Have you ever held a flickering firefly in your hands? On a warm summer evening, a firefly’s light seems rare and magical. Yet the tree of life is spangled with organisms that blink, glow, flash, and glitter. Welcome to the world of bioluminescence—the generation of light by living things.
The light we know best—incandescent light—is associated with heat. Bioluminescence, on the other hand, is cold light. So what creates bioluminescence? A reaction between two chemicals—luciferin and luciferase.
Some creatures manufacture their own light-making chemicals. Many more get their chemicals from the organisms they eat. A few “borrow” their light by forming partnerships with glowing bacteria. And others fluoresce rather than luminesce; they absorb one color of light and emit another.
Eighty percent of all bioluminescent groups inhabit the world’s oceans. At certain depths, nearly all the organisms glow. On land, things are quite different. There are bioluminescent fungi and insects, but no flowering plants, birds, reptiles, amphibians, or mammals that glow.
How did the ability to produce light evolve? Scientists are still working on this question. But one thing is clear: bioluminescence has evolved independently many times—at least 100, and probably many more.
Such a widespread occurrence tells scientists that the trait provides an important edge to organisms that have it. Benefits range from attracting mates, to luring prey, to warning away predators.