Using the example of the pronghorn and lion, explain the concept of a relict behavior.
请以叉角羚和狮子为例解释说明孑遗行为的概念。
Read a passage about Relict Behaviors from a biology textbook.
请阅读这篇选自生物课本的关于孑遗行为的文章。
You will have 50 seconds to read the passage. Begin reading now.
你将有50秒的时间阅读文章，现在开始计时。
Now listen to part of a lecture in a biology class.
请听生物学课上的部分内容。

Ok, uh, so a good example of this, found right there in North America,
关于这个话题的一个很好的例子，正好就是在北美洲发现的，
is something an animal called the American Pronghorn does.
有一种叫美洲叉角羚的动物就是如此。
Pronghorns, as you may know, are a kind of deer-like animal,
你们可能知道，叉角羚是一种长得很像鹿的动物，
they live out in the open grassy plains, somewhat in the middle of North America, and they are super fast.
它们生活在开阔的草原上，主要集中在北美洲中部，跑起来超级快。
Pronghorns are, in fact, noted for being the fastest animal in the western hemisphere.
事实上，叉角羚被认为是西半球跑得最快的动物。
Once a Pronghorn starts running, zoom!
一旦叉角羚开始跑了起来，“噌”地一下就不见了！
None of its present predators, like the bobcat or the coyote, can even hope to catch up with it.
在它现在的天敌中，比如山猫或者狼，没有一个有望追得上它的。
It's off in a flash! Ok, so why then do Pronghorns run so fast? That's the question.
它跑起来就像一道闪电，十分迅速！那么，叉角羚为什么要跑得这么快呢？这才是我们今天要讨论的问题。
Well, it turns out that quite a long time ago,
原来，在很久以前，我说的可是数万年前，
I'm talking tens of thousands of years, things on the grassy plains used to be very different for the Pronghorns.
对叉角羚来说那时候草原上的情况和现在非常不同。
Because back then, lions used to live on the plains, chasing and preying upon the Pronghorns,
因为那个时候，这片草原上还住着狮子，它们追赶捕食着叉角羚，
and lions, of course, are a very swift-moving mammal,
而狮子，毫无疑问是一种行动非常迅速的哺乳动物，
much faster than the bobcat or coyote or other predators you'd find on the plains today.
比山猫和狼或者如今能在草原上看见的其他食肉动物都要快得多。
But, now, however, lions are all extinct in North America, there're no longer a predator of the Pronghorn.
然而，现在北美洲的狮子都已经灭绝了，再也没有专门捕食叉角羚的食肉动物了。
Tens of thousands of years ago, though, the lions were there chasing the Pronghorns.
可是数万年前，狮子们还在不断追赶着叉角羚。
So back then, the Pronghorn's speed was critical to its survival.
所以那个时候，叉角羚的速度决定着它的存亡。