生命的奇迹（2013）

人类拥有和草履虫一样的触觉
Now we have a sense of touch like the paramecium,
也像鲶鱼一样具备化学感官
and we have the chemical senses,
包括味觉和嗅觉
taste and smell, like the catfish,
但对我们而言
but for us,
听觉和视觉才是最主要的
the dominant senses are hearing and sight,
要了解它们
and to understand them,
我们必须先了解它们的进化史
we first have to understand their evolutionary history.
所以我来到了加利福尼亚的莫哈韦沙漠
And that's why I'm in the Mojave Desert in California,
追踪一种能揭示
to track down an animal that can tell us something
人类感官起源的动物
about the origins of our own senses.
在黑暗中最易发现这种生物
The creature I'm looking for is easiest to find in the dark,
借助紫外线手电
using ultra-violet light.
天呐 你看见了吗
Man! Did you see that?
莫哈维沙漠蝎
你们看 太诡异了
Look at that. Absolutely bizarre.
它浑身呈荧光绿色
It's glowing absolutely bright green.
没人知道这是一种怎样的进化优势
Nobody has any idea what evolutionary advantage that confers.
虽然现在它们生活在地球上
Although they now live in some of the driest,
最干旱恶劣的环境中
most hostile environments on Earth,
像是这片沙漠
like here in the desert,
但约3.8亿年前 第一只蝎子爬上岸前
scorpions evolved as aquatic predators
它们却是水生掠食者
before emerging onto the land about 380 million years ago.
它们已适应极端高温的环境
They've adapted to be able to survive the extreme heat,
而且可以一整年不吃不喝
and can go for over a year without food or water.
虽然名声骇人
Despite their fearsome reputation,
但98%蝎类的毒刺
98% of scorpion species
只不过和蜜蜂的差不多
have a sting that is no worse than a bee's.
从进化角度来看
Perhaps the most fascinating thing about scorpions
蝎子最吸引人的地方
from an evolutionary perspective
也许是它捕猎的方式
is the way that they catch their prey.
你能看到它把腿全部张开
You see that he spreads his legs out
铺散在沙面上
on the surface of the sand.
因为它利用腿来探测振动
And that's because he uses his legs to detect vibrations.
蝎子捕食昆虫 例如这只甲虫
Scorpions hunt insects like this beetle.
甲虫在黑暗中难以看见
It's almost impossible to see them in the dark,
所以蝎子进化出其他方法来找到它们
so the scorpion has evolved another way to track them down,
通过触觉
by adapting its sense of touch.
昆虫四肢着地在沙面上爬行
As the insect's feet move across the sand,
会在地面引发微弱的振动波
they set off tiny waves of vibration through the ground.
只要在蝎子所处范围内
If just a single grain of sand is disturbed
有一粒沙子产生了振动
within range of the scorpion,
它都能通过腿部尖端立刻感知
it will sense it through the tips of its legs.
它们在爬行中
They can detect vibrations
可以感测到
that are around the size of a single atom
原子的震动
as they sweep past.
通过计算振动波
By measuring the time delay,
到达各腿间的时间差
between the waves arriving at each of its feet,
蝎子能准确定位猎物方向
the scorpion can calculate the precise direction
及两者间距离
and distance to its prey.
这种探测振动
And that ability to detect vibrations
并利用它构筑周围环境的能力
and use them to build up a picture of our surroundings
是人类和蝎子共有的
is something that we share with scorpions.
蝎子利用触觉
While the scorpion has adapted its sense of touch
来感知地面的振动
to detect vibrations in the ground,
而人类则利用相似的原理
we use a very similar system
来感知空气中的微弱振动
to detect the tiny vibrations in air
我们称之为声音
that we call sound.
和蝎子一样
And like the scorpions,
我们的听觉系统也极其敏锐
ours is a remarkably sensitive system.
我们听觉的范围很大
Our ears can hear sounds over a huge range.
