Why do fingers become pruney? - Mark Changizi

泡水手指上的皺摺：一篇關於抓取物品的故事 - Mark Changizi

Transcriber: Andrea McDonough Reviewer: Jessica Ruby

譯者: Jephian Lin 審譯者: Jessie Lee

There are all sorts of things

有許多

that happen every day

天天發生的事物，

that might make you ask,

你可能都會問：

"Why?

「為什麼？

Why do we drive on a parkway

為什麼我們在停車道上開車 （譯註：英文 parkway 指的是大公路。）

and park on a driveway?

而在開車道上停車？ （譯註：而 driveway 指的是私人車道。）

Why does my hair get frizzy when it's humid?

為什麼天氣潮濕的時候頭髮會變得毛燥捲曲？

And why do my fingers get all pruney when they're wet?"

為什麼手指泡水的時候會變皺？」

Often we simply can't know the answers to these questions.

很多時候我們並不知道這些問題的答案。

But progress can often be made,

不過還是有些進展，

and, when it comes to your pruney fingers,

在手指變皺這方面

scientists have a few interesting ideas.

科學家有些有趣的想法。

The story here begins with an observation

這要從 1930 年代裡

made in the 1930s in the emergency room.

一項急診室裡觀察到的現象說起。

Doctors noticed that patients

當時的醫生發現

with nerve damage to their hands

手部神經受損的病人

did not get pruney fingertips

並不會像我們洗澡時那樣 手指前端會有變皺的現象。

like most of us do in a bath,

並不會像我們洗澡時那樣 手指前端會有變皺的現象。

which might make you wonder,

這可能會讓你好奇說：

"Why would primates want wrinkly fingers,

「為什麼靈長類在雨天或潮濕時

presumably when it's rainy or dewy?"

會需要有皺摺的手指？

What could this trait be for?

這項生物特徵的用處是什麼？

What if these wrinkles functioned like rain treads?

會不會這指皺摺的功能和輪胎凹槽一樣呢？」

Think about car tires.

想想看車子的輪胎，

When the ground is dry,

當路面是乾的時候，

it's generally best to have smooth tires,

最好是用平滑的胎面，

and race cars do.

就像賽車那樣。

Smooth tires means more rubber

平滑胎可以讓較多的橡膠

or surface area in contact with the road,

或是輪胎表面和地面接觸，

which gives them better grip.

這會增加抓地力。

But in rainy and muddy conditions,

但是在雨天或泥地裡，

it's a different story,

這又是另外一回事，

and here's where treads come into play.

也就是輪胎凹槽派上用場的時候了。

Treads reduce the amount of rubber on the road,

凹槽可會減少橡膠和路面接觸的面積，

but they help channel out water when it rains,

而在雨天時幫助排出雨水、

lowering the risk of hydroplaning.

降低水面打滑的風險。

Well, if your fingers really are like rain treads,

嗯，如果手指真的就像輪胎凹槽那樣，

you should be able to predict

你應該猜得出

the optimal shape for them, right?

它們效果最佳時的樣子，對吧？

So, what would the predicted wrinkle shapes be?

那麼，意料中的皺摺應該是什麼樣子？

That is, are our prunes actually the right shape

也就是，我們手指的皺摺真的就像

to be rain treads?

輪胎凹槽那樣嗎？

Let's take a detour into rivers.

讓我們到河裡去瞧瞧。

When we think of river networks,

當想到河流網絡的時候，

we usually imagine lots of smaller river channels

我們通常會想到許多較小的河道

joining to make larger river channels downstream,

匯聚在一起形成較大的下游河道，

which is what happens in concave basins.

在向下凹的流域裡的確是這樣的。

In these cases, the divides,

在這情況下，分水嶺 ─

the regions between the river segments,

也就是河道與河道間的區域，

are disconnected from one another

形成分歧

and diverge away from one another uphill.

