Subsequent to the penis question, What is the evolutionary mechanisn that caused homo sapiens to sport such large noses relative to the apes ? Could our diminished smelling capacity have something to do with it?
The first noses came about with H. erectus, who was not co-incidentally the first truly tropicalised human ancestor. By this I mean he was long and thin and clearly designed to radiate heat away from his body. It’s usually assumed this was because he was the first hominid to actively move around in the open all day long, rather than retiring to the patches of forest at during the hotter parts of the day and foraging on the savannas in the early morning and evenings.
The nose is designed to enable people to reabsorb moisture as it leaves the lungs, thus conserving some water, and also helps to condition the air, equalising hot or cold air with the body temperature and humidifying it before it hits the delicate lung membranes. These would have been handy tricks for an animal active in the far more variable environment of the savannas and deserts.
The nose also plays a role in modulating speech (as anyone who’s had a cold knows) and it is possible that it enabled better communication. The flaw in this theory is H. erectus apparently didn’t have the motor control necessry for fine speech.
It’s unlikely that our reduced smelling capacity is tied to the presence of a nose. Vultures and kiwis for example draw air through a long ‘nose’ and have a very acute sense of smell so there’s no particular reason why having an external nose nedd reduce a sense of smell. Humans don’t actually have a massively lessened sense of smell compared to otehr apes (though it is reduced). The trend towards being visually rather than olfactory sensory dominance has been going on in primates few a long time. There’s a limit to how much sensory input any organism can handle in a limited braincase so something has to give. With life on the open plains and the use of missile weapons eyesight and colour perecrption became more important to humans than smell and increased at its expense.
Although the nose/nasal cavities of any warm-blooded animal serve the same function they do in us as far as conserving moisture - nasal turbinate bones are found in all such animals, so that trait’s not unique to humans, especially since these structures aren’t in the “sticking-out” part of our nose but further back in the skull. Don’t know why our noses stick out though.
Yes but in apes the distance to the sinuses and turbinate bones is far less and there’s no external nose hanging out in the breeze. This means the air is going from ambient temperature and humidity to 37[sup]O[/sup] and 100% humidity immediately on the way in, and from 37[sup]O[/sup] and 100% humidity to ambient on the way out. A human nose gives the air a far longer trip in, allowing the air to be conditioned before it hits any mucous membranes and dries them, freezes them or fries them. Taking a very long deep breath through the nose on a freezing morning probably gives you some idea of how normal breathing would feel to an ape under the same circumstances. The shortened muzzles of homininds would make the problem even worse.
On the way out the nose, being cooler than the rest of the repiratory tract causes water vapour to condense out.