BBC六分钟英语｜为什么有些动物是黑白相间的？

Why are some animals black and white?

Neil
Hello. This is 6 Minute English from BBC Learning English. I'm Neil.

Becca
And I'm Becca. Neil, what do the following animals have in common? Zebras, giant pandas and magpies.

Neil
That's pretty easy, Becca. They're all black and white.

Becca
Right! But do you know why these animals evolved to be black and white?

Neil
Hmm. I'm not so sure. Probably something about survival.

Becca
That's usually the answer, isn't it?

Neil
It is.

Becca
The animal world is full of colour – shiny blue peacocks and bright green frogs. But in fact, hundreds of animal species are black and white. In this episode, we'll try to find out why, while also learning some useful new words and phrases.

Neil
OK. Time for a question for you, Becca. According to one theory, some animals are black and white to warn potential predators that they're dangerous or they taste bad. But what is the scientific term for this? Is it: a) camouflage, b) mimicry, or c) aposematism?

Becca
Well, Neil, I'm going to go with c) just because I've never heard of that word before.

Neil
OK. I like... I like your style! Some scientists think zebras' distinctive black-and-white stripes prevent bites from flies and other insects. Zoologist Dr Martin How tested this theory by covering horses, a close relative of the zebra, in stripes. Here, Martin discusses his experiment with Caroline Steel from BBC World Service programme CrowdScience:

Caroline Steel
Do we know what it is about the stripes that's putting them off? Is it somehow, like, visually confusing?

Dr Martin How
We originally set out to test whether maybe there were these optical illusions at play, so we did a whole bunch of tests where we tried different patterns of rugs, but it turned out that practically every high-contrast pattern, every black and white pattern we used, almost every pattern was really effective at stopping flies.

Becca
Martin conducted a whole bunch of – meaning a lot of – tests using different colours and patterns. Black and white stripes created an optical illusion, a visual trick that makes your eyes see things differently from how they really are. As a result, the flies were put off. They lost interest and didn't bite.

Neil
So, zebras' stripes confuse insects, telling them to look elsewhere for food. But are there other reasons animals are black and white?

Becca
Nobody who's seen giant pandas in a zoo would find them hard to spot. Against a grassy background, they stand out easily. But seen from a distance in the snowy mountain forests where they live, black and white makes the perfect disguise.

Neil
Here's Professor Tim Caro, a world authority on animal behaviour, explaining more to Caroline Steel for BBC World Service's CrowdScience:

Professor Tim Caro
The giveaway for me was 15 photos of giant pandas, taken either fairly close up or at a distance, and in two of those photos, I was unable to see anything in the picture other than rocks and snow. And then later on, I realised that in fact there was a giant panda in the centre of that picture some distance away. Immediately that... that clicked in my mind.

Becca
The pandas were so well camouflaged Tim couldn't spot them in the photos. That's when something clicked in his mind – a phrase used when you suddenly understand something after trying for a long time.

Neil
Tim understood that pandas use colour to hide. He calls this a giveaway – something that makes it easy for people to discover something secret or unknown.

Becca
So, are animals black and white to repel insects, like zebras, or for camouflage, like pandas? Let's give the final word to Hannah Rowland, a researcher into another black and white animal – penguins.

Hannah Rowland
Really, science never has a black-and-white answer – excuse the pun – about the... with penguins being black and white. It's often a very complex mixture of reasons.

Neil
The answer to why animals are black and white is not black and white – a situation described as black and white means one where it's easy to understand what's right and wrong.

Becca
In fact, there's no one reason why animals are black and white. Zebras avoid bites, pandas hide from predators and some animals, like skunks, warn other animals they're dangerous. It all depends on the specific animal.

Neil
And talking of skunks reminds me of my question, Becca. According to one theory, some animals are black and white to warn potential predators they're dangerous or taste bad. But what is the scientific term?

Becca
And I chose c) aposematism because I'd never heard of it before.

Neil
Well, that's a great way of choosing. And it's done well for you because you're correct.


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