生命的奇迹（2013）

and for that to happen,
只需使正负极间形成电势差
you need an imbalance between positive and negative charges.
如今 自然界中的物体通常呈电中性
Now, usually in nature, things are electrically neutral,
正负极之间几乎不存在电势差
the positive and negative charges exactly balance out,
但也有自然现象
but there are natural phenomena in which there is a separation
会使正负电荷分离
of electric charge.
例如 雷雨
A thunderstorm, for example.
一旦形成雷雨云
As thunder clouds build,
它们之间上升的气流使正负电荷分离
updraughts within them separate charge.
较轻的冰水晶体带正电
The lighter ice and water crystals become positively charged
并向上运动
and are carried upwards,
而较重的晶体
while the heavier,
带负电荷向下沉至云层底部
negatively charged crystals sink to the bottom.
这样一来 地面与云层间
This can create a potential difference,
1亿
伏特
便形成了高达1亿伏特的
a voltage between the cloud and the ground of as much as
电势差
100 million volts.
自然界憎恶梯度的出现
Now, nature abhors a gradient.
它不喜欢这种失衡现象
It doesn't like an imbalance,
大自然会通过产生电流来平衡电势差
and it tries to correct it by having an electric current flow.
雷雨天气中的闪电便因此而生
In the case of a thunderstorm, that's a bolt of lightning.
营业中
这个过程同样支配草履虫的行为
And it's the same process that governs the paramecium's behaviour,
只不过是微观版的
but on a tiny scale.
几乎所有的细胞都是这样
In common with virtually all other cells,
当然也包括动物细胞
and certainly all animal cells,
草履虫的细胞膜表面
the paramecium maintains a potential difference
始终存在电势差
across its cell membrane.
其实现方式同雷雨一样 造成正负电荷分离
It does that in common with a thunderstorm by charge separation.
通过控制细胞膜内外的
By manipulating the number of position ions
正离子数量
inside and outside its membrane,
草履虫产生约40毫伏的
the paramecium creates a potential difference of
电势差
just 40 millivolts.
当草履虫静止
So when a paramecium is just sat there,
不碰撞任何物体
not bumping into anything,
仅在液体中漂浮时 它就像一个小电池
floating in this liquid, then it's like a little battery.
始终保持细胞膜内外
It's maintaining the potential difference
存在电势差
across its cell membrane,
草履虫运用这种方式感知外界环境
and it can use that to sense its surroundings.
当它撞到某物时 细胞膜变形
When it bumps into something, its cell membrane deforms,
离子通道打开 正离子通过这些通道
opening channels that allow positive ions to flood back
内流至细胞内
across the membranes.
电势差的下降
As the potential difference falls,
脉冲:很短的时间内变一次电压的过程
引起了电脉冲 从而触发纤毛
it sets off an electrical pulse that triggers the cilia
开始朝相反方向摆动
to start beating in the opposite direction.
电脉冲通过动作电位
That electrical pulse spreads round the whole cell in a wave
在整个细胞表面扩散
called an action potential.
草履虫便全身而退
And the paramecium reverses out of trouble.
这种准确控制细胞膜内外
This ability to precisely control
电流流动的能力
flows of electric charge across a membrane
并非草履虫独有
is not unique to the paramecium.
实际上这是所有动物感官的核心
It actually lies at the heart of all animal senses.
事实上 每当我感觉到某样东西
In fact, every time I sense anything in the world,
无论通过眼睛 耳朵 还是手指
with my eyes, with my ears, with my fingers,
感觉传到大脑前的某一时刻
at some point between that sensation and my brain,
会进行和这个相同的生理活动
something very similar to that will happen.
虽然所有感知都运用相同的生物电机理
Although the same electrical mechanism underpins all sensing,
但每种动物的感知能力却自成体系
every animal has a different suite of sensory capabilities
与它们的生存环境完美契合
that is beautifully adapted to the environment it lives in.
这是大布莱克河
This is the Big Black River,
磅礴的密西西比河支流
a tributary of the mighty Mississippi
位于美国的南方腹地
in America's deep south.
在这片阴暗混浊的水域里
And these dark and murky waters
生存着一种凶猛的肉食动物
are home to a ferocious predator.
