【媒体英语】斑马为何有斑纹？

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disease-carrying
fly-infested
zebra-striped
blood-suckingThere have been many theories to explain the zebra's unmistakable stripes. Scientists have suggested that each zebra has a unique pattern that lets other animals recognise it. Or that the mass of black and white in a vast herd provides confusing camouflage that puts off predators. But this team set out to test exactly what effect the stripes had on a zebra's most irritating and ubiquitous enemy, the blood-sucking horsefly. As part of their experiment the team put sticky horse models, one white, one black and one zebra-striped into a fly-infested field. When they collected the flies that had landed and stuck to each of the models, they found that the model zebra attracted by far the fewest flies. The researchers think that zebras had a black-coated ancestor, which evolved its white stripes in an evolutionary arms race, with an insect that's become the biting, disease-carrying scourge of most horse herds.