Bioluminescence

Bioluminescence — the production and emission of light by living organisms through chemical reactions — is one of nature's most magical phenomena. It has evolved independently over 50 times in different lineages, making it one of the most common 'repeated inventions' in evolution. It is found in fireflies (luciferin + luciferase reaction), deep-sea fish (anglerfish's esca/lure), dinoflagellates (single-celled plankton that glow when disturbed, causing 'milky seas' and glowing waves), jellyfish, squid, bacteria, and many others. Approximately 80% of deep-sea species are bioluminescent — in a world without sunlight, light is the primary communication tool (for mate attraction, prey luring, predator confusion, and camouflage — counterillumination to match downwelling light). Aequorea victoria jellyfish's green fluorescent protein (GFP) — isolated in 1961 — became the most widely used tool in cell biology (2008 Nobel Chemistry), enabling researchers to tag and track individual proteins and cells in living organisms.