扁头鲶
虽然在水下
Even though it's impossible to see
能见度只有几厘米
more than a couple of inches through the water,
这种肉食动物却有办法追踪并捕食猎物
this predator has found a way to track down and catch its prey
而且效率惊人
with terrifying efficiency.
为了抓到它
To help me catch one,
我向野生生物学家唐·杰克森求助
I've enlisted the support of wildlife biologist Don Jackson.
就是它
That's it.
我得制♥服♥它
Wrestle it a bit. I'll wrestle it now.
把它弄到这边来 -是吗
He's going over right here. - Is he?
搞定了
There you go.
它会咬人
He can bite. Argh!
让你瞧瞧这家伙的嘴
I'll show you the mouth of this thing.
等会儿
Hang on...
猎物眼中 它就是这个样子
So you can see what the prey sees when he comes.
只要嘴里装得下 它都来者不拒
Anything that'll fit in that mouth, he'll grab it!
你用两手从下面把它牢牢托住
You can hold him if you just want to put your hand
就能抱住它了
all the way under him.
全部托住 全部
Come all the way. All the way.
离你近一点 对
Hold him up close to you. Yeah.
感觉怎么样 -我抓住它了
How about that? - I've got him. Yeah.
它是这条河中的顶级掠食者
This is the top predator in this river.
它是什么来着
This is a, what?
一条约11千克重的扁头鲶
A 25-pound flathead catfish.
看见它头部的突出物了吗
You see those protrusions from his head?
那些是触须
Those are barbels.
能在河床的泥沙中感觉到振动
They sense a vibration in the mud, on the river bed,
但这种鲶鱼最不可思议的地方在于
but the most interesting thing about the catfish
某种程度上 它就是一条大舌头
is that she really is, in some ways, one big tongue.
它的体表全都覆盖着味觉传感器
There are taste sensors covering every part of her body,
味蕾
700/平方厘米
它能够通过感知动物的化学味道
and she can build up a 3D picture of the river
构建起河流的立体画面
by detecting the chemical scents of animals.
所以它的眼睛没多大作用
So, her eyes are not much use.
正如你看到的 河水十分泥泞
As you can see, this river's extremely muddy,
味觉因此承担起了
but it's the sense of taste that does the job
感知周围环境的职责
of building up a picture of the world,
这就是它捕食的方法 而且它其重无比
and that's how he hunts, and he weighs a ton.
我能感觉到它的牙齿
I can feel those teeth.
我要松手了
I'm going to let go.
好吧 伙计 去吧
All right, you. Go on.
鲶鱼的感官世界非同寻常
The sensory world of the catfish is a remarkable one.
它眼中的世界 由水中
Its map of its universe is built from the thousands of chemicals
成千上万种化学物质构成
it can detect in the water.
无数味道和香味
A swirling mix of tastes and concentrations,
涡旋着混合在一起
flavours and gradients.
这是一个我们难以想象的世界
It's a world we can hardly imagine.
从中我们能得到一个有趣又富含哲理的结论
There's an interesting almost philosophical point here
我们习惯于认为人类是从客观的角度
because it's easy to imagine that we humans perceive the world
来观察世界
in some kind of objective way,
但事实并非如此
but that's not the case at all.
想想鲶鱼吧
Think about the catfish.
鲶鱼眼中的世界
The catfish sees the world
是河流中无数种化学物质的集♥合♥
as a kind of swarm of chemicals in the river,
或是河床上的振动
or vibrations on the river bed,
而我们眼中的世界 是森林上反射的光
whereas we see the world as reflected light off the forest,
我还能听到某处灌木丛下
and I can hear the sounds of animals out there
动物的叫声
somewhere in the undergrowth.
鲶鱼看待世界的角度则完全不同
The catfish sees the world completely differently.
你所处的环境决定了
So the way you perceive the world is determined
你观察世界的方式
by your environment,
每种动物观察世界的方式都独一无二
and no two animals see the world in the same way.
和所有动物一样
Like every animal,
人类进化出了适应生存环境
we have evolved the senses that enable us to live
的感官
in our environment.
除了让我们适应当下
But as well as equipping us for the present,
感官也能帮助我们了解过去
those senses can also tell us about our past.