The surprising reason zebras have stripes - Cella Wright

譯者: Lilian Chiu 審譯者: Zoe Walmsley

When an English aristocrat rode through London in a zebra-drawn carriage,

當某位英國貴族乘坐 由斑馬拉的馬車穿越倫敦時，

he embodied a dream decades in the making,

一個醞釀了數十年的夢想終於成真──

borne from European efforts to dominate the African continent.

非洲大陸被歐洲控制。

But 19th century European colonists faced big problems

十九世紀的歐洲殖民者

在試圖控制擁有的遼闊非洲領土時， 並非沒有碰上挑戰，

as they tried to control the sprawling African territories they’d claimed,

one of which was biting flies.

其中之一是會叮咬的蒼蠅。

These pests could extract half a liter of horse blood daily

這些害蟲每天可以吸取半公升的馬血，

while transmitting fatal diseases that devastated domestic horses,

同時傳播致命的疾病給馴養的馬匹，

leaving colonial powers reliant on thousands of humans to transport goods.

迫使殖民列強改以 數千名人力來運送貨物。

Zebras, however, appeared immune to the same pitfalls as horses.

然而，斑馬似乎對馬碰到的問題免疫。

The German Empire deemed them “predestined for the use of military needs,”

德意志帝國因此認為牠們 「注定要用於軍事需求」，

and undertook the task of domesticating them.

並展開了馴化牠們的任務。

Around 1900, former German colonial army officer Fritz Bronsart von Schellendorff

1900 年左右，前德國殖民軍官

弗里茲‧布朗札特‧馮‧謝倫多夫

placed himself at the mission’s helm.

接下了這個重責大任，

But he severely underestimated the project.

但他嚴重低估了這項計畫。

And soon enough,

因為沒多久，

the question of why domesticating zebras was proving so difficult

他就發現斑馬為何難以馴化的問題

joined another longstanding mystery:

與另一個歷史悠久的謎有關係：

namely, why zebras had such conspicuously striped coats—

那就是，為什麼斑馬有 如此顯著的條紋皮毛──

a matter that perplexed prominent scientists—

一個困惑了眾多科學家們──

and went on to fuel decades of debate.

且讓他們爭論數十年的問題。

To understand zebras’ more distinctive qualities,

要了解斑馬更多的特質，

we should start with the big picture.

我們應該從大局談起。

Zebras belong to the same family as horses and donkeys.

斑馬與馬和驢子屬於同一個家族。

After their lineage entered Africa,

在牠們的血統進入非洲後，

they evolved into the three zebra species that exist today,

牠們演化為現今存在的三種斑馬，

living in social herds in eastern and southern Africa,

以群居方式生活在非洲的東部和南部，

grazing on grasses and evading fierce predators.

以草為食，並躲避兇猛的肉食性動物。

Scientists have speculated extensively about zebra striping,

科學家對斑馬的條紋 有各式各樣的推測，

but not all theories have held up.

但並非所有理論都能成立。

For example,

例如，有個說條紋具有社交功能的假設

the hypothesis that striping has a social function seems unlikely because,

就不太可能成立，

while every zebra does have unique patterning,

因為，雖然每隻斑馬 確實都有獨一無二的花紋，

other equids have no trouble identifying individuals in their herd without it.

但那些沒有斑紋的馬科動物 也沒有辨識彼此的問題。

Some have theorized that the pattern helps zebras stay cool in direct sunlight,

有個理論說斑馬的花紋 讓斑馬在直射的陽光下保持涼爽，

with the heat differential between their black and white stripes

因為黑白色條紋的熱差 會產生冷卻的氣流。

generating cooling air currents.

But when scientists tracked the air movements around sunlit zebra hides,

但是科學家實際測量 陽光下斑馬毛皮上的氣流時，

they saw no such effect.

並沒發現這種效果。

Many have also wondered if the patterning works as camouflage

許多人懷疑這種圖案 有迷彩偽裝的作用，

or somehow confuses or dazzles predators—

或許能讓肉食性動物混淆或眼花──

perhaps evoking a tangle of tree trunks

也許以為看到的是錯綜複雜的樹幹，

or creating uncertainty around where the zebra’s body starts and ends.

