Dive deep enough under the surface of the ocean, and light reigns. Some 90 percent of the fish and crustaceans that dwell at depths of 100 to 1,000 meters are capable of making their own light. Flashlight fish hunt and communicate with a flashing Morse code sent by light pockets that pulse under their eyes. Tubeshoulder fish shoot luminous ink at their attackers. Hatchetfish make themselves appear invisible by generating light on their underbellies to mimic downwelling sunlight; predators prowling below look up to see only a continuous glow.

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Original story reprinted with permission from Quanta Magazine, an editorially independent division of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences


Scientists have indexed thousands of bioluminescent organisms across the tree of life, and they expect to add many more. Yet researchers have long wondered how bioluminescence came to be. Now, as explained in several recently released studies, researchers have made significant progress in understanding the origins of bioluminescence–both evolutionary and chemical. The new understanding may one day allow bioluminescence to be used as a tool in biology and medical research.

One longstanding challenge has been determining how many separate times bioluminescence arose. How many species came to the same conclusion, independent of one another?

Though some of the most familiar examples of light from living organisms are terrestrial–think of fireflies, glowworms and foxfire–the bulk of evolutionary events involving bioluminescence took place in the ocean. Bioluminescence is in fact markedly absent from all terrestrial vertebrates and flowering plants.

In the deep ocean, light gives organisms a unique way to attract prey, communicate and defend themselves, said Matthew Davis, a biologist at St. Cloud State University in Minnesota. In a study released in June, he and his colleagues found that fish that use light for communication and courtship signaling were especially diverse. Over a period of about 150 million years–brief by evolutionary standards–such fish proliferated into more species than other groups of fish. Bioluminescent species that used their light exclusively for camouflage, on the other hand, were no more diverse.

Courtship signals can change relatively easily. These changes can in turn create subgroups in a population, which eventually split into unique species. In June, Todd Oakley, an evolutionary biologist at the University of California, Santa Barbara, and one of his students, Emily Ellis, published a study in which they found that organisms that use bioluminescence in courtship had significantly more species, and faster rates of species accumulation, than closely related organisms that do not use light. Oakley and Ellis studied ten groups of organisms, including fireflies, octopuses, sharks and tiny crustaceans called ostracods.

The study by Davis and his colleagues was limited to ray-finned fishes, a group that includes approximately 95 percent of fish species. Davis estimated that even in that single group, bioluminescence evolved at least 27 times. Steven Haddock, a marine biologist at the Monterey Bay Aquarium Research Institute and an expert on bioluminescence, estimated that across all life forms bioluminescence evolved independently at least 50 times.