听力文本

The missing link had to be what Charles Darwin called a transitional form.
进化缺环必须是达尔文所谓的“过渡型物种”
These lie at the very heart of his Theory of Evolution because they show how one animal can mutate into another.
它们是进化论的核心，因为它们表明一种动物能够进化成另一种动物
Transitions occur in evolution when there is a dramatic environmental change.
进化史上的演变通常发生在环境剧变时期
Creatures that cannot adapt to the new environment die out.
无法适应新环境的物种灭绝了
but chance mutations often turn out to be the key to survival.
可是偶然的突变却往往成为生存的关键

There is an explosion of bizarre forms as a host of mutants experiment with living in the new environment.
新环境中有如此多的生存突变试验，势必造成了各种奇怪物种的大爆发
These freaks of nature will die out quickly and just some will become transitional forms,
这些大自然的畸形儿很快便消亡了，只有一部分成为了过渡型物种
creatures that are half one animal and half another which bridge the old way of living and the new.
它们一半是一只动物，一半是另一只动物，在新旧生存方式之间架起了桥梁
Transitional forms are the most crucial fossils in all evolution.
过渡型物种是所有进化中最关键的化石物证
They're important to the zoologist, to the palaeontologist because they,
它们对动物学家和古生物学家来说非常重要
they show you what the process actually was.
因为它们表现了进化的过程，
I think they're very important to the public as,
我认为它们对大家来说都很重要
as being direct evidence that there was a process of change that you can document.
因为它们是你用以证明演化过程的直接证据

词汇解析

1.mutate into 进化成
In very rare instances, the virus in the vaccine can mutate into a form that can paralyse.
在极少的情况下，疫苗中的病毒可能变异成一种可导致瘫痪的类型。

2.adapt to 适应
When you go to a new country, you must adapt yourself to new manners and customs.
当你新到一个国家时，你必须使自己适应新的风俗习惯。

3.turn out to be 成为
Unfortunately they do not turn out to be more creative; they only feel that way.
不幸的是，他们最终并没有更具创造力；那只是他们的感觉而已。

视频及简介

19世纪，英国生物学家赫胥黎在研究了尼安德特人的头骨以后，认为是一个具有猿脸的头骨，但决不是人与猿之间的中间缺环。这就告诉我们，人与猿之间的亲缘关系，似乎还应该有一环。1891年发现直立猿人（爪哇猿人）的骨胳，证明这个缺环确实是存在的。可是，日本的人类学家认为爪哇猿人尚不是真正的中间缺环。那么，在猿与人之间到底应该是什么样的一环呢？在埃塞俄比亚发现的早期人科动物化石，很可能是过渡物种。这一发现，弥补了原始人类进化中的一个“缺环”。