Some adaptations are super-specific; they appear once in one species and vanish, or they stay there and are passed on to that species’ evolutionary offshoots. Others are more widespread, popping up in one group of organisms, and then another, and then another. For example: Researchers say bioluminescence, or the ability to glow, has independently arisen no fewer than 27 times in fish. The team published their findings in the journal PLOS One

When we hear the words “glowing animals,” fireflies naturally come to mind. But the firefly is just one of hundreds of bioluminescent organisms. We also share our planet with sparkling squid, luminous mushrooms, radiant bacteria, and a whole bunch of glowing fish. This ability to become your own light source has all kinds of uses. Creatures use it to hunt, attract mates, communicate, or hide (and we use their bioluminescence for a variety of medical purposes). Scientists have documented that, since life began, bioluminescence has evolved at least 40 different times.

A team of researchers from the American Museum of Natural History (AMNH), St. Cloud State University, and the University of Kansas wanted to find out how many times the trait has evolved in fish alone. They reviewed genetic data from more than 1510 species of bioluminescent fish, looking for the point in each species’ history when the trait first appeared. They expected to find it popping up at a few different moments in fish history.

Instead, their results suggested that the ability to glow has evolved independently in fish no fewer than 27 times in 14 major fish clades during the past 150 million years. The fact that this amazing ability has bloomed so frequently in fish history suggests that it must be even more useful than scientists previously believed. 

“Our findings completely change how we look at the evolution of bioluminescence across all life,” AMNH ichthyologist and paper co-author John Sparks said in a press statement. “If we are seeing these kind of numbers in marine fishes alone, bioluminescence has evolved far more than 40 times across the tree of life. This suggests that we need to take a closer look at the evolution and diversification of other lineages with bioluminescent members.”