生命的奇迹（2013）

the mantis shrimp can still
借助复杂的眼睛
identify specific colours very accurately,
非常准确地识别特定的颜色
because of those sophisticated eyes.
皮皮虾的眼睛 完美地适应了它的需求
The mantis shrimp's eyes are beautifully tuned to their needs.
但和我们的眼睛大不相同
But they're very different from our eyes.
皮皮虾拥有数千个晶状体和复杂的色觉系统
With their thousands of lenses and their complex colour vision,
使它们以完全不同的视角观察世界
they have a completely different way of viewing the world.
然而力证表明 皮皮虾与人类的眼睛
And yet there's strong evidence that the mantis shrimp's eyes
有着共同的起源
and ours share a common origin.
因为在分子水平上
Because on a molecular level,
世界上所有生物的眼睛
every eye in the world
都有着相同的工作原理
works in the same way.
想要看到世界
In order to form an image of the world,
很明显 首先要能感光
then obviously the first thing you have to do is detect light,
我这里有一份样品
and I have a sample here
里面的分子有这功能
of the molecules that do that,
它们在我的眼睛中感光
that detect light in my eye.
具体来说
It's actually, specifically,
它们是存在于
the molecules that's in the black and white
视杆细胞中的分子
receptor cells in my eyes, the rods.
被称作视紫红质
It's called rhodopsin.
一旦被放置于光线下
And the moment I expose this to light,
就会立刻发生物理变化
you'll see an immediate physical change.
看吧
There you go.
看见了吗 变化非常迅速
Did you see that? It was very quick.
本来是粉红色
It came out very pink indeed,
之后立刻变成了黄色
and it immediately went yellow.
视紫红质分子在吸收光线时
This subtle shift in colour
自身形状发生变化
is caused by the rhodopsin molecule
引起了这种颜色的细微变化
changing shape as it absorbs the light.
而在人眼中
In my eyes, what happens is
这种变化会发出电♥信♥♥号♥♥
that change in structure triggers an electrical signal
并将其传输给大脑
which ultimately goes all the way to my brain,
由此形成外界的影像
which forms an image of the world.
这种化学反应
It is this chemical reaction
是地球上所有视觉的根源
that's responsible for all vision on the planet.
所有动物的眼中都聚集着这类分子
Closely related molecules lie at the heart of every animal eye.
这意味着它历来已久
That tells us that this must be a very ancient mechanism.
鸟 鱼 恐龙 鳄鱼 两栖类 蜥蜴和蛇类 灵长类 人类 鲸鱼 现今 1亿年前 2.5亿年前 5亿年前 10亿年前 20亿年前
要找到它的起源 我们必须找到
To find its origins, we must find a common ancestor
如今拥有视紫红质的生物的共同祖先
that links every organism that uses rhodopsin today.
可以肯定的是此共同祖先
We know that common ancestor must have lived
在物种分化前就已经存在了
before all animals' evolutionary lines diverged.
但它有可能存在于物种分化前的任何时期
But it may have lived at any time before then.
那个共同祖先究竟是什么
So what is that common ancestor?
于是我们只能诉诸于
Well, here's where we approach
先进的科学研究
the cutting edge of scientific research.
答案是 我们也不确定
The answer is that we don't know for sure,
但在这些小绿点中
but a clue might be found here,
我们能找到一些线索
in these little green blobs,
其实它们是一群
which are actually colonies of algae,
叫做团藻的海藻
algae called volvox.
人类和海藻几乎没有相似之处
We have very little in common with algae.
早在十亿年前
We've been separated
人类就与它们向不同方向进化
in evolutionary terms for over a billion years.
但我们的确有一个惊人的共同点
But we do share one surprising similarity.
团藻
团藻属
团藻利用感光细胞
These volvox have light-sensitive cells
控制自身运动
that control their movement.
这些细胞中的活性成分
And the active ingredient of those cells
与人眼中的视紫红质如此相似
is a form of rhodopsin so similar to our own
以至于两者被认为拥有共同起源
that it's thought they may share a common origin.
这有什么含义呢
What does that mean?
