Why would a blind creature evolve display features?
I'm thinking of a predatory creature that lives deep inside large caves. Because this environment is so dark, the creature's eyes have disappeared through evolution since the creature relies on echolocation rather than sight. But the thing is that this creature has a large frill around its neck with small bioluminescent marks. But that got me thinking, what is its use? I mean, if the creature is blind then it surely can't use the frill to frighten other members of its species. So why would it evolve something like that?
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1 answer
The bioluminescence can be a vestige of when the creature's ancestors lived in very dim caves or caves (or other spaces) that were dark part of the time while they were awake. While they still had functional eyesight.
Plenty of species have biological traits that aren't currently needed. If there's no evolutionary advantage to not having them, they may not fade away as quickly as traits that are better off not being there (like eyes that can be a vector for infection if injured).
Once you've established that the bioluminescence is still around, it can prove itself useful in the ways other answerers have mentioned.
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