When Mexican tetra fish moved into darker caves long ago, they evolved to deal with the dark by becoming albino and going blind. A new research shows that the changes various cavefish  populations  went through occurred repeatedly. A massive textbook example of convergent revolution. The studys in the journal  BioMed Central Evolutionary Biology.

To determine how the dark-dwelling fish evolved their sightlessness, researchers  tested the DNA of 11 Mexican cavefish populations; they compared the genes with those of the tetra populations that lived out in the light. Originally researches had believed that all of the cave populations were descended from a single group of tetra fish that went underground and then went blind.  But the cavefish genes told a different story: the 11 populations had  five separate evolutionary origins, with different groups independently experiencing and selecting an eyeless mutation. Although the surfacing cave-dwelling fish frequently mix, interbreeding has not eradicated cavefish blindness, which means that evolution is actively selecting blindness, perhaps  because investing bodily resources in sight is a waste of energy in the dark.

Thanks for the minute for Scientific American Sixty Seconds Science, I'm Sophie Bushwick.