The fact that zebras are born black and only develop stripes as they grow older made the scientists theorize that the stripes may be something the animals have developed to make themselves less attractive to flies.
To test if this may be the case, they painted some boards at a horse-infested(寄生的) horse farm in Budapest with patterns of black and white stripes of varying widths and applied a layer of glue on them. What they noticed was that the places where the black and white stripes were at their narrowest (similar to what zebras have) attracted the fewest flies. They achieved similar results when they painted horses with black and white zebra-like stripes.
While the research are not sure why this may be the case, they believe it may be something to do with the way insects operate---horseflies are attracted to horizontally polarized light(偏振光); since white does not reflect it, white horses are luckier than black ones. But zebras seem to be the luckiest of all. When the researchers measured the polarized light reflected from real zebra skins, they found that it matched light patterns that were the least attractive to horseflies.
While this theory does make logical sense, nobody is 100 percent sure that it is really true, given that it has never been tested on a real zebra. If it is true, it does raise the question of why a horse, a close relative of the zebra has failed to develop stripes. The researchers believe that this could be because there are more horseflies in Africa, where zebras reside, then anywhere else in the world.
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