Why zebras evolved their characteristic black-and-white stripes has been the subject of decades of debate among scientists.
Now researchers from Hungary and Sweden claim to have solved the mystery.
The stripes, they say, came about to keep away blood-sucking flies.
They report in the Journal of Experimental Biology that this pattern of narrow stripes makes zebras "unattractive" to the flies.
They key to this effect is in how the striped patterns reflect light.
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Prof Matthew Cobb, an evolutionary biologist from the University of Manchester pointed out that the experiment was "rigorous and fascinating" but did not exclude the other hypotheses about the origin of zebras' stripes.
"Above all, for this explanation to be true, the authors would have to show that tabanid fly bites are a major selection pressure on zebras, but not on horses and donkeys found elsewhere in the world... none of which are stripy," he told BBC Nature.
"[They] recognise this in their study, and my hunch is that there is not a single explanation and that many factors are involved in the zebra's stripes.