PDA

View Full Version : Why Do We Have Two Nostrils?


fishbait
3rd November 2007, 04:07 PM
Other than being a boon to the nosering industry, what is the advantage of two nostrils rather than one big one? Are there any mammals with one nostril?

If all or most mammals are so equipped, there must be some advantage in having two. Do we possibly smell in "stereo" as an aid in determining directional source of odors?

MrQhuest
3rd November 2007, 04:55 PM
I remember an article some time ago, where it was determined that we do smell in stereo. The only mammals I am aware of with one nostril are whales and dolphins. Which brings up a related question. Do whales and dolphins have a sense of smell like other mammals?

Mr Qhuest

Dr Adequate
3rd November 2007, 05:00 PM
Yes, it'll be smelling in stereo. There are fish, by the way, with paired nostrils which (having no choana) they do not use for breathing.

Plantfoam
3rd November 2007, 05:03 PM
Also, perhaps there is an added benefit of having a small nostril that warms incoming air....and two of these allow sufficient airflow to take place.

I'm done being sciency now.

Rasmus
3rd November 2007, 05:07 PM
I recall reading somewhere that the nostrills swell and decongest in turns. So the main breathing happens on only one side at a time, giving the other nostril a chance to - and here I forget what it was and am more guessing than anything - rebuild moisture or clean itself from the impurities taken from the air.

It certainly feels like that to me when I have a cold (far too often) and find breathing through my nose difficult. That seems to me to be a one-sided problem.

Skeptic Ginger
3rd November 2007, 05:14 PM
I'm not sure you should assume 3D smelling would occur by the same mechanism as 3D vision or 3D hearing. It's not hard to find where a smell is coming from by following the stronger concentration. If 3D were involved in smelling I think you should see some mammals with nostrils closer together and some further apart. You see that with vision.

Also, light and sound waves have certain properties which interact with your two eyes and two ears in a completely different manner than the chemical triggers of odor which are distributed as a gas, not as a particle/wave.

A more logical explanation for two nostrils is it is a random result of the bilateral nature of our bodies. Having two arms, two legs, two eyes, etc was likely the selected attribute and two nostrils came along for the ride.

The other advantage could be more turbinate surface which filters inhaled air.

Skeptic Ginger
3rd November 2007, 05:16 PM
I don't think what you heard was correct, Ras. Infection and allergy don't alternate nostrils. There is no physiologic mechanism for it to occur that I am aware of.

wahrheit
3rd November 2007, 05:19 PM
It certainly feels like that to me when I have a cold (far too often) and find breathing through my nose difficult. That seems to me to be a one-sided problem.


That was exactly my first thought reading the OP. Unlike you, I rarely do have a cold (lucky bastard), but whenever this happens I notice that one side of my nose is stuck, while the other one works pretty well for breathing.

However, I'm sure the real reason for two nostrils is better explained by the above mentioned 3D smell or bilateral thing.

Well, maybe it's a mix of both. Or maybe a helpful secondary effect. I sure hope so. ;)

Skeptic Ginger
3rd November 2007, 05:19 PM
Also, perhaps there is an added benefit of having a small nostril that warms incoming air....and two of these allow sufficient airflow to take place.

I'm done being sciency now.Two turbinates, more surface area. Both warming of incoming air as well as filtering of particulates occur in the turbinates.

Mojo
3rd November 2007, 05:21 PM
Why not three or more nostrils?

Skeptic Ginger
3rd November 2007, 05:22 PM
Yes, it'll be smelling in stereo. There are fish, by the way, with paired nostrils which (having no choana) they do not use for breathing.But they are still bilateral organisms. So 3D is not the only explanation.

I don't think you all are considering the difference in the properties of particle/waves and gases.

wahrheit
3rd November 2007, 05:28 PM
But they are still bilateral organisms. So 3D is not the only explanation.

In other words: Why do we not only have two nostrils, but also have two arms, two legs, two (four) cheeks, two of a lot of things?

Rasmus
3rd November 2007, 05:31 PM
I don't think what you heard was correct, Ras. Infection and allergy don't alternate nostrils. There is no physiologic mechanism for it to occur that I am aware of.

I may have been unclear:

It's (according to what I remember) always the case that one nostril does most of the work, whilst the other is partially blocked and thus in recovery-mode.

