There are all sorts of things that happen every day that might make you ask, "Why?
每天都会发生各种事情让你产生疑问：为什么？
Why do we drive on a parkway and park on a driveway?
为什么我们在马路上开车，而在停车道上停车？
Why does my hair get frizzy when it's humid?
为什么天气潮湿的时候头发会变得卷曲？
And why do my fingers get all pruney when they're wet?"
为什么手指泡水的时候会变皱？
Often we simply can't know the answers to these questions.
很多时候我们并不知道这些问题的答案。
But progress can often be made, and, when it comes to your pruney fingers, scientists have a few interesting ideas.
不过还是有些进展，在手指变皱这方面，科学家有些有趣的想法。
The story here begins with an observation made in the 1930s in the emergency room.
这要从20世纪30年代时一项急诊室里观察到的现象说起。
Doctors noticed that patients with nerve damage to their hands did not get pruney fingertips like most of us do in a bath,
当时的医生发现，手部神经受损的病人，并不会像我们洗澡时那样，手指前端会有变皱的现象。
which might make you wonder, "Why would primates want wrinkly fingers, presumably when it's rainy or dewy?"
这可能会让你感到好奇：“为什么灵长类在雨天或湿度大时，手指会有褶皱呢？”
What could this trait be for?
这项生物特征的用处是什么？
What if these wrinkles functioned like rain treads? Think about car tires.
褶皱的功能会不会和轮胎凹槽一样呢？想一想车子的轮胎。
When the ground is dry, it's generally best to have smooth tires, and race cars do.
当路面是干的时候，最好是用平滑的胎面，就像赛车那样。
Smooth tires means more rubber or surface area in contact with the road, which gives them better grip.
平滑胎可以让较多的橡胶或是轮胎表面和地面接触，这会增加抓地力。
But in rainy and muddy conditions, it's a different story, and here's where treads come into play.
但是在雨天或泥地里，就又是另外一回事了，也就是轮胎凹槽派上用场的时候了。
Treads reduce the amount of rubber on the road,
凹槽会减少橡胶和路面接触的面积，
but they help channel out water when it rains, lowering the risk of hydroplaning.
但在下雨时可以帮助轮胎排水，降低轮胎打滑的风险。
Well, if your fingers really are like rain treads,
嗯，如果手指真的就像轮胎凹槽那样，
you should be able to predict the optimal shape for them, right?
你应该猜得出它们效果最佳时的样子，对吧？
So, what would the predicted wrinkle shapes be?
那么，意料中的皱褶应该是什么样子呢？
That is, are our prunes actually the right shape to be rain treads?
也就是说，我们手指上的皱褶真的像轮胎凹槽那样吗？

Let's take a detour into rivers. When we think of river networks,
让我们到河里去瞧瞧。当想到河流网络的时候，
we usually imagine lots of smaller river channels joining to make larger river channels downstream, