The evolution of the human eye - Joshua Harvey

翻译人员: Jian Zhipeng 校对人员: Ru Zha

The human eye is an amazing mechanism,

人的眼睛是一种十分神奇的结构，

able to detect anywhere from a few photons to direct sunlight,

它能够探查任何地方 小到几个光子，大到直射的阳光，

or switch focus from the screen in front of you

且能在三分之一秒内，将焦点

to the distant horizon in a third of a second.

从你面前的屏幕切换到遥远的地平线。

In fact, the structures required for such incredible flexibility

事实上，由于眼睛如此灵巧，

were once considered so complex

其结构曾被认为极其复杂，

that Charles Darwin himself acknowledged that the idea of there having evolved

以至于达尔文意识到眼睛进化的程度

seemed absurd in the highest possible degree.

高得离谱。

And yet, that is exactly what happened, starting more than 500 million years ago.

而眼睛的进化正是如此， 这早在五百万年前就开始了。

The story of the human eye begins with a simple light spot,

有关人类眼睛的故事， 开始于一个极其简单的感光点，

such as the one found in single-celled organisms,

正如在诸如眼虫等 单细胞生物体中

like euglena.

发现的一样。

This is a cluster of light-sensitive proteins

它是连接在生物体鞭毛上的

linked to the organism's flagellum,

一簇光敏蛋白，

activating when it finds light and, therefore, food.

当感受到光亮时该蛋白被激活， 因而会使鞭毛游动来获取食物。

A more complex version of this light spot can be found in the flat worm, planaria.

扁形动物中的涡虫 则拥有更复杂的感光点结构。

Being cupped, rather than flat,

其不是扁平的而是凹陷成杯状，

enables it to better sense the direction of the incoming light.

这使涡虫能更好的感知 入射光线的方向。

Among its other uses,

除了其它用途外，

this ability allows an organism to seek out shade and hide from predators.

此种结构使得生物体可以 寻找遮蔽处并躲避捕食者。

Over the millenia,

过去几千年，

as such light cups grew deeper in some organisms,

在某些生物体中， 这种杯状感光体变得愈发凹陷，

the opening at the front grew smaller.

且前端的开口处变得越来越小。

The result was a pinhole effect, which increased resolution dramatically,

此变化的结果便是“针孔效应”， 这使得分辨率极大地提高，

reducing distortion by only allowing a thin beam of light into the eye.

并只让一束细光能够射入眼睛， 以此来降低失真率。

The nautilus, an ancestor of the octopus,

章鱼的祖先之一——鹦鹉螺

uses this pinhole eye for improved resolution and directional sensing.

用这样的针孔眼来提高 分辨率和方向感。

Although the pinhole eye allows for simple images,

虽然针孔眼能看到简单图像

the key step towards the eye as we know it is a lens.

但正如我们所知， 演化成眼睛的关键是晶状体。

This is thought to have evolved

这里认为是由

through transparent cells covering the opening to prevent infection,

透明细胞包裹住前端开口处以防感染，

allowing the inside of the eye to fill with fluid

并使得眼球内部能够充满液体，

that optimizes light sensitivity and processing.

以优化光敏感度和对光的处理。

Crystalline proteins forming at the surface

在眼睛表面形成的蛋白质结晶，

created a structure that proved useful

形成了一个被人们证实为有用的结构

in focusing light at a single point on the retina.

此结构使得光线聚焦在视网膜上的一个点。

It is this lens that is the key to the eye's adaptability,

这晶状体在眼睛视物时起到了关键的调节作用，

changing its curvature to adapt to near and far vision.

它通过改变自身的曲率来调节近景及远景。

This structure of the pinhole camera with a lens

这种针孔摄像头加以晶状体的结构，

served as the basis for what would eventually evolve into the human eye.

是最终进化为人眼的基础。

Further refinements would include a colored ring, called the iris,

进一步的进化改良包括：一个彩色的圆环——虹膜，

that controls the amount of light entering the eye,

它控制进入眼睛的光线数量；

a tough white outer layer, known as the sclera,

一个坚韧的白色的外层，也就是所谓的巩膜，

to maintain its structure,

用来保持眼睛的结构；

and tear glands that secrete a protective film.

以及泪腺，来分泌保护性的薄膜。

But equally important

而同等重要的是，

was the accompanying evolution of the brain,

伴随眼睛一同进化的大脑，

with its expansion of the visual cortex

用其不断扩大的视觉皮层，

to process the sharper and more colorful images it was receiving.

来加工它所接收到的更清晰更多彩的图像。

We now know that far from being an ideal masterpiece of design,

现在我们知道了，眼睛并不是想象中大师级的设计，

our eye bares traces of its step by step evolution.

我们的眼睛拥有其一步步的进化过程。

For example, the human retina is inverted,

举个例子，人类的视网膜是倒置的，

with light-detecting cells facing away from the eye opening.

其上布满了背向眼睛前端的感光细胞。

This results in a blind spot,

这形成了生理盲点，

where the optic nerve must pierce the retina

在盲点处，视神经必须穿过过视网膜

to reach the photosensitive layer in the back.

来到达其背后的感光层。

The similar looking eyes of cephalopods,

头足纲动物拥有相似的眼睛

which evolved independently,

他们的眼睛是独立进化的，

have a front-facing retina, allowing them to see without a blind spot.

有着一个朝前的视网膜，使得他们的视野没有盲区。

Other creatures' eyes display different adaptations.

其他生物的眼睛也呈现出了不同的适应性。

Anableps, the so called four-eyed fish,

比目鱼，也就是所谓的四眼鱼，

have eyes divided in two sections for looking above and under water,

拥有分成两区的眼睛，一只用来看水上，一只用来看水下，

perfect for spotting both predators and prey.

让它们能够很好的发现捕食者以及猎物。

Cats, classically nighttime hunters, have evolved with a reflective layer

猫——经典的夜间捕食者，进化出了反射层，

maximizing the amount of light the eye can detect,

大大增强了眼睛对光的捕捉能力，

granting them excellent night vision, as well as their signature glow.

这赋予了猫科动物出色的夜视功能和他们标志性能发光的猫眼。

These are just a few examples of the huge diversity of eyes in the animal kingdom.

这些只是动物王国里，种类繁多的眼睛中的几个范例

So if you could design an eye, would you do it any differently?

所以，如果你能设计出一种眼睛，你会造得有所不同吗？

This question isn't as strange as it might sound.

这问题并没有听起来那么奇怪。

Today, doctors and scientists are looking at different eye structures

目前，医生和科学家在研究不同的眼睛结构

to help design biomechanical implants for the vision impaired.

来帮助设计出为视障患者移植所需的仿生植入物。

And in the not so distant future,

并且在不远的将来，

the machines built with the precision and flexibilty of the human eye

机器制造出的精确又灵活的眼睛，

may even enable it to surpass its own evolution.

也许甚至能超越眼睛本身的进化程度。