But when I suffer from a cold I notice that my two nostrils tend to be differently efficient. It means I cannot inhale enough air and my sensation of the inactive nostril seems to respond to the air preasure due to the breathing that it cannot compensate simply by letting air pass through it.

TX50
3rd November 2007, 05:38 PM
...The only mammals I am aware of with one nostril are whales and dolphins. Which brings up a related question. Do whales and dolphins have a sense of smell like other mammals?

Mr Qhuest

Mysticetes (Humpbacks, Blues, Gray's, Bowheads, Rights etc) all have
two "nostrils". Odontocetes (Sperm whales, Dolphins, Bottlenose whales etc)
have one (the other having evolved into part of their echolocation system).

I would think that the reason you have two is purely to do with the way
bilaterally symmetrical bodies are constructed. One of everything down the
middle, two of everything down the outside.

Skeptic Ginger
3rd November 2007, 05:49 PM
Why not three or more nostrils?Why not 3 arms? Mammals evolved with a particular formula which is retained despite the wide variations in the basic model.

If you divide mammals in half, you have symmetry. Star fish differ. Octopi partially differ. Plants differ. Some of our internal organs differ from the bilateral format. But almost everything else is mirrored halves.

That can be because it has an advantage. Still, things which allow the organism to exploit a particular niche give us incredible variation. Yet we have little variation in our symmetry.

If you look at how the instructions from the DNA result in the fetus developing and allow for mutations not to devastate the organism thus allowing evolution to occur, I think you might find that the mechanism of fetal development includes a kind of segmentation which perhaps just meant the symmetry of the original mammal is retained despite other changes. After all, the mechanism of fetal development in mammals is also consistent across species.

A little more explanation may help. The genetic information which encodes fetal development is segmented. A single or relatively few mutations give you a 6th finger. With that single event you get 6 fingers on both hands. And maybe you even get 6 fingers on each hand and 6 toes on each foot. You get complete fingers with skin, bone, muscle, cartilage, blood vessels, nerves, the same hair distribution as on your other digits, the same sweat gland activity and so on. The reason for this is the mutation changing the number of digits didn't involve the other structures of the digits.

If a mutation to give you a whole finger had to be as complex as all the genetic information which is used to grow a finger, evolution just couldn't function. You would need too many specific random mutations to get any changes which actually changed the organism.

So evolution is random and not random at the same time. Mammals retain the same original model underneath a lot of variation. Two nostrils, not 3 or 5. The nasal septum could disappear just as there is only one digestive track and one trachea, but there doesn't necessarily have to be a specific advantage of two nostrils in order to retain the feature.

If there was an advantage, then I'd still bet on surface area. Surface area has a particular use in both the respiratory and the gastrointestinal tract. But with food, feeding one mouth clearly made more sense than feeding two.

And now that I think about it, since the nostrils are involved in breathing and smell, there is no reason to think 3D smelling controlled the evolution of the nose. For better sense of smell better neurology is involved, not greater distance between nostrils. While for breathing, turbinate surface area matters. Those are a pretty good indicators 3D smelling is not what resulted in two nostrils while turbinate surface area could have.

Rasmus
3rd November 2007, 06:10 PM
One of everything down the
middle, two of everything down the outside.

Wow, you must look ugly. Where is your nose located, exactly? ;)

MrQhuest
3rd November 2007, 06:27 PM
TX50,
I stand corrected. Thank you.
Time to head over to Wikipedia for a while.

Mr Qhuest

Walrus32
3rd November 2007, 06:42 PM
It's obvious...we have two nostrils so we can breath and pick our nose at the same time. And it works equally well for the right- or left-handed.

fishbait
3rd November 2007, 07:13 PM
From here: (http://www.abc.net.au/science/k2/moments/s198395.htm)

And it now turns out, that each of our two nostrils can pick up different smells.

Another interesting fact:we all have three sets of erectile tissue in each nostril - the same sort of erectile tissue found in the penis and clitoris. "Is your nose normally that size or are you just glad to see me?":D

Jeff Corey
3rd November 2007, 07:26 PM
And does the Man With Three buttocks have two anuses?

firecoins
3rd November 2007, 07:34 PM
we looked funny with one nostril. So we decided we needed 2 instead.

neutrino_cannon
3rd November 2007, 07:40 PM
I'm not sure you should assume 3D smelling would occur by the same mechanism as 3D vision or 3D hearing. It's not hard to find where a smell is coming from by following the stronger concentration. If 3D were involved in smelling I think you should see some mammals with nostrils closer together and some further apart. You see that with vision.

Also, light and sound waves have certain properties which interact with your two eyes and two ears in a completely different manner than the chemical triggers of odor which are distributed as a gas, not as a particle/wave.

A more logical explanation for two nostrils is it is a random result of the bilateral nature of our bodies. Having two arms, two legs, two eyes, etc was likely the selected attribute and two nostrils came along for the ride.

The other advantage could be more turbinate surface which filters inhaled air.

If we assume a point source for smells and still air, dual nostrils will provide directional smelling, as smells to either side of the animal will concentrate more in one nostril.

Human experience is probably inapplicable to this; our sense of smell is weak and our nostrils are too close together to provide adequate parallax.

The forked tongues of snakes seem like a good case for the directional smelling hypothesis though; why would forked tungues, which previously were a single, un-forked tongue, evolve unless the change promoted increased directionality of the Jacobson's organ?

Skeptic Ginger
3rd November 2007, 07:40 PM
From here: (http://www.abc.net.au/science/k2/moments/s198395.htm)



Another interesting fact:"Is your nose normally that size or are you just glad to see me?":DThis is great. But I offer an alternative conclusion about the 3D smelling.

First, here is the source of Rasmus' vague memory:It seems that in some people, the erectile tissue in one nostril will swell, while at the same time, in the other nostril, it will shrink. So while one nostril is passing a lot of air, the other isn't. And then a little bit later it swaps over. The complete Nasal Cycle takes anything from 40 minutes to several hours to run. Only a small number of people have the classical "one nostril with good air flow while the other one has bad air flow", with a regular rhythmical changeover. But most of us have some degree of rhythmical change of air flow from one nostril to the other. This is called the Nasal Cycle. It seems that this Nasal Cycle gets weaker as you get older.That makes sense as long as you don't add in the one nostril is blocked then the other and as long as you don't add the part about it being in response to one's stuffed up nose.

Then there is this info and conclusion:Now if you look at the odour chemicals that land on your olfactory epithelium, you can break them down into two types - the ones that dissolve quickly, and the ones that dissolve slowly.

The ones that dissolve slowly have their maximum effect in the nostril which has a slow movement of air. This gives time for the slow-dissolving chemicals to absorb into the mucus covering the olfactory epithelium. But if the air is moving fast, they get whisked over the olfactory epithelium before they get a chance to dissolve.

The story is completely reversed for the chemicals that dissolve quickly. They have their strongest effect when they're in an air stream that's moving quickly. In this case, they get to land on a large area of olfactory epithelium, and stimulate your brain more. But when they're in an air stream that's moving slowly, they all dissolve immediately in just a little patch of the olfactory epithelium.

Now we're not sure exactly what advantage there is in having the airflow different in each nostril. But the authors of this paper offer their theory. If, thanks to the Nasal Cycle, one nostril is passing lots of air and the other is passing less air, then the same chemicals drawn into each nostril will give different responses in each nostril. This "stereo" smelling ability will let you interpret the outside world better.All is well until the conclusion. Unless I am just having a logic block, I see no way the brain would have of determining direction by such a process. And the fact the function alternates between sides makes it even more curious. That is until you factor in attenuation.

Nerves exposed to the same stimuli continually stop responding to it. This doesn't happen with sight and hearing because the input continually changes. But exposure to touch, heat, cold and so on produce the specific neuron to fire. If the exposure continues, the sensation attenuates and you get used to whatever and the sensation changes.

I'm sure most of us have experienced a smell which is strong at first then hard to detect soon after. But leave the area and come back, and you can smell it again. Kids do nerve attenuation experiments in high school science classes. Maybe some of you did them using frogs' legs?

So the system of alternating olfactory nerves could overcome attenuation.

If someone wants to explain just how that 3D smell was supposed to work, I'm open. But to have 3D you need two equal receptors comparing input from two sides. One 'sees' the input differently than the other. What this science is describing is two sides 'seeing' two different things, not two versions of the same thing.

Skeptic Ginger
3rd November 2007, 08:02 PM
If we assume a point source for smells and still air, dual nostrils will provide directional smelling, as smells to either side of the animal will concentrate more in one nostril.

Human experience is probably inapplicable to this; our sense of smell is weak and our nostrils are too close together to provide adequate parallax.

The forked tongues of snakes seem like a good case for the directional smelling hypothesis though; why would forked tungues, which previously were a single, un-forked tongue, evolve unless the change promoted increased directionality of the Jacobson's organ?I'm going to continue out on my limb here (which I feel is not only still secure, the above reference to the nostril cycle actually supports my conclusions).

Compare the difference in a forked tongue and inhaling odorous chemicals into your nostrils. Why is the snake's tongue forked? (http://www.sciencemag.org/cgi/content/abstract/263/5153/1573)The ability to sample simultaneously two points along a chemical gradient provides the basis for instantaneous assessment of trail location. The snake actually collects the chemical sample then transfers it to the two openings of its Jacobson's organ, the organ of smell in a snake.

Inhaling, on the other hand, instantly affects the location and concentration of the chemicals in the vicinity of the nose since the chemicals are molecules in a gas state. If more air goes in one nostril, so will more chemical. The snake takes a sample of the gas from two locations without first disturbing the gas cloud. Inhaling immediately disturbs the gas cloud making 3D smelling impossible.

See also what I said above on this. Where are the animals with widely separated nostrils and the related behavior indicating the use of 3D smelling? The reptile's forked tongue is one mechanism of 3D smell. But the nostril isn't. And the nostril cycle described above is even more reason to discount the 3D smell hypothesis.

alfaniner
3rd November 2007, 08:07 PM
The better to make snot rockets with, my dear!

Seriously though, this is one of the more intriguing questions, and threads, I've encountered in a while!

Walrus32
3rd November 2007, 08:17 PM
We have stereo hearing and stereo vision because the signals reaching our ears and eyes come rapidly - 1100 feet per second for sound, and somewhat faster for light, as I recall. The capacity to quickly locate the source of those signals would impart a definite survival advantage.

Odors reach us through the gentle wafting of breezes. If stereo olfaction had a survival advantage, we would have evolved to breathing through our ears. Instead, our sense of smell is about dead center in our head, in the cribriform plate.

Of interest also is the fact that humans can't hear stereo underwater, where the velocity of sound is about 4900 feet per second. Our ears aren't far enough apart.

neutrino_cannon
3rd November 2007, 08:17 PM
Since paired nostrils obviously have no or negligible directionality in human smell, I think we can agree that it would be most useful to look at ancestral forms to determine what role, if any, nostrils have in smell directionality.

In fact, therapsids ancestral to mammals and more basal than cynodonts lacked a secondary palate (or at least and ossified one, and the absence of a secondary palate was basal at some point) meaning that the primary means of breathing would be the mouth. With the airflow being thus much less disturbed around the nostrils, directional smelling seems to me a still viable hypothesis.

Edit:

Huh. (http://www.springerlink.com/content/g66xq24w11644772/) Maybe human smell is directional after all.

Skeptic Ginger
3rd November 2007, 08:32 PM
Since paired nostrils obviously have no or negligible directionality in human smell, I think we can agree that it would be most useful to look at ancestral forms to determine what role, if any, nostrils have in smell directionality.

In fact, therapsids ancestral to mammals and more basal than cynodonts lacked a secondary palate (or at least and ossified one, and the absence of a secondary palate was basal at some point) meaning that the primary means of breathing would be the mouth. With the airflow being thus much less disturbed around the nostrils, directional smelling seems to me a still viable hypothesis.I can buy that as long as the collection of the odors is not via active inhaling. Sampling the air such as the forked tongue most certainly seems to be directional.

I would also hypothesize that 3D smelling is only needed if you can't spare the energy or don't have the mobility to wander around a bit testing air samples further apart than the distance across one's face. For a snake sneaking up on a rodent, then sampling the air from two sites a centimeter apart makes sense. It makes no sense for an animal which can simply move a few feet in different directions and get a more accurate bearing on the location of the source of an odor.

For vision, 3D is needed for hunting. Wider monovision is better for prey. What would 3D smell do for you? Perhaps you could turn your head and sniff the correct direction the first time instead of testing both directions? Seems to be of limited benefit for most mammals.

articulett
3rd November 2007, 08:47 PM
I think it allows for better breathing of a mammal snuggled up to it's mothers teat.

Skeptic Ginger
3rd November 2007, 08:48 PM
That's a good hypothesis, arti.

articulett
3rd November 2007, 08:59 PM
That's a good hypothesis, arti.

It occurred to me when my infant son had a cold... When a human baby is nursing, one nostril is usually covered...but that other little open nostril seems to make the whole system work fine.
Spare parts (kidneys, eyes, ears) can make a huge difference.

Soapy Sam
4th November 2007, 04:27 AM
The question really is "why are so many animals bilaterally symmetrical?", which I'd guess goes deep into very old HOX genes. Somewhere in there is a "rinse and repeat" loop.

As for why the two nostrils have not fused into one, I guess a tubular single nostril could develop at some embryonic stage, but the growth / timing constrains it not to. We only have one urethra, because the cells form a tube. In about 3% of men, embryological growth rates go awry and produce a tube that opens in the wrong place (Hypospadias). I wonder if there are cases of people with a split (double) urethra?

four elevener
4th November 2007, 07:42 AM
Why not three or more nostrils?

Way too many boogers to pick.

Paulhoff
4th November 2007, 03:00 PM
Because we don't have just one.

Paul

:) :) :)

Why does red look red.

Schneibster
4th November 2007, 03:56 PM
Come ON, I thought we were better than this.

So we can breathe, of course.

JJM
4th November 2007, 03:57 PM
The answer is simple: one is not enough, and three are too many. Duh...

Soapy Sam
4th November 2007, 05:18 PM
Why does red look red.

To be annoying.

articulett
4th November 2007, 05:22 PM
Actually--3 are too many... all orifices into the body are potential vectors for bad things so they evolve various protective mechanisms... so bodies tend to do a cost benefit analysis... 3 or more would have to be enough of a benefit to be worth the extra pathogen entry ways to evolve... One eye is infinitely better than no eyes--so a spare is damn useful-- 3 eyes is not infinitely better than 2. Eyes tend to evolve away when creatures live deep in the ocean or go underground because they are liabilities to maintain.

But bilateral symmetry seems to be the norm with cost benefit directing the process...

Paulhoff
4th November 2007, 05:24 PM
Let's ask the eight eyed spider.

Paul

:) :) :)

Skeptic Ginger
4th November 2007, 05:29 PM
...

Why does red look red.Are you sure it does? ;)

Paulhoff
4th November 2007, 05:33 PM
Are you sure it does? ;)
Well, what makes you think that the way I see red is the same as you do.

Paul

:) :) :)

TX50
4th November 2007, 05:49 PM
Wow, you must look ugly. Where is your nose located, exactly? ;)

I have one nose placed on the centreline of my body. I have two nostrils,
each one placed symmetrically either side of that centreline. :rolleyes:

It would perhaps be more accurate to say that I have two nasal passages which
merge into the same centrally located structure.

Jeff Corey
4th November 2007, 06:01 PM
Well, what makes you think that the way I see red is the same as you do.

Paul

:) :) :)
That's an old question in psychology, stressed by the theoretician Cantor. His answer was "Intersubjectivity". We learn to label certain sensations and get general agreement about what to call them.
And then there's Dalton, who was one of the first scientists to describe color blindness.

Paulhoff
4th November 2007, 06:18 PM
We learn to label certain sensations and get general agreement about what to call them.
Now, try to get a lot of people to understand that.

Paul

:) :) :)

Soapy Sam
5th November 2007, 04:59 AM
What makes anyone think I mean the same thing by "mean the same thing" that they do?

This way lies madness .

DavidS
5th November 2007, 05:01 AM
I think it allows for better breathing of a mammal snuggled up to it's mothers teat.
Interesting hypothesis, but not very applicable to all those non-mammals whose nostrils are also paired.

MG1962
5th November 2007, 05:05 AM
I thought it was just keep our eyes further apart

Rasmus
5th November 2007, 05:11 AM
What makes anyone think I mean the same thing by "mean the same thing" that they do?

This way lies madness .

I don't understand what you mean.

sphenisc
5th November 2007, 06:09 AM
Are there any mammals with one nostril?


Depends on how much cocaine they've used.

Dogdoctor
5th November 2007, 11:50 AM
Mysticetes (Humpbacks, Blues, Gray's, Bowheads, Rights etc) all have
two "nostrils". Odontocetes (Sperm whales, Dolphins, Bottlenose whales etc)
have one (the other having evolved into part of their echolocation system).

I would think that the reason you have two is purely to do with the way
bilaterally symmetrical bodies are constructed. One of everything down the
middle, two of everything down the outside.

This would be my guess also. It's just a result of embryological symmetry.

stevea
5th November 2007, 05:21 PM
Let's ask the eight eyed spider.

Paul

:) :) :)


Despite the number of eyes, spiders are notoriously bad at developmental biology.

Of course mammals have a high degree of bilateral symmetry. In all likelihood we don't need to all the mirror image stuff as an evolutionary advantage, but neither is it a significant disadvantage. Two eyes, two feet, two kidneys make a lot of sense functionally. Two brain-halves, two lungs, two nostrils and even two symmetric arms are not strong functional requirements. Most likely these are artifacts of the symmetry that begins very early in development. It's reinforced by visual sexual attraction issues of preferring this sort of symmetry. One spleen and one distributed liver are a happy compromise. I don't greatly care about the number of nostrils, but why the heck DON'T humans have two hearts ? (cost too high I suppose).

Paulhoff
5th November 2007, 06:21 PM
Despite the number of eyes, spiders are notoriously bad at developmental biology,
Yes, very bad, will most likely be around long after our developmental biology is gone, yes a very bad biology.

Paul

:) :) :)

And they don't pollute either, very bad.

Rasmus
6th November 2007, 08:54 AM
but why the heck DON'T humans have two hearts ? (cost too high I suppose).

Isn't the heart already dual in itself (4 chambers, two big and 2 small)?

Paulhoff
6th November 2007, 04:10 PM
Isn't the heart already dual in itself (4 chambers, two big and 2 small)?
Started out as one, two, then three before it got to 4.

Paul

:) :) :)

stevea
15th November 2007, 07:07 AM
Yes, very bad, will most likely be around long after our developmental biology is gone, yes a very bad biology.

Paul

:) :) :)

And they don't pollute either, very bad.

That's expressed biology, NOT a *knowledge* of developmental bio.

Spiders pollute - what are you thinking ? They produce CO2 - the notorious greenhouse gas. They consume and exude a good deal of nitrogen rich protein which is in part responsible for eutriphication. They are several steps up the food chain so they make very inefficient use of natural resources and primary food stuffs. D*mn little buggers.

Cuddles
15th November 2007, 07:28 AM
Started out as one, two, then three before it got to 4.

Paul

:) :) :)

It started out as one and then two. I'm not convinced about three though.

Paulhoff
15th November 2007, 07:38 AM
It started out as one and then two. I'm not convinced about three though.
Reptil Hearts

http://library.thinkquest.org/C003758/Development/reptile.htm

Paul

:) :) :)

Evolution again shows up.

stevea
15th November 2007, 07:42 AM
Started out as one, two, then three before it got to 4.

Paul

:) :) :)

I suspect it had to "start out" as two chambers to prevent backflow, even a snail has two chambers,but no matter.

My point is missed. You have two eyes and can survive at a deficit with one. You have two kidneys and can survive at a modest deficit with one. You won't survive long missing a single defective heart chamber or valve. There is no redundant functionality; it is merely a more efficient single pump and NOT two pumps or two hearts.

Some invertebrates have two hearts and can survive the loss of one. Multiple distributed hearts to might be a great advantage to some very large size high metabolism creatures, dinosaurs and whales for example, but it didn't happen.

Actually the

Paulhoff
15th November 2007, 07:43 AM
That's expressed biology, NOT a *knowledge* of developmental bio.

Spiders pollute - what are you thinking ? They produce CO2 - the notorious greenhouse gas. They consume and exude a good deal of nitrogen rich protein which is in part responsible for eutriphication. They are several steps up the food chain so they make very inefficient use of natural resources and primary food stuffs. D*mn little buggers.
How do you go from many eyes to POLLUTE.

First to pollute with Carbon (CO2), one must add new carbon to the environment, how does the spider do that.

Paul

:) :) :)

Cuddles
15th November 2007, 07:45 AM
Reptil Hearts

http://library.thinkquest.org/C003758/Development/reptile.htm

Paul

:) :) :)

Evolution again shows up.

Cool. So it went one, two, three and a half, four. Interesting that crocodiles have four complete chambers, despite being one of the least changed species still alive. If God did design all this he must have a really warped sense of humour.

Dogdoctor
15th November 2007, 01:48 PM
Still the basic thing is you start with symmetry and that continues unless there is some advantage of asymmetry that is selected for.

Paulhoff
15th November 2007, 04:22 PM
http://www.neuropsychologyarena.com/books/Handedness-and-Brain-Asymmetry-isbn9781841691046

There are many good reasons for Asymmetry.

Paul

:) :) :)

aofl
15th November 2007, 06:39 PM
Because in case if you lose one you can still have children.

Oh, you said nostrils.

Never mind.

A

Jeff Corey
15th November 2007, 07:03 PM
Cool. So it went one, two, three and a half, four. Interesting that crocodiles have four complete chambers, despite being one of the least changed species still alive. If God did design all this he must have a really warped sense of humour.

She's funny that way.

quarky
16th November 2007, 09:00 AM
we're not done evolving?
dual nostrils are an intermediate oddity?
wisdom teeth are evolving out.
deviated septums are on the rise.

i'd like to have one nostril that emerged at the top of my head, to facilitate easier swimming.

(and to attract women)

NobbyNobbs
16th November 2007, 09:06 AM
Why not 3 arms?


Why not 3 legs? A tripod is quite stable. Larry Niven did it with Peterson's Puppets in Ringworld.

As long as we're talking about strange biological features, I feel compelled to tell one of my favorite jokes...


Q: Why does the crack in your butt go up and down instead of side to side?

A: So when you go down the sliding board, it doesn't go "Fwubba fwubba fwubba fwubba"!

(Lots of hand-waving up and down during the punchline helps.)

Steve
16th November 2007, 03:05 PM
re the OP:

Their current main purpose appears to be to keep my 15 month old son amused. :D We have two so that he can use two fingers at once. I am hoping that this is a phase that he will soon grow out of.

biomorph
17th November 2007, 04:56 AM
re the OP:

Their current main purpose appears to be to keep my 15 month old son amused. :D We have two so that he can use two fingers at once. I am hoping that this is a phase that he will soon grow out of.

Is that an inherited trait?

biomorph
17th November 2007, 05:00 AM
i'd like to have one nostril that emerged at the top of my head, to facilitate easier swimming.

(and to attract women)

gosh, what sort of women do you fall for?

:jaw-dropp

biomorph
17th November 2007, 05:06 AM
Let's ask the eight eyed spider.

Paul

:) :) :)

i'm not sure of my facts here, but I thought that spiders have two eyes that are much more developed for sight than the other six, the six being somewhat redundant for sight?

if not , then fair enuff

Badly Shaved Monkey
17th November 2007, 05:21 AM
Other than being a boon to the nosering industry, what is the advantage of two nostrils rather than one big one? Are there any mammals with one nostril?

If all or most mammals are so equipped, there must be some advantage in having two. Do we possibly smell in "stereo" as an aid in determining directional source of odors?

Why Do We Have Two Nostrils?

No one seems to have made the obvious point: because we have two index fingers. It is clearly optimised for effective picking.

Rrose Selavy
17th November 2007, 06:23 AM
I sure it's been alluded to but as I understand it , smell is one of the most primitive yet most sensitive senses - we only need a very few particles in the air to detect smell as humans and of course other mammals are even more sensitive.
The eyes are very close to the brain even an extention of the brain in some ways and each left right visual fiield of each eye split to each hemisphere. Unsure if any split occurs with smell but I doubt it..
As smell has had longer to evolve, and is "older" than eyes, maybe as mentioned a pair became yet more useful and the norm.

Paulhoff
17th November 2007, 07:05 AM
i'm not sure of my facts here, but I thought that spiders have two eyes that are much more developed for sight than the other six, the six being somewhat redundant for sight?

if not , then fair enuff
They are still far better then the spider's legs for detecting light.

Paul

:) :) :)

biomorph
17th November 2007, 08:18 AM
They are still far better then the spider's legs for detecting light.

Paul

:) :) :)

that, of course, is true. Missed that one, my apologies
:eye-poppi

stevea
20th November 2007, 06:55 AM
I sure it's been alluded to but as I understand it , smell is one of the most primitive yet most sensitive senses - we only need a very few particles in the air to detect smell as humans and of course other mammals are even more sensitive.