並向上分佈在地勢較高處。

But river networks look fundamentally different

但是在向上凸的海岬或隆起處， 河流網絡就截然不同了。

on convex promontories or protrusions.

但是在向上凸的海岬或隆起處， 河流網絡就截然不同了。

Here, the river channels are disconnected from one another

在這裡，河道會被劃分開來

and diverge away from one another downstream,

然後分佈在各個下游區，

not very river-like.

跟平常的河流不太一樣。

In these cases, it's the divides

在這情況下，這些分水嶺

that link together to form a tree,

像樹的形狀般連結在一起，

with its trunk uphill at the top of the promontory.

隆起處頂端就是樹幹。

Here, it's the divides that look more traditionally river-like.

在這裡，反而是分水嶺比較有河流的樣子。

If our pruney fingers are drainage networks,

如果泡水手指上的皺摺是個排水系統、

designed to channel out water when they grip,

是設計來在抓取物品時引導水流，

then we expect to find similar shapes on our fingers

那我們可以料想得到那皺摺 會有類似河流的形狀。

as we find out there among rivers.

那我們可以料想得到那皺摺 會有類似河流的形狀。

There should be a tree network of divides,

應該會有分水嶺或山脊的樹狀網絡，

or ridges, with their trunk near the top of the fingertip

而樹幹部份應該在指尖附近、

and with their more leaky parts

各排水凹槽

reaching out downhill, away from the tip.

則自頂端向手指下方延伸。

The channels themselves,

這些在抓取物品時用來引導水流的水道，

through which the water is channeled during a grip,

這些在抓取物品時用來引導水流的水道，

should not connect to one another,

應該沒有相連

and instead should diverge away from one another downhill.

且各自向下分散。

If pruney fingers are rain treads,

如果手指皺摺是輪胎凹槽，

then they should look like the river networks

那它們就應該看起來像是

on convex promontories.

隆起處的河流網絡。

In fact, that's exactly the morphology

事實上，這正是我們

we find among pruney fingers!

在手指皺摺上發現的結構形態！

When we grip, then,

當我們抓取物品時，

our pruney wrinkles really do channel out the water.

那些李子乾狀的皺摺的確可以將水排出。

But does it actually help us grip?

但它真的對抓取物品有利嗎？

New behavioral experiments have shown that they do.

一些新的行為實驗證明了這點。

In a task where subjects had to grasp wet marbles

在一項研究中，受試者必需抓取濕的大理石

and move them through a hole and out the other side,

並將大理石擲到洞的另一邊，

those with pruney fingers finished the task

手指有皺摺的那組 比起平滑手指的對照組明顯快了許多。

significantly faster than those with smooth fingers.

手指有皺摺的那組 比起平滑手指的對照組明顯快了許多。

Pruney fingers not only ought to enhance grip in wet conditions

手指皺摺不只是「看似會」在潮濕條件下增加抓取能力，

but do.

而是「真的會」。

So, pruney fingers may be a crucial part

所以手指皺摺是靈長類的一項重要生物特徵。

of the primate repertoire.

所以手指皺摺是靈長類的一項重要生物特徵。

Maybe, once primates lost their claws

也許，在靈長類選擇指甲

in favor of fingernails,

而失去尖爪的時候，

rain treads were needed to deal

這些凹槽就派上用場

with the especially challenging,

來應付這具挑戰性、

often wet, grip-heavy forest habitats.

時常潮濕、又十分仰賴抓取力的森林棲息地。

By looking closely at the mysteries in our world

藉由深入了解我們世界的奧妙

and trying to find things that look similar,

並試著找尋類似的模式，

like our wet fingers and rain treads,

比如說泡水的手指和輪胎凹槽，

we can come up with ideas about what's happening.

我們就會對發生什麼事有一些想法。

And that's a good way to think about

而這對生活中五花八門的問題來說 也是一種不錯的思考方式。

all sorts of questions in life, too.

而這對生活中五花八門的問題來說 也是一種不錯的思考方式。