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Hi everyone!
各位好！
You got here just in time for a story!
来得正好，听个故事吧！
It's a great one — and it's about something that really happened.
这是一个很棒的故事，讲述的是真实发生的事情。
This is the story of the Peppered Moth.
这个故事关于胡椒蛾。
A long time ago, most peppered moths had white or gray wings with little dots on them.
很久以前，大多数有斑点的蛾子的翅膀是白色或灰色的，上面有小点。
That's why people called them “peppered,” because the dots kind of look like pepper.
这就是为什么人们叫它们“胡椒”，因为这些点看起来有点像胡椒。
Instead of sleeping at night like we do, these moths are awake at night and sleep during the day.
这些蛾子不像我们那样晚上睡觉，它们晚上醒着，白天睡觉。
While they're sleeping, they like to hang out on trees.
胡椒蛾睡觉时喜欢挂在树上。
In some parts of the world, they spend lots of time resting on a type of tree called a birch tree, which normally has light-colored bark with dark spots on it.
在世界上的某些地方，胡椒蛾大部分时间都在桦树上休息，这种树通常有浅色的树皮，上面有黑色的斑点。
Something called lichen grew on the tree bark, which made it look even lighter.
树皮上会长地衣，使颜色看起来更淡。
That way, with their light-colored wings, they could blend in with the tree while they were resting and it would be harder for other animals, like birds, to find and eat them.
这样，其浅色的翅膀就可以在休息的时候与树融为一体，而其他动物，比如鸟类，就很难找到并吃掉它们了。
When animals blend in like that, it's called camouflage.
动物像这样混在其中，我们称之为伪装。
But even though almost all peppered moths had light-colored wings, there were a few with dark-colored wings with little light spots on them.
但是，尽管大部分斑点蛾的翅膀都是浅色的，但是也有一些翅膀是深色的，上面有小光点。
There weren't very many of them because it was really easy for birds to spot them against the light birch trees.
树上的蛾子并不多，因为鸟类很容易在白桦树下认出它们。
But then something happened to make the light trees become dark.
但是后来发生了一件事，使浅色的树变黑了。
About two hundred years ago, people started building factories, places where all sorts of things are made.
大约200年前，人们开始建造工厂，在那里制造各种各样的东西。
This was an exciting time because a lot of stuff was being made, and fast, too — everything from clothes to huge metal boats.
这是一个令人兴奋的时代，因为许多东西正被制造，而且速度也很快——从衣服到巨大的金属船。
We actually have a name for this special time: the Industrial Revolution.
事实上，这个特殊的时代有一个名字:工业革命。
But there was a big problem.
但有一个大问题。
The factories burned something called coal for energy to power their machines.
工厂燃烧煤作为能源来驱动机器。
They burned so much coal that the smoke made the air all dirty.
他们烧了太多的煤，以至于烟把空气都弄脏了。
That made those birch trees darker, too.
这也使得那些桦树变黑了。
It was like sprinkling little tiny bits of coal all over them.
这就像往他们身上撒一些小煤块。
And remember the lichen that grew on the trees?
还记得树上长出的地衣吗?
The dirt in the air made the lichen die, so they weren't there to brighten up the tree bark.
空气中的灰尘使地衣死亡，所以地衣不能再让树皮颜色变浅了。
The darker trees were a big problem for peppered moths.
深色的树木对有斑纹的蛾子来说是个大问题。
It used to be that the light-colored ones would blend in with the trees, but now they didn't, and they really stuck out.
以前浅色的会和树混在一起，但现在不是了，它们真的很突出。
It was super easy for birds to find them and eat them, and soon there weren't as many peppered moths as there used to be.
鸟类很容易找到它们并吃掉它们，很快就没有以前那么多有胡椒蛾了。
But those few moths with darker wings were totally fine — now that the trees were darker, it was easier for them to hide.
