I'm asking this question on this website because I want an evolutionary reason rather than a reason of how the human brain works. In one episode of "The Nature of Things," I heard David Suzuki say he was terrified when he went in a deep mine because he's afraid of depths rather than because of the higher temperature there, so I assume other people feel the same way. I'm also scared to go into a submarine that will go really deep into the ocean because I know the laws of Physics and realize that there might be a mistake and it's not as strong as the designers thought and it might implode under the extreme outside pressure. Maybe for some people, it's a fear for a good reason like me and for other people, it's a fear for no reason. I want to know a reasonable theory on what the evolutionary reason for it is. Is it similar to the reason why the human selection of nonaggressive dogs led to dogs with floppy ears? I think it was so rare for somebody to be able to kill themselves with depths by implosion that the fear of depths wasn't selected against directly. For example, in our evolutionary history, by the time somebody swam deep enough that they could not swim back up to the surface without drowning first, the pressure still wasn't extreme enough to implode their lungs. I think that instead, there were many ways people could kill themselves but there was also a pattern between the different ways they could kill themselves so it was easier for them to evolve a simpler way to avoid killing themselves in any of those ways, and although death by being crushed under extreme pressure at great depths wasn't one of the ways, it fit into the pattern of the other ways people could kill themselves so the natural selection for people who don't kill themselves those other ways came with the trait of fear of depths automatically. Could the fear have actually been selected for directly after all because people could not think ahead and by the time they've swum to the deepest depth they can and still make it back to the surface, they're like "I still don't yet have the desperate urge to breathe so I can swim even deeper" so instead, natural selection selected for people who were afraid of swimming that deep below the surface of the water?

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    $\begingroup$ Your question asks “why” but assumes that the answer has something to do with evolution. There seems no justification for this. The idea that every human trait has been selected for is unscientific. This question can only have subjective answers and is off-topic in my opinion. $\endgroup$ – David Jan 23 at 8:16
  • $\begingroup$ @David: Especially when the question asks about specific phobias, since there are so many different ones. Maybe a question on the mechanism of phobias in general, and whether they exist in other species? $\endgroup$ – jamesqf Jan 23 at 18:07
  • $\begingroup$ Surely you know the evolutionary reason for an organism to be afraid of things that might kill them. Humans have this loosely controlled brain that comes up with all kinds of ideas, right or wrong, and will assess that some of them can kill them. $\endgroup$ – mgkrebbs Jan 23 at 19:41
  • $\begingroup$ @mgkrebbs: But 1) People may have phobias about things that many people consider to be perfectly harmless, or even desireable, as for instancy cynophobia, or the fear of dogs; 2) Being cautious about things that might harm or kill you is rational - I wouldn't spend too much time around depths without safety gear myself - but the irrational, paralyzing fear of a phobia would seem to be contra-survival. $\endgroup$ – jamesqf Jan 24 at 3:08

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