Why do cats have vertical pupils? - Emma Bryce

譯者: Regina Chu 審譯者: Yi-Ping Cho (Marssi)

Peering into the eyes of different animals,

若你仔細端詳不同動物的眼睛

you’ll see some extraordinarily shaped pupils.

你會看到一些意想不到的瞳孔形狀

But why?

但是為什麼會這樣？

It turns out that pupil shape is a powerful indicator

原來瞳孔形狀是一種強力指標

of what role an animal plays in its ecosystem.

顯示出這種動物在生態系中 所扮演的角色

Pupils mark the hollow opening in the iris,

瞳孔是虹膜的開口

the eye’s band of pigmented muscle.

虹膜就是眼睛那圈帶色素的肌肉

They’re the portholes through which light enters the eye,

瞳孔是讓光線進入眼睛的窗戶

where it then strikes the retina and activates light-sensitive cells,

光線由此打擊視網膜 活化感光細胞

setting the process of vision in motion.

啟動目視過程

Pupils are black because most of the light that enters them is absorbed.

瞳孔是黑色的 因為大多數進入的光線都被吸收

Their size changes in response to brightness,

瞳孔的大小會隨著亮度

as well as certain drugs and emotional and mental states—

某些藥物及情緒和精神狀態而改變

but their basic form varies greatly among species.

但是不同物種的瞳孔基本形狀差異很大

House cats, for one, are twilight hunters with vertically elongated pupils.

舉家貓為例，牠們在曙暮光下狩獵 有垂直拉長的瞳孔

In the dark, these structures expand dramatically,

在黑暗中，這個結構急劇擴張

taking in the available light.

讓更多的光線進入

When it’s bright, they shrink into slits.

天色大亮時，它們就縮成狹縫

In fact, cat pupils are so flexible that their maximum area is 135 times greater

事實上貓的瞳孔非常靈活

最大的面積比最小的面積大 135 倍

than their minimum area—

whereas our pupils only shrink and expand 15-fold.

而我們的瞳孔只能縮放 15 倍

And because of how the slit pupil takes in light,

這種狹縫瞳孔接收光的方式

it creates sharp, vertical contours.

會使瞳孔變成尖銳垂直的形狀

When the cat’s brain processes the visuals from each eye,

當貓的腦部處理 來自兩隻眼睛的視覺影像時

the small but sharp differences between them

兩者之間微小卻清晰的差別

help the cat judge the precise distance of its target.

會幫助貓判斷目標的準確位置

In fact, many other ambush hunters also have vertically elongated pupils—

實際上，許多埋伏型獵獸 也有垂直拉長的瞳孔

but mainly those whose eyes are located closer to the ground.

不過最主要還是 眼睛更靠近地面的動物

This may be because these pupils are especially useful in perceiving objects

這可能是因為這種瞳孔

at the relative short distances these animals tend to hunt.

對近距離捕獵特別有用

The world looks very different from behind the horizontally elongated pupils

但是從水平拉長的瞳孔 看這個世界就非常不一樣

of many grazing and browsing animals, like goats.

許多牧食和覓食的動物 如山羊，就有這種瞳孔

These pupils, situated on either side of the head,

這種瞳孔位於頭的兩側

let horizontal bands of light in that give the goat a near-360-degree view

讓水平光進入 使山羊幾乎有 360 度的視角

and provide it with sharp, horizontal images.

並提供清晰的水平影像

This helps goats detect any disruption to the horizon—

這幫助山羊偵測水平面上的干擾

alerting them to potential predators— while still enabling them to see ahead

提醒牠們注意潛在的掠食者

並在逃跑時還能看到前方並偵測障礙物

and detect obstacles as they make their escape.

In fact, goats always keep their pupils aligned with the horizon,

實際上山羊的瞳孔總是與水平線對齊

rotating their eyeballs in their sockets as they move their heads up and down.

當牠們上下移動頭時 就在眼窩中轉動眼球

Meanwhile, nocturnal geckos have pupils that shrink into slits

同時，夜行的壁虎在比較亮的時候

studded with pinholes in higher light conditions.

會把佈滿針孔型小洞的瞳孔縮成狹縫

Each pinhole projects a separate, sharp image onto the geckos retina.

每個小針孔都會在壁虎的視網膜上 投射出清晰的影像

Scientists think that comparing these different inputs

科學家認為比較輸入影像的不同點

might help the gecko judge distance without having to move.

可能有助於壁虎判斷距離，無需移動

And while they might have fooled you,

而有些動物可能騙到你了

mantises and other insects and crustaceans have “pseudopupils.”

螳螂、其他昆蟲和甲殼類動物 其實有「偽瞳孔」

These aren’t optical structures;

它們不是視覺構造

they’re optical illusions experienced by the observer.

它們是觀察者所經歷的視錯覺

Mantises have compound eyes composed of thousands of light-sensing units.

螳螂的複眼上有上萬個感光小眼

When some are aimed at you, they appear black

當某些小眼對準你時 它們看起來是黑色的

because they’re absorbing most wavelengths of incoming light—

因為它們吸收了大部分入射光的光波

but there’s no actual opening.

但是沒有實際的開口

So, why do we have round pupils?

那，為什麼我們有圓形的瞳孔？

Elongated pupils help sharpen certain dimensions of an animal's vision.

細長的瞳孔有助於提高 動物的某些視覺範圍

But scientists think that, for animals like us with circular pupils,

但是科學家認為，像我們這種 有圓形瞳孔的動物

this is a lower priority.

這不太重要

Instead of seeing some elements of a scene in extreme focus,

與其把一個畫面的某些成分看得超清楚

we see a larger picture in relative detail,

我們反而喜歡看更大的畫面 細節差不多就好

which enables more general skills of observation.

這樣能讓整體的觀察能力更好

This may be especially helpful for foragers looking for food,

這對覓食者可能特別有用

hunters eyeballing and chasing their prey,

獵獸要緊盯並追逐獵物

and social animals recognizing other faces.

群居動物則要能識別其他人的長相

As we peer at different pupils, patterns emerge.

當我們端詳不同的瞳孔，會觀察到模式

And yet there are exceptions.

但是還是有例外

For example, Pallas’s cats and mongooses are both small ambush predators,

例如兔猻及貓鼬 都是小型的伏擊型掠食者

but the Pallas’s cat has round pupils and mongooses have goat-like pupils.

但是兔猻有圓的瞳孔 貓鼬卻有山羊型的瞳孔

And we’ve only explored a few pupil shapes.

而且我們才看了幾種瞳孔形狀

Other animals have crescent- or heart-shaped pupils.

有些動物有弦月形或心形的瞳孔

And the cuttlefish has perhaps some of the most bizarre:

墨魚大概是最奇怪的

their pupils are circular in the dark, but W-shaped in the light.

牠們的瞳孔在黑暗中是圓的 明亮時卻呈現 W 形

So, what’s going on here?

所以這到底是怎麼回事？

Well, wouldn’t we all like to know?

這，我們也很想知道