[engineer_22]

> This can occur in enclosed spaces like caves where some other gas-mix has excluded the oxygen

Maybe this why some people innate fear of caves, primordial adaptation for suffocation avoidance behavior. I don't know, just fun to wonder about things like that

[Terr_]

I would wager a much-bigger feedback loop involves the other things that would like to live in those caves, and the odds you might get into conflict with their jaws/claws/stingers.