The evolution of the human nose is a curiosity.
First I'm wondering if it coincides with the loss of the full coat of hair. Second, this idea of coincidence makes me wonder if it's an inconsequential change that rides on the same gene along with some other adaptation such as losing hair.
Some other answers I saw online were attempting to explain it as a functional change to increase warmth and moisture of the airways. That to me doesn't correlate too well with adapting away from arboreal life, or from losing hair, which indicates the protohuman was keeping warmer.
Considering the advantages of fur and the way other critters have other adaptations for seasonal and climate differences through long and short hair, shedding, etc., I was also thinking about the amount of time apes spend grooming and debugging (literally, you code monkeys
).
Loss of fur could coincide with spending more time in contact with the dirt, changes in the social structure and access to fellow nitpickers (present company excluded). If parasites and "hygiene" are a cause, then this leads to the question of how defenses against various parasites changed for the protohuman. My next thought was that of bald carrion eaters. Is it an adaptation similar to that for eating massively infested rotten meat? If so, is the nose then related to all of this in some more subtle way? It seems that the nose stores some powerful semi-beneficial bacteria (staph and strep seem to protect against other invasive forms).
Another thing I was thinking about was ground habitats such as cave dwelling. In the shade these ancestors may have needed an adaptation for exposure to dust, mites and fungal spores, without adversely impacting the advantages of the immune response. So even a slight roof over the nares could help. We seem to stand apart from animals in the wild with regard to allergies, and some indoor causes are known to plague us.
Sexual selection for a nose would amplify all of this. Maybe something as simple as having a persistent cold or allergies would hinder mating.
One last idea. When we exhale though the nose, as when eating or drinking, since it's difficult not to, there a slight back pressure which the chimps wouldn't experience. This would potentially help with sensing the quality of the thing we're eating or drinking. This goes back to the way our eating habits changed from, say, eating termites to cleaning up after a kill (in the way hyenas do after a big cat has finished or dragged away the main part of the carcass). At some point it may have been necessary to distinguish flavors and the odors of food in a way that doesn't apply to the noseless ancestor.
