It's an evolutionary question that has stumped scientists for hundreds of years: Why do zebras have stripes?

Hypotheses have included mating rituals, protection from predators, camouflage and heat protection, though no evidence has backed up the claims. But in a paper released Tuesday in Nature Communications, researchers at University of California, Davis may have proven the reason: to protect the animal from disease-carrying biting flies.

“No one knew why zebras have such striking coloration,” wrote Tim Caro, lead author and a UC Davis professor of wildlife biology, in a press release. “But solving evolutionary conundrums increases our knowledge of the natural world and may spark greater commitment to conserving it.”

The biting fly explanation has long been suspected, as flies tend to avoid black-and-white striped surfaces. To find out once and for all, researchers noted the geographic distribution of zebras, horses and asses, and noted differences in zebra stripe patterns. They then overlapped the data with variables such as temperature, terrain, predator range and biting fly distribution.

While the other factors did not correlate with stripe patterns, one factor overwhelmingly did: the biting flies.

“I was amazed by our results,” wrote Caro. "Again and again, there was greater striping on areas of the body in those parts of the world where there was more annoyance from biting flies.”

Researchers noted that the short coats of zebras make them particularly susceptible to the flies, which may explain why the stripes do not appear on other animals.

However, as researchers mentioned in the release, one mystery solved leads to yet another mystery: why biting flies avoid black-and-white striped surfaces.