英语听力精选进阶版 7238（在线收听）

There 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.

Quiz

1. True or false? There have been different explanations about why zebras have stripes.

True.

2. The latest scientific reserach shows that stripes give zebras an advantage over their non-striped ancestors. What is it?

The striped pattern makes the zebras much less attractive to insects.

3. What is the main enemy of zebras mentioned in the report?

The horsefly.

4. How different do modern-day zebras look from their ancestors?

They have black and white stripes whereas their ancestors may have looked pure black.

Glossary 词汇表

unmistakable 准确无误的

camouflage 掩体/伪装

predators 食肉动物

irritating 令人烦恼的

ubiquitous 无处不在的

horsefly 马蝇

fly-infested 充满苍蝇的

ancestor 祖先

evolved 进化

scourge 天灾/瘟疫