Ouabache said:Whether recent or historic, selection pressures allow useful traits to be passed on while others are discarded. Two eyes gives us depth perception, a distinct advantage over creatures with a single eye. With this added piece of information, we can detect and escape predators with greater ease than those with one eye. We are also less likely to walk off a cliff. With only those two examples, there would be a distinct selection pressure for keeping two eyes. Similarly with our ears, we perceive direction information because our ears receive incoming sounds stereophonically. We perceive which direction a threatening predator is approaching and thereby have a better chance take evasive action over those with a single ear.
Monique raises a good point, that a single circular or oval nasal passage would also be bilaterally symmetric. Animals could have just as easily, generated this phenotypic variant. So begs the question, what benefit is there having two nostrils over a single one? For example, does it empower animals to detect food or a mate more efficiently?
Yes, that is the tendency. But it is not a rule.Ouabache said:Whether recent or historic, selection pressures allow useful traits to be passed on while others are discarded.
It is wrong to assume that everything has to be an advantage. It simply does not work that way.Ouabache said:Monique raises a good point, that a single circular or oval nasal passage would also be bilaterally symmetric. Animals could have just as easily, generated this phenotypic variant. So begs the question, what benefit is there having two nostrils over a single one? For example, does it empower animals to detect food or a mate more efficiently?
Is any of this based on fact? Where is your information coming from?vivanenko said:Without two separate airways through the nose, our sense of smell wouldn’t be nearly as sharp as it is.
Let's say you're out for a walk and you stop to sniff a flower. You inhale, and air containing tiny flower particles rushes up your nose. Sensors in the nose absorb the particles and send smell signals to the brain. Now, although they may look identical, your nostrils go through regular cycles of swelling and shrinking. When the right is swollen, the left is normal, and vice versa. The result is that the swollen nostril inhales a bit more slowly than the non-swollen nostril, which affects how quickly the flower particles reach the inside of your nose.
This is important because there are two basic kinds of smell-producing particles that enter your nose. Some dissolve slowly and others more quickly. When you sniff a flower, the slow-dissolving flower particles need time to settle down inside your nose in order to really register. Breathe them in too fast and many just pass right through without stopping to contribute to that great flowery smell. Meanwhile, the fast dissolving flower bits like to charge in and take over. Caught on a too slow air stream, these particles will dissolve before they really have a chance to make their mark.
And that's why having two nostrils comes in handy. Slowly-dissolving particles do better when inhaled through the swollen, slow breathing nostril. Fast-dissolving particles thrive when taken in through the non-swollen, fast breathing nostril. Working together, your nostrils allow you to smell both kinds of particles.