The sorts of chemicals which have the lowest sensory threshold for humans (things like skunky mercaptans) require concentrations of about 10^-11 to be detected or roughly 10 billion to 1 trillion molecules in a 1 liter whiff. That's more than "a very few particles".

===
First to pollute with Carbon (CO2), one must add new carbon to the environment,

The reference to pollution was a response to *YOUR* post, Paulhoff.
All fossil fuel carbon was once in the atmosphere, so by Paulhoff's definition burning coal isn't pollution.

Yes, converting plant matter into gaseous atmospheric CO2 rather than leaving it in a sequestered form can be considered pollution. A common definition of "weed" is a plant growing where the gardener does not wish it. "Pollution" is a similarly anthropomorphic term; only has meaning wrt human intention.

Cuddles
20th November 2007, 08:28 AM
The sorts of chemicals which have the lowest sensory threshold for humans (things like skunky mercaptans) require concentrations of about 10^-11 to be detected or roughly 10 billion to 1 trillion molecules in a 1 liter whiff. That's more than "a very few particles".

However, there are 26.9e18 molecules in a liter of air (at stp). Those 10 billion molecules amount to less than 1 part per billion. That's generally considered "very few" by any reasonable standard. When it comes to molecules it's not really fair to talk about absolute numbers, it's the concentration that matters.

Paulhoff
20th November 2007, 08:46 AM
The reference to pollution was a response to *YOUR* post, Paulhoff.
All fossil fuel carbon was once in the atmosphere, so by Paulhoff's definition burning coal isn't pollution.
Nothing like being missquoted, you know what I mean, or you are the one with an understanding problem.

Paul

:) :) :)

stevea
26th November 2007, 05:18 PM
However, there are 26.9e18 molecules in a liter of air (at stp). Those 10 billion molecules amount to less than 1 part per billion. That's generally considered "very few" by any reasonable standard. When it comes to molecules it's not really fair to talk about absolute numbers, it's the concentration that matters.

A mole of gas is 6*10^23 molecules at STP and occupies 22.4 liter at STP, to 1L has ~2.7*10^22 molecules =27e21 (not 26.9e18). Your figure is for 1 MILLIliter.

Would you please loan me "a very few" pennies by YOUR definition I'll retire on the interest. :jaw-dropp . Your definition of "very few" needs revision. That was my only point, and I'll stand by it.

stevea
26th November 2007, 05:56 PM
Nothing like being missquoted, you know what I mean, or you are the one with an understanding problem.

Paul

:) :) :)


No dice Paul. You were NOT misquoted. If you believe otherwise then I'll trouble you to point to the EXACT "misquote" (a quote is one of those things in double-quotes or grey-box). If you can then I'll gladly apologize to the extent it effects the interpretation of your proposition. Otherwise I'll judge that you are just throwing out rude nasty accusations to save face.

The original reference to spiders and "pollute" was in YOUR post #52. Read 'em & weep.

Paulhoff
26th November 2007, 06:36 PM
No dice Paul. You were NOT misquoted. If you believe otherwise then I'll trouble you to point to the EXACT "misquote" (a quote is one of those things in double-quotes or grey-box). If you can then I'll gladly apologize to the extent it effects the interpretation of your proposition. Otherwise I'll judge that you are just throwing out rude nasty accusations to save face.

The original reference to spiders and "pollute" was in YOUR post #52. Read 'em & weep.
The weep is yours, a spider does not add to the carbon in the current environment total, burning coal etc does add to the current environment total.

Paul

:) :) :)

Cuddles
27th November 2007, 05:21 AM
A mole of gas is 6*10^23 molecules at STP and occupies 22.4 liter at STP, to 1L has ~2.7*10^22 molecules =27e21 (not 26.9e18). Your figure is for 1 MILLIliter.

Good point. Not sure where I lost the thousand.

Would you please loan me "a very few" pennies by YOUR definition I'll retire on the interest. :jaw-dropp . Your definition of "very few" needs revision. That was my only point, and I'll stand by it.

Unfortunately for you, you're correction shows that rather than one part per billion, it is actually one part per trillion. I'm entirely happy to loan you one trillionth of my money. You may want to wait a few lifetimes of the universe for the interest to actually make it worth anything though. Sounds like "very few" to me.