Scientists have long been unable to conclude why zebras have their characteristic black-and-white stripes, until now. After analyzing five hypotheses, a team of scientists at the University of California, Davis, has determined that zebras’ stripes protect them from biting flies.
Scientists believe the zebras evolved to have stripes to deter biting flies and avoid contracting diseases from them. “It settles the question pretty well, in terms of trying to understand the evolution of striping in horses, zebras, and asses,” Tim Caro, biologist at UC Davis, told NBC News. The reason zebras developed the stripes and other hoofed animals did not is because the zebras needed them more. Because of their short hair, they are more likely to be targeted by tsetse flies and horseflies. “It’s clear that the flies can get through that hair and get to the skin,” Caro, lead author of the study, said.
Over the years, there have been many other hypotheses proposed about the stripes. Some said they were a form of camouflage, disruptive to predatory attack, a way of dealing with hot temperatures, and for use in courtship. All those hypotheses were systematically ruled out, and the only theory with ecological validity was the one involving flies. Biting flies present a danger to zebras and other animals by affecting weight, and milk production, as well as the more obvious loss of blood, and transmission of diseases.
The scientists came to their conclusion after carefully mapping geographic distributions of different species of zebras, horses, and asses. They noted intensity, thickness, and location of their stripes, and then compared that data to the geographical distribution of biting flies. It was through a similar process that other hypotheses were ruled out and scientists were able to determine that zebra stripes function to protect them from ectoparasite attack.
Their findings were published in Nature Communications on April 1st. Now the next mystery to solve is why biting flies aren’t attracted to striped surfaces. Caro, however, is glad to have found an answer to why zebras have stripes, “Solving evolutionary conundrums increases our knowledge of the natural world and may spark greater commitment to conserving it,” he said in a press release.