovely thing to have in a home aquarium, where they really aren't pesky at all.
     
    Last edited by a moderator: May 4, 2017
  15. Dec 9, 2009 #14

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Sea squirts are also known as "tenured worms"
    As juveniles they are free swimming with a backbone and simple brain, when they find somewhere permanent to land they become fixed to the rock, their backbone and brain dissolves and they develop a thick skin.
     
    Last edited by a moderator: May 4, 2017
  16. Dec 9, 2009 #15
    lol. i think i originally heard that joke as a sea cucumber, tho.
     
  17. Dec 10, 2009 #16

    Borek

    User Avatar

    Staff: Mentor

    Are you sure it is about worms? I know a lot of people that fit the description.
     
  18. Dec 12, 2009 #17
    Interesting point - I did not know that. Still the question remains why two nostrils - we do not have two mouths and supposedly they (it) developed out of the separate halves you mention.

    If the nose retained the double orifice, and the mouth did not there must be some other explanation for our current situation.
     
    Last edited: Dec 12, 2009
  19. Dec 12, 2009 #18
    While we only have one mouth, just about every thing in our mouths are a mirror image of each side from teeth, taste buds and tonsil's.
    The sense of taste {sweet, sour, salty} is very complex, requiring both nose and mouth. But we really only need one way to fill our stomaches.
     
  20. Dec 12, 2009 #19

    DaveC426913

    User Avatar
    Gold Member

    Bilateral symmetry.

    I expect that the mouth parts developed very early in evolution, before bilateral symmetry, when creautres were very simple in design. But specialized nostrils developed later, after bilateral symmetry was adopted by the more complex organisms.
     
  21. Dec 12, 2009 #20
    hypatia, that occurred to me as I made the comment - that the mouth, without a mouthy septum, is very symmetrical and balanced. But that still does not answer the original question. Howcome we got two nostrils?

    If we are talking about historical priority - then smell has it all over the others, as it is connected to the oldest part of the brain - just about the top of the stem (backbone). We could smell before we could see. Certainly it has had time to get involved in many other things beside just identifying odours - as you say, taste being just one. But could this not be accomplished with a single (maybe whale-like) nose hole?

    oh - hypatia - how is your father Theon? Is he still in that little place in Alexandria? :wink:
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Why do we have two nostrils?
  1. Why do we yawn (Replies: 4)

  2. Why do we Sleep? (Replies: 6)

  3. Why do we have to sleep? (Replies: 15)

Loading...