Why would a creature with a similar lifestyle as seals, sea-lions and amphibians-living near water and diving for food-evolve bioluminescence?

These creatures are roughly the size of a dolphin or a california sea-lion, sapient or highly intelligent and social. They live near the ocean and swim to hunt for food, and can take dives 1-3 hundred meters deep.

  • 1
    $\begingroup$ Questions asking why aren't a good fit for this site. Obviously there was something that lead to it evolving, which could be that the genes to express this provided some un-related evolutionary advantage. As written any potential reason for the trait to evolve will be equally valid. Questions with many valid answers aren't permitted on this site. Does it matter why the trait evolved? Because we don't know why most traits are developed on earth. At best we can make educated guesses about things that happened in the far past. $\endgroup$
    – sphennings
    Oct 11, 2022 at 21:04
  • $\begingroup$ Mating display. $\endgroup$
    – user73215
    Oct 12, 2022 at 15:58
  • $\begingroup$ Evolution does not have a final goal or anything. "Why" something evolved is very often answered by "because it wasn't removed through evolution". Humans have appendixes and they serve no useful purpose. They can be extremely not useful if they rupture. Why did humans evolve appendixes? Not by choice, nor utility. It was just left there. $\endgroup$
    – VLAZ
    Oct 16, 2022 at 7:42
  • $\begingroup$ But what useful purpose could bioluminiscence serve to semi-aquatic packhunters? $\endgroup$ Oct 17, 2022 at 8:46

1 Answer 1


Underwater coordination

Your creatures are pack hunters. They are primarily visual, like seals. They are not stealthy - their prey knows very well what these predators are doing.

Bioluminescence allows individuals to keep track of pack mates in the dark water and coordinate movements. That makes them more effective hunters and confers a fitness advantage.

The corollary to this - wavelengths need to be those least prone to scatter over distance and so would be long: far red. Maybe these creatures can see some way into the infrared.


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