或甚至斑馬的頭尾變得難以辨識。

But hyenas and lions probably see zebras as gray until they're in close range,

土狼和獅子距離斑馬很遠時， 看到的斑馬是灰色的，

靠得夠近才看得到斑紋，

where they can also hear and smell them.

同時，也就能聽到和聞到牠們了。

Lions can likely also identify their outlines just as easily as they can

獅子也能很容易辨識出斑馬的輪廓，

跟其他不那麼顯目的獵物一樣容易。

other, less flamboyantly patterned prey.

And given how frequently lions capture zebras,

而且既然獅子經常能捕捉到斑馬，

it doesn't seem like they're all that confused.

可見斑馬的紋路並沒成功迷惑獅子。

One hypothesis that does pack a lot of promise

有一個假設比較被看好，

concerns those biting flies that horses couldn’t handle.

它和馬類無法對付的蒼蠅有關。

Zebras have shorter hair than other grazers in their regions,

跟其他同一區的草食動物相比， 斑馬的毛明顯短很多，

possibly making them more vulnerable to the flies’ probing proboscises.

在面對蒼蠅的長長的口器時 這點讓他們異常脆弱，

So, perhaps striping somehow acts protectively.

所以，條紋或許有某種保護作用。

Testing this hypothesis,

要驗證這個假設，

one experiment found that a certain kind of biting fly

有一項實驗發現，有某種叮咬的蒼蠅

avoided horses covered in striped and checked rugs,

會避開披著條紋和格紋毯子的馬，

compared to those in solid grey.

而選擇叮咬披上純灰色毯子的馬。

Another documented biting flies circling horses, zebras,

另一項實驗的記錄顯示， 叮咬蒼蠅會在馬、斑馬，

and horses clad in zebra print equally—

和披著斑馬條紋毯子的馬 周圍繞飛的機率相當──

but landing on zebra-y areas only about a quarter as much.

但降落在斑馬條紋區域上的 機率卻只有四分之一。

Biting flies also generally approached zebras at higher speeds

叮咬的蒼蠅通常會高速接近斑馬，

and didn't decelerate as usual,

且不像平常那樣減速，

causing clumsy overshoots and crash landings.

導致笨手笨腳地錯過目標 或降落得跌跌撞撞。

It seems that zebra stripes— and other graphic patterns—

似乎，斑馬的條紋── 及其他圖形的花紋──

interfere with how biting flies process visual information

似乎會干擾叮咬蒼蠅 在降落時處理視覺資訊，

to position themselves when landing,

limiting their blood-sucking and disease-transmitting opportunities.

減少牠們吸血和傳播疾病的機會。

But zebras aren't just good at keeping biting flies off their backs.

但是斑馬不只是擅長 讓叮咬蒼蠅遠離牠們的背。

Around 1900, Bronsart founded an experimental ranch near Mount Kilimanjaro

1900 年左右，

布朗札特在吉力馬札羅山 附近開了一個實驗牧場，

to capture and cross-breed zebras with other equids.

捕捉斑馬並與其他馬科動物交配。

Things didn’t go as planned—

事情並沒有按計畫發展──

in part because zebras have a robust set of defensive fight and flight adaptations.

部分原因是因為斑馬有一套 很強的戰與逃防禦機制。

Most are capable of running within an hour of birth,

大部分在出生後一小時就能奔跑，

and they’re equipped with fierce bites and kicks strong enough to kill a lion.

且具有兇猛的咬合力 和足以踢死獅子的腳力。

Bronsart’s operation was also unprepared to meet zebras’ needs.

布朗札特的運作 也無法滿足斑馬的需求。

Those Bronsart did gather, which he paid Indigenous people to wrangle,

即使那些布朗札特付錢 請原住民抓到的斑馬

couldn’t produce enough milk for their calves.

也無法產出足夠的奶給小斑馬喝。

Within a single year, Bronsart had burned through a five year budget

單單一年，布朗札特 就燒光了五年的預算，

and dozens of the zebras he held in captivity were dead.

而農場上的數十隻斑馬也死得差不多。

Attempts at zebra domestication had failed miserably,

馴化斑馬的嘗試慘遭失敗，

leaving those rare instances of zebra taming largely to black-and-white history.

讓那極少數馴養斑馬的例子 基本上成了黑白歷史。