BBC 英语学习 梦想成为厨师

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Hello. This is 6 Minute English from BBC Learning English. I'm Neil.
And I'm Becca.
Neil, what do the following animals have in common?
Zebras, giant pandas and magpies.
That's pretty easy, Becca.
They're all black and white.
Right! But do you know why these animals evolved to be black and white?
Hmm. I'm not so sure.
Probably something about survival.
That's usually the answer, isn't it?
It is.
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.
And remember, all the vocabulary from this episode
is available on our website bbclearningenglish.com.
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?
Well, Neil, I'm going to go with c) just because I've never heard
of that word before.
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:
Do we know what it is about the stripes that's putting them off?
Is it somehow, like, visually confusing?
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.
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.
So zebras' stripes confuse insects, telling them to look elsewhere for food.
But are there other reasons animals are black and white?
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.
Here's Professor Tim Caro, a world authority on animal behaviour,
explaining more to Caroline Steel for BBC World Service's CrowdScience:
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.
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.
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.
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.
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.
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.
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.
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?
And I chose c) aposematism because I'd never heard of it before.
Well, that's a great way of choosing.
And it's done well for you because you're correct.
Woohoo!
OK. Let's recap the vocabulary we've learned,
starting with 'optical illusion' – a visual trick
where your eyes perceive things differently from how they really are.
'A whole bunch of something' means 'a lot of something'.
If something puts you off, it causes you to dislike it or lose interest.
A giveaway is something that makes it easy
for people to discover something secret or unknown.
The phrase 'something clicked in my mind' is used
when you suddenly understand something at last.
And finally, if you describe something as black and white,
you mean it's easy to understand what is right and wrong.
Once again, our six minutes are up,
but head over to our website, bbclearningenglish.com,
for a quiz and worksheet for this episode.
See you there soon.
But for now, it's goodbye.
Goodbye!
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