The primary purpose of the human nose is to detect scents. This is an obvious statement, as is that the primary function of the mouth is to eat. The secondary purpose of both of these features is to breath. Now Merfolk who evolve underwater would have no need for the sense of smell (as it would be replaced with taste), so would the evolution of the Merperson favor the replacement of the nose for gills?

  • $\begingroup$ the lungs are replaced (unless these merfolk are akin to lungfish), not the nose. also, have you ever seen a fish without nostrils? $\endgroup$ – XenoDwarf Jul 11 '16 at 5:02
  • $\begingroup$ a mammal can't become a fish this fast .A better system is starting to breath through the skin. $\endgroup$ – user22398 Jul 11 '16 at 5:05
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    $\begingroup$ Fishes have noses too, of more varied kinds than other vertebrates. $\endgroup$ – The Square-Cube Law Jul 12 '16 at 0:47

No. It wouldn't be favored. It would be required.

An organism with lungs and a nose cannot live underwater any more than you can. Before that point they have to evolve gills (including the "lungs"), at least in addition to land-based breathing.

edit: I think there was a misunderstanding. I am not claiming that any organism living in water needs gills (dolphins and other animals don't have them). Rather I am claiming that a human could not live in water without extensive modifications. While it would be possible to adapt the human organism in such a way as to allow it to live underwater without requiring gills, gills are the easiest solution as well as the one that constrains a writer the least (as in, if they have gills they don't need to have the merfolk surface all the time and can place them in deep water environments as well).

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  • $\begingroup$ dolphins don't have gills and can stay underwater for about 30 seconds, for them it's enough to hunt,sleep and reproduce. $\endgroup$ – user22398 Jul 11 '16 at 5:09
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    $\begingroup$ @άλεξμιζέρια sure, but that's a pretty heavy disadvantage for merfolk and one that would limit the author a lot in what they are trying to build. (30 seconds? are you sure? I thought it was 15 minutes or so...). $\endgroup$ – Annonymus Jul 11 '16 at 5:14
  • $\begingroup$ 15 minutes isn't the average for dolphins the same way 20 minutes records with pure oxygen preparation isn't the average for all humans... $\endgroup$ – user22398 Jul 11 '16 at 5:22
  • $\begingroup$ @άλεξμιζέρια I see. Thanks for clearing that up. $\endgroup$ – Annonymus Jul 11 '16 at 5:23
  • $\begingroup$ The mammalian diving reflex is an impressive adaptation. "-- the Sperm whale who frequently makes dives to about 2000 meters, and also the Elephant seal who dives to around 1500 meters. One of the most studied marine mammals is the Weddell seal who dives to about 700 meters and can stay submerged for up to a registered 82 minutes!" At thewildclassroom.com/cetaceans/adaptations.html A bit more than 30 seconds. Google diving reflex and be amazed. $\endgroup$ – a4android Jul 11 '16 at 9:23

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