生命的进化（1979）

until you put up a mercury vapour lamp in the tropics.
几分钟以后，你可以看到很多各种各样的动物
Here, within a few minutes, you've got all sorts of creatures.
小飞蛾、螅蟀、大甲虫、螳螂、
Small moths, crickets, huge beetles, mantises,
大飞蛾，几乎所有的昆虫种类
big moths, insects of all kinds.
在3亿年前，昆虫最早出现在天空
The insects first took to the air about 300 million years ago.
它们独自生活了大约一亿年
They had it to themselves for about 100 million years,
直到爬行动物来临
at least until the arrival of the reptiles.
我们不知道是否有晚上飞行， 捕食昆虫的爬行动物
Whether there were any night-flying, insect-hunting reptiles, we don't know,
但是看起来不可能，因为爬行动物是冷血动物
but it seems unlikely because reptiles, being cold-blooded,
它们平常在白天活动
are usually active during the day.
在一亿五千万年前，鸟类出现了
And then about 150 million years ago, the birds developed.
但是没有理由去猜测
But there's no reason to suppose
在过去晚上飞行的鸟多于现在，
there were any more night-flying birds in the past
那是很少数
than there are today, and that's precious few.
因此大量的昆虫
So this great feast of insects
等来的是可以在晚上自♥由♥飞行的动物
awaited any creature that could master the tricky technique of flying at night.
一种哺乳动物，
And one group of the mammals did.
蝙蝠
The bats.
大多数都是猎食飞行昆虫的猎手
The majority of them are hunters of flying insects,
像飞蛾、蚊子甚至于甲虫
such as moths, mosquitoes or even beetles.
当蝙蝠倒挂的时候， 抓住昆虫，并在栖息所吃掉它们
Caught on the wing and eaten at the roost as the bats hang upside down.
在很久以前蝙蝠就能够飞行了
Bats began to fly a very long time ago.
毫无疑问， 这块骨头化石是5千万年前的蝙蝠
These fossil bones of what is undoubtedly a bat are about 50 million years old.
蝙蝠的骨骼与树鼠非常相似
The bat skeleton is very similar to the tree shrew's.
从上面看，现在再从侧面看
Seen here from above, and now side on.
但是它是怎样变成会飞的动物的呢？
But how did this flying variation arise?
也许最早的食蚁动物在树上寻找食物
It may be that the early insect-eaters sought their food up in the branches of trees,
就像现在的树鼠一样
as indeed some kinds of tree shrews do today.
它们跳起来努力去抓那些在空中飞行的昆虫
And as they leapt about trying to snatch flying insects from the air,
有一些在臂和身体侧面之间长出了皮翼
some may have developed flaps of skin between their arms and the sides of their body
以至于它们能滑翔，像现在的松鼠一样
so that they could glide, as the living flying squirrels can today.
然后它们用指支撑着翼，并增强臂部肌肉
They then supported those flaps with their fingers and strengthened the arm muscles
直到最后它们能用新长出来的翼进行滑翔
until, eventually, they were able to flap their newly developed wings
并飞出去寻找它们喜欢的昆虫， 最终就变成了蝙蝠
and fly in search of their insect prey, and so became bats.
但是以昆虫为生有很大的缺点
But living on insects has one great disadvantage.
在世界的大多数地方，昆虫会在冬季消失
In many parts of the world insects disappear almost totally during the winter.
在那时，这些食虫动物又怎么办呢？
What does an insect-eater do then?
它们会找一个隐蔽的地方冬眠
It hibernates in any sheltered place it can find
并且那个地方的温度能保持一定的水平 而且要略高于其他地方的温度
where the temperature might remain a few degrees higher than elsewhere,
像旧的加拿大矿厂里面
as it is inside this old Canadian mine.
有些小的块，像冰冷的石头一样， 实际上是蝙蝠在里面
These tiny lumps, as cold as stone, are living bats.
在夏季，它们贪婪地吃东西以贮存更多的脂肪
They fed voraciously during the summer, building up reserves of fat,
但是现在在它们的身体里发生一个重要的变化
but now a profound change has taken place in their bodies.
它们身体的热量在散失， 身体的反应在变慢
Their heat has seeped away, and their body processes have slowed down
但是没有完全停止
to almost, but not quite, a complete halt.
它们必须保持身体的化学反应慢慢进行
They must keep their body chemistry ticking over
仅仅产生足够的热量 防止身体被冻僵
just enough to generate sufficient heat to prevent them from freezing solid,
要不然就不能再存活
for that they can't survive.
并不是所有的都能成功
Not all of them are successful.
有时候，一些单独的蝙蝠不能躲避寒冷
Sometimes an individual cannot stave off the chill,
掉下来埋葬在冰雪中
falls and is entombed in the ice.
你也许会想它们可以挤在一起来保持温暖
You might think they huddle together to keep warm.
但是，精确的测量显示它们在一起还是冰冷
But careful measurements have shown those in groups get just as cold
像它们单独倒挂着一样
as those hanging by themselves.
也许在一起可以保护它们远离其它的危脸
It may be that grouping protects them from another hazard,
在呼吸中湿气的损失
the loss of moisture during breathing.
看起来要比一群要少一些
That does seem to be less for those in clusters.
其他动物也在矿厂中寻求避难所
Other creatures also take refuge in the mine,
尤其是夏季作为蝙蝠食物的蚊子
the very ones which in summer are food for the bats: moths.
猎手和猎物躲避在一起躲避致命的杀手，寒冷
Both hunters and hunted shelter together from that overwhelming killer, cold.
在世界的其他地方，如新墨西哥
In other parts of the world, as here in New Mexico,
为了解决缺少食物的问题，蝙蝠要迁移
bats solve the problem of lack of insect food by migrating.
到了冬季，它们向南飞行1000公里
From this cave they will fly south some 1,000km for the winter.
它们不得不找到足够的食物
They have to, to find enough food,
由于它们以十万计的数目
for their populations are measured in millions,
需要很多昆虫
and tons of insects are needed.
像这样的洞穴有着数量密集的哺乳动物
Caves like these contain the densest populations of mammals
在地球上任何一个地方部可以找到
to be found anywhere on earth.
那些蝙蝠是怎样用相同的速度飞的？
How is it that all those bats flying at such a speed
在黑暗中怎么能找到路呢？
can find their way around in the dark?
答案是回声定位法
The answer is echolocation.
尽管我能听到微弱的鸣声
Although I can only hear just the faintest twitter,
事实上，每一个蝙蝠都能 发出或多或少的连续的长鸣声
in fact each bat is emitting a more or less continuous stream
一种在我们听觉范围以外的高频率声音
of high-frequency sound beyond the range of my ears.
但是，我可以把这种声音用机器 转换成我能听见的声音，就像这样
But I can translate those into sounds that I can hear using a machine like this.
蝙蝠检测器，听
A bat detector. Listen.
（鸣声）
(TWITTERING )
这个系统是以那些 高声调的超声波为基础的
The system is based on those high-pitched ultrasounds,
像现在那些制♥造♥噪音的人一样
like those produced today by shrews
早期的食虫动物可能也是这样的
and which the early insect-eaters may have used as well.
蝙蝠发展了那种能力
The bats have developed that ability
使之成为一种叫声纳的高精技术
into a highly sophisticated technique called sonar.
每一个蝙蝠发出一连串短的尖叫声
Every bat sends out a stream of short squeaks,
每秒可达20到30次，或者更多
which can be as many as 20 or 30 a second, or even more.
从回声中可以测量出到物体的距离
From the echoes it can gauge its distance from an object,
是洞穴的墙壁还是空气中昆虫
whether it's a cave wall or an insect in the air.
马蹄蝙蝠的声波是从鼻孔里产生的
The horseshoe bat produces such ultrasounds from its nostrils,
鼻子的构造使其像扩音器
and that construction around the nose serves as a megaphone,
把声音集成一束
focusing the sound into a beam.
研究这些声音最简单的方法是 用特殊的麦克风把它们收集起来
The easiest way to study these signals is to pick them up with a special microphone
然后把它们转换到示波器上， 用虚拟的方式分♥析♥
and relay them to an oscilloscope so that they can be analysed in a visual form.
示波器告诉我们蝙蝠发出了声音
The oscilloscope tells us that the bat is producing sounds,
尽管它不在我们的听力范围以内
though they are beyond the range of our hearing.
但是只要用合适的仪器，我们可以
But with the right equipment we can translate those ultrasounds
把这些超声波转换成我们能听见的声音
into sounds that we can hear.
（高音调脉冲）
(HIGH-PITCHED PULSE)
用示波器我们可以听和看
With the oscilloscope as well, we can both see and hear
那些蝙蝠制♥造♥的声音
the variations that the bat can make.
（更快的高音调脉冲）
(FASTER HIGH-PITCHED PULSE)
（脉冲慢下来）
(SLOWER PULSE)
（脉冲变快）
(FASTER PULSE)
另一种识别蝙蝠信♥号♥♥的方式
Another way to analyse the bat's signals
用一种特殊的录音机使它慢下来
is to slow them down using a special tape recorder.
这是被放慢32倍的马蹄蝙蝠的声音
These are the horseshoe bat's ultrasounds slowed down 32 times.
（长长的音符）
(LONG WHISTLING NOTES)
另一个种类的声音也被放慢
This is a different species also slowed down.
它从嘴里发出这种超声波
And it's emitting the ultrasounds through its mouth.
从猎物那反射回来的回声信♥号♥♥
With these echolocating signals bouncing back off the prey,
蝙蝠可以非常准确地找到位置， 当它越靠近就会增加音频发出量
bats can home in very accurately, raising the rate of output as they approach.
（蝙蝠的吱吱声）
(BAT CHIRRUPPING)
声音和行动都被放慢15倍
Both sound and action are slowed down 16 times.
作为诱饵的虫子被准确地用声纳找到
The bait, a mealworm, is located precisely by sonar,
蝙蝠首先用翅膀的隔膜抓到它
and the bat, a pipistrelle, catches it first with its wing membrane,
然后把它弹出并穿过尾巴的膜
then flicks it across to its tail membrane,
此时虫子到了头部，所以虫子被送到了嘴里
which is then brought up to its head so the mealworm is passed to the mouth.
尾巴的膜还在头顶处
The tail membrane is still over the head.
现在一切恢复原状， 蝙蝠继续去捕捉其他飞着的虫子
Now it's pulled back, and the bat continues to eats its prey in flight.
自从蝙蝠进化成以丰富的昆虫为食
Since bats evolved to take advantage of the rich insect larder,
昆虫自身也在不停地发展，看！
the insects themselves have developed their own countermeasures. Watch.
草蛄蛉逃身的技巧
The lacewing's escape technique
它收起翅膀，从蝙蝠的必经路上掉下来
is to close its wings and fall out of the path of the bat.
在草蛄蛉的翅膀上有很小的耳朵
Lacewings have tiny ears on their wings.
在捕食者和被捕食者的斗争之中，昆虫听到了
So in this conflict between predator and prey, the insect has tuned in
昆虫听到了蝙蝠到来的声音 因此及时釆取了避开它的方法
to be able to hear the bat coming, and therefore take avoiding action.
有些飞蛾，像虎蛾， 甚至有一套详尽的防御方法
Some moths, including tiger moths, have an even more elaborate defence.
它不但能听到蝙蝠的来临声， 还能俯冲或盘旋地飞行
Not only can they hear bats coming and then dive or spiral away,
最后，作为一种手段，它能发出自己的声音
but, as a last resort, they can emit their own sounds.
首先，我们能听到恐吓蝙蝠的声音
First we will see and hear the sound of the threatening bat,
作为飞蛾的反击
and then the reaction of the moth.
（破裂声）
(CRACKLING)
飞蛾要么混杂了蝙蝠的声音