Guys, I do nose breathing too, and believe in some benefits, but I don’t believe that’s what the nose evolved for. Note, that nasal pasages appear in a huge variety of animals, mammals, birds, reptiles amphibians, fish and so on. The anatomy/morphology of these passages is quite different across the animal kingdom, which tells you that most of these “reasons” listed are unlikely to be the key drivers of evolution, as they don’t appear consistently in all these animals, while nasal passages do. The connection between lungs and nose is not at all the key here - after all, there are no “lungs” as such in fish, yet fish have nasal passages and the nose therefore functions quite differently in that connection. What appears consistently is something extremely obvious yet not mentioned: the sense of smell. I think that’s probably like 90% of the reason for the persistence of a nose through evolutionary history. A fish, like a shark, can detect the presence of blood in the water in extreme dilution at great distances. It’s the sense of smell, detecting airborne or waterborne molecules that are the fundamental reason for the existance of the nose and nasal passages. Things like moisture, filtration and temperture control are certainly factors, especially in mammals, but the sense of smell is going to be the real driver. A dog in the wild, a cat, an antelope and so on, all need their sense of smell for their very survival - all the other things mentioned, like the use of diaphragm, are far, far, far down the hierarchy of function, if they are even factors at all.
That said, to me the biggest factor in nose breathing is the restriction of airflow - in exercise, it likely has a very good training function for the cardio-pulmonary system and the use of oxygen, especially in hypoxia. Athletes sometimes even use devices to restrict their breathing, which intentionally put a strain on their lungs, diaphragm muscles etc. At night, you need to breathe through the nose so that you cut down on the danger of dry mouth, because dry mouth leads to a host of dental problems (methmouth is equal parts teeth grinding and dry mouth), when teeth and the gingiva are not bathed in saliva, nasty bacteria proliferate. So I’m there for all the advantages of nose breathing, but let’s not lose sight of the key reason for the nose: the sense of smell and moisture retention in the mouth (much more than moisture in the lungs). I have not read any books about nose breathing, but listened to a podcast (I think it may have been on Attia’s podcast?), and there does seem to be science behind it, so I was happy to adopt it. Regardless, it seems that many people experience benefits, and that’s all that matters!