是否意味着人类与海藻有共同的祖先
Does it mean that we share a common ancestor with the algae,
而在这个共同祖先的体内
and in that common ancestor,
能够找到视觉的起源
the seeds of vision can be found?
绿藻
为了找到
To find a source
是什么将这种感光能力
that may have passed this ability to detect light
同时遗传给人类和藻类
to both us and the algae,
我们必须再往回追溯
we need to go much further back down the evolutionary tree.
蓝细菌
一直到蓝细菌
To organisms like cyanobacteria.
它们是地球上首批开始进化的生物
They were among the first living things to evolve on the planet,
最初的视紫红质可能就形成于
and it's thought that the original rhodopsins may have developed
这些古老的光合细胞内
in these ancient photosynthetic cells.
因此人类视觉的基础
So the origin of my ability to see
可能早在十亿年前
may have been well over a billion years ago,
在蓝细菌这样的
in an organism
简单生物体内奠定了
as seemingly simple as a cyanobacteria.
视觉的基本化学原理
The basic chemistry of vision
可能由来已久
may have been established for a long time,
但距离眼睛能进行完整的成像
but it's a long way from that chemical reaction
还有很长一段时间
to a fully functioning eye that can create an image of the world.
眼睛是一种异常复杂的结构
The eye is a tremendously complex piece of machinery,
由许多相互独♥立♥的部件组成
built from lots of interdependent parts,
似乎很难想象
and it seems very difficult to imagine
它们到底如何逐步进化成如今的模样
how that could have evolved in a series of small steps,
但事实上 我们对这个过程了如指掌
but actually, we understand that process very well indeed.
美国
南加州
大学
我会制♥作♥一只眼睛来示范
I can show you, by building an eye.
制♥作♥眼睛的第一步
The first step in building an eye
是获取感光原料
would need to take some kind of light-sensitive pigment,
比如视紫红质 并将固定在一层膜上
rhodopsin, for example, and build it on to a membrane.
假设这就是那层膜
So imagine this is such a membrane,
上面附着感光细胞
with the pigment cells attached,
它就能立刻区分
then immediately you have something that can detect
光与暗
the difference between dark and light.
此装置的优点在于
Now, the advantage of this arrangement
它对光线非常敏感
is that it's very sensitive to light.
视网膜前面没有遮挡光线的物体
There's no paraphernalia in front of the retina to block light,
但也有缺点 可以看到
but the disadvantage, as you can see,
它完全无法成像
is that there is no image formed at all.
只能用来区分光和暗
It just allows you to tell the difference between light and dark.
但想大大改进此装置
But you can improve that a lot
只需加上一个光圈
by adding an aperture,
也就是视网膜前面的小孔
a small hole in front of the retina,
这是一个可调整的光圈
so this is a movable aperture,
就像照相机里的光圈
just like the sort of thing you've got in your camera.
现在图像更加清晰了
And now, we see that the image gets sharper.
要把它变得更清楚
But the problem is that in order to make it sharper,
必须缩小光圈
we have to narrow down the aperture,
这意味着进入眼睛的光线越来越少
and that means that you get less and less light,
眼睛也变得不那么敏感
so this eye becomes less and less sensitive.
所以大自然又改进了眼睛的结构
So there's one more improvement that nature made,
就是把这个小孔
which is to replace the pinhole,
即简易光圈
the simple aperture...
替换成晶状体
with a lens.
瞧
Look at that.
非常清晰的成像
A beautifully sharp image.
眼睛成像的关键就在于晶状体
The lens is the crowning glory of the evolution of the eye.
光线经其折射到达视网膜
By bending light onto the retina,
同时让瞳孔张开
it allows the aperture to be opened,
允许更多光线进入
letting more light into the eye,
明亮而清晰的图像由此形成
and a bright, detailed image is formed.
人眼被称为摄像机眼
Our eyes are called camera eyes,
因为和照相机一样
because, like a camera,
人眼只有一块透镜
they consist of a single lens
将光线折射到感光器上
that bends the light onto the photoreceptor
形成高质量的图像
to create a high-quality image of the world.
但此结构存在缺点
But that has a potential drawback,
要理解这么多的信息