但那几只翅膀较黑的蛾子却安然无恙——现在树木更黑了，更容易躲藏。
Suddenly, more darker-winged moths were able to live long enough to have moth babies, which also had darker wings.
一时间，更黑翅膀的蛾子能够活得足够久，生下蛾子宝宝，而蛾子的翅膀也更黑。
And then those moth children grew up and had more moth children.
然后这些蛾子长大了，生了更多的后代。
So gradually, over many years, the moths with darker wings became way more common than the moths with lighter wings.
所以经过很多年，翅膀较暗的蛾子比翅膀颜色更淡的蛾子更常见。
Scientists call this process natural selection: when some living things have a trait that helps them survive, like the moths' darker wings, there end up being more babies that also have that trait.
科学家们把这一过程称为自然选择:当一些生物具有某种特征来帮助它们生存时，比如蛾子深色的翅膀，最终会有更多的后代具备这种特征。
That's how peppered moths changed from mostly having light wings to mostly having dark wings.
这就是为什么有斑纹的蛾子从长有浅色翅膀变成长有深色翅膀的原因。
But the story doesn't end there, Squeaks.
但故事并未就此结束，吱吱。
When people realized what the new factories were doing to the air, eventually they figured out new and better ways of making stuff without making the air as dirty.
当人们意识到新工厂对空气的影响时，他们最终想出了新的更好的方法来制造东西，而不是把空气弄脏。
Over time, the air got cleaner again, and guess what happened?
随着时间的推移，空气变得更干净了，猜猜发生了什么?
The bark on the birch trees got lighter again, and the lichen started to grow back.
桦树的树皮颜色又变淡了，地衣开始长出来。
Those moths with darker wings started to stick out again, and the moths with lighter wings had an easier time hiding from birds.
那些翅膀较暗的蛾子又开始变得明显起来，翅膀较淡的蛾子更容易躲避鸟类。
Natural selection happened all over again!
自然选择又发生了!
And today, the peppered moths with lighter wings are much more common than the ones with darker wings.
今天，翅膀较轻的胡椒蛾比翅膀较暗的胡椒蛾更常见。
That's where our story ends.
我们的故事到此结束。
But this was just one example of how one type of animal changed over time because there was something that helped some of them survive.
但这只是一种动物如何随着时间而改变的一个例子因为有某种东西帮助它们生存下来。
Natural selection happens with all types of living things, all the time.
自然选择每时每刻发生在所有种类的生物身上。
It just usually takes too long for us to notice it as it's happening.
通常我们需要很长时间才能注意到它的发生。
But it's how, a long long time ago, humans became very good at running.
但这就是很久很久以前，人类是如何变得非常擅长跑步的。
The people who were good at running had an easier time finding food and running away from animals trying to eat them,
擅长跑步的人更容易找到食物，并从试图吃他们的动物那里跑开，
so they had more babies, and pretty soon lots of humans could run.
所以他们有了更多的后代，很快很多人都擅长跑步。
Natural selection is also how rats became so good at smelling things —
自然选择也是老鼠嗅觉变得如此灵敏的原因——
they can smell animals that want to eat them from far away, so they have time to hide.
它们能够从很远的地方闻到想要吃掉它们的动物的气味，所以它们有时间躲起来。
There are examples of this type of change everywhere we look.
我们到处都可以看到这种变化的例子。
In a way, the story of the peppered moth is a lot like the story of how all life on earth has come to be.
在某种程度上，斑纹蛾的故事很像地球上所有生命是如何形成的故事。
Thanks for joining us!
感谢收看！
If you want to keep learning all sorts of amazing things about our incredible world and all the animals in it,
如果你想继续学习关于我们这个不可思议的世界和其中所有动物的各种神奇的事情，
hit the subscribe button, and be sure to check us out on the YouTube Kids app!
点击订阅按钮，一定要在YouTube Kids应用程序上查看我们!
We'll see you next time, here at the Fort!
我们下次见，就在这个堡垒!
