The evolution of the human eye - Joshua Harvey

人眼的演進 - 約書亞哈維

譯者: 毓翔 王 審譯者: Simon Sun

The human eye is an amazing mechanism,

人類的眼睛是一個了不起的機制

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

能夠檢測任何位置， 小到幾個光子，大到直射的陽光

or switch focus from the screen in front of you

而且能在三分之一秒內

to the distant horizon in a third of a second.

把焦點從你面前的屏幕 切换到遙遠的地平線

In fact, the structures required for such incredible flexibility

事實上，由於眼睛的構造如此靈巧

were once considered so complex

曾被認為太過複雜

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

以致達爾文意識到眼睛進化的速度

seemed absurd in the highest possible degree.

高得太離譜

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

而眼睛的進化正是如此， 這在五百萬年前就已經開始了

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

有關人類眼睛的故事， 開始於一个極其簡单的感光點

such as the one found in single-celled organisms,

正如眼蟲這種單细胞生物體中

like euglena.

發現的一樣

This is a cluster of light-sensitive proteins

它是連接在生物體鞭毛上的

linked to the organism's flagellum,

一群光敏蛋白

activating when it finds light and, therefore, food.

當感受到光亮時該蛋白會被激活， 因而會使鞭毛游動來獲取食物

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

扁形動物中的渦蟲 則擁有更複雜的感光點結構

Being cupped, rather than flat,

其不是扁平的而是凹陷成杯狀

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

這使渦蟲能更好的感知 入射光線的方向

Among its other uses,

除了其它用途外

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

此結構使得生物體可以 尋找遮蔽處並躲避捕食者

Over the millenia,

過去幾千年

as such light cups grew deeper in some organisms,

在某些生物體中， 這種杯狀感光體變得更加凹陷

the opening at the front grew smaller.

且前端的開口變得越來越小

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

此變化的結果便是“針孔效應”， 這使分辨率極大地提昇

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

並只讓一束细光能夠射入眼睛， 以此來降低失真率

The nautilus, an ancestor of the octopus,

章魚的祖先之一「鸚鵡螺」

uses this pinhole eye for improved resolution and directional sensing.

利用這樣的針孔眼来提高 分辨率和方向感

Although the pinhole eye allows for simple images,

雖然針孔眼能看到簡單圖像

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

但正如我們所知， 演化成眼睛的關建是晶狀體

This is thought to have evolved

這裡認為是由

through transparent cells covering the opening to prevent infection,

透明細胞包裹住前端開口處來防止感染

allowing the inside of the eye to fill with fluid

並使得眼球内部能夠充滿液體

that optimizes light sensitivity and processing.

以優化光敏感度和對光的處理

Crystalline proteins forming at the surface

而在眼睛表面形成的蛋白質结晶

created a structure that proved useful

形成了一個重要结構，而人們證實了

in focusing light at a single point on the retina.

此結構在將光線聚焦在視網膜 上的一點時會起到作用

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

正是晶狀體在調節眼睛看物體時 起到了關鍵作用

changing its curvature to adapt to near and far vision.

其通過改變自身的曲率來 調節眼睛看近景和遠景

This structure of the pinhole camera with a lens

這種針孔攝像頭加上晶狀體的結構

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

最終演變為人眼的基礎

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

進一步的進化改良包括： 一個彩色的圓環——虹膜

that controls the amount of light entering the eye,

它控制進入眼睛的光線数量；

a tough white outer layer, known as the sclera,

一個堅韌白色的外層， 也就是所謂的鞏膜

to maintain its structure,

用來保持眼睛的結構；

and tear glands that secrete a protective film.

以及淚腺， 來分泌具有保護性的薄膜

But equally important

然而同樣重要的是

was the accompanying evolution of the brain,

伴隨眼睛一起進化的大腦

with its expansion of the visual cortex

用其不斷擴大的視覺皮層

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

來處理接收到的 更清晰多彩的圖像

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

現在我們知道的， 遠不如想像中大師級的傑作

our eye bares traces of its step by step evolution.

我們的眼睛擁有其一步一步的進化過程

For example, the human retina is inverted,

舉個例子，人類的視網膜是倒置的

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

其上方布滿了背向眼睛前端的感光细胞

This results in a blind spot,

這形成了盲點

where the optic nerve must pierce the retina

在盲點處，視神經必須穿過視網膜

to reach the photosensitive layer in the back.

來到達其背后的感光層

The similar looking eyes of cephalopods,

頭足綱動物擁有類似的眼睛

which evolved independently,

他們的眼睛是獨立進化的

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

有著一個朝前的視網膜， 使得牠們的視野没有盲區

Other creatures' eyes display different adaptations.

其他生物的眼睛也呈現出了不同的適應性

Anableps, the so called four-eyed fish,

Anableps，即所謂的四眼魚

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

擁有分成兩區的眼睛， 一個用來看水上，一個用來看水下

perfect for spotting both predators and prey.

讓牠们能夠很好的發現 捕食者及獵物

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

貓——經典的夜間捕食者， 進化出了反射層

maximizing the amount of light the eye can detect,

大大增強了眼睛對光的捕捉能力

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

這給予了貓科動物出色的夜視能力， 以及他们標誌性會發光的貓眼

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

這些只是動物王國裡， 種類繁多的眼睛中的幾個範例

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

所以，如果你能設計出一種眼睛， 你會設計得有所不同嗎？

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

這問题並没有聽起來那麼奇怪

Today, doctors and scientists are looking at different eye structures

目前，醫生和科學家正在研究不同的眼睛結構

to help design biomechanical implants for the vision impaired.

來幫助視障患者設計出 移植所需的仿生學植入物

And in the not so distant future,

並且在不遠的將來

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

機器制造出的精確靈活的眼睛

may even enable it to surpass its own evolution.

也許能夠超越眼睛本身的進化程度