鳄鱼交♥配♥的叫声
20赫兹
我们能听到位于声谱最低端的
We can detect sound waves of very low frequency
超低频声波
at the bass end of the spectrum.
青蛙合唱
3500赫兹
但我们也能听见尖锐的声音
But we can also hear much higher-pitched sounds,
频率达到前者的几百
sounds with frequencies hundreds
破晓鸟鸣
4000赫兹
乃至几千倍
or even a thousand times greater.
我们还能感知到声音强度的巨变
And we can detect huge changes in sound intensity...
蚊子
40分贝
从昆虫振翅
From the delicate buzzing
发出的细微嗡嗡声
created by an insect's flapping wings...
汽艇
120分贝
到比前者响亮1亿倍的
to the roar of an engine,
引擎轰鸣声
which can be 100 million times louder.
人类听觉的发展史
The story of how we developed our ability to hear
是物种进化的最好例证之一
is one of the great examples of evolution in action.
因为第一批
Because the first animals
从水中爬上岸的动物
to crawl out of the water onto the land
在新环境中
would have had great difficulty hearing anything
必定难以听到声音
in their new environment.
这里是大沼泽地
These are the Everglades.
一望无际的沼泽和湿地
A vast area of swamps and wetlands
覆盖佛罗里达的南端
that has covered the southern tip
长达4000余年
of Florida for over 4,000 years.
通过观察这里的动物
Through the creatures we find here,
美洲短吻鳄
短吻鳄属
例如美洲短吻鳄 鳄科的一员
like the American alligator, a member of the crocodile family,
我们可以描述人类听觉的发展史
we can trace the story of how our hearing developed
从登上陆地的那一刻开始
as we emerged onto the land.
最先拥有听觉的 是水下的鱼类
And it starts below the water, with the fish.
如果你是一条鱼
If you're a fish, then
那么你的听觉并无障碍
hearing isn't a problem.
你在水里生活 由水构成
You live in water and you're made of water,
所以声音能够轻易的从外界传播
so sound has no problem at all travelling from the outside
到身体中
to the inside,
但当生命从海洋发展到陆地上时
but when life emerged from the oceans onto the land,
听觉就面临着难题
then hearing became a big problem.
声音不能从空气中清晰地传入水中
See, sound doesn't travel well from air into water.
如果我现在发出声音
If I make a noise now...
99.9%以上的声音
over 99.9% of the sound
都会被水面反射回来
is reflected back off the surface of the water.
因为存在这样的反射
It's because of that reflection
水面上的声音很难在水下听到
that underwater you can hear very little from above the surface.
我们的耳朵也面临同样的问题
And it's exactly the same problem our ears face,
因为它们也充满液体
because they too are filled with fluid.
如果进化过程中没有诞生
So, if evolution hadn't found
一种巧妙的解决方法
an ingenious solution to the problem
让声音从空气传入液体中
of getting sound from air into water,
那我现在就什么都听不见了
then I wouldn't be able to hear anything at all.
这一解决方法
And that solution
得益于人体内一些最精妙
relies on some of the most delicate moving parts
的活动结构
in the human body.
是不是掉了
Have I just dropped them?
等一下
Hang on a second.
又掉了
Oh, I've done it again!
该死 真笨
Bloody hell! Idiot!
不见了
Just flipped out!
这是人体内最小的三根骨骼
These are the smallest three bones in the human body,
叫做锤骨 砧骨和镫骨
called the malleus, the incus and the stapes,
它们位于鼓膜
and they sit between the eardrum
和内耳道之间
and the entrance to your inner ear,
直通流体所在的位置
to the place where the fluid sits.
这些骨头通过两个机制
The bones help to channel sound into the ear
将声音导入耳内
through two mechanisms.
首先 它们作为杠杆
First, they act as a series of levers,
放大了鼓膜震动的幅度
magnifying the movement of the eardrum.
其次 因为鼓膜的表面♥积♥
And second, because the surface area of the eardrum
鼓膜
是镫骨的17倍
is 17 times greater than the footprint of the stapes,
镫骨
震动会以更大的力量