https://phys.org/news/2018-07-bioluminescence-humans-nature.html

Bioluminescence, the production and emission of light by living organisms, became a sticking point for Darwin. He struggled to explain why this phenomenon appeared in separate species in a seemingly random fashion. We now know, however, that bioluminescence has evolved independently at least 40 times on land and in the sea.

Darwin was not the first to note bioluminescence. Greek philosopher Aristotle observed that bioluminescence is a type of "cold" light – in that it does not produce heat – in around 350 BC. Researchers have since found that this form of chemiluminescence, produces blue-green light as a result of the oxidation of a compound called luciferin (the "light-bringer") by an enzyme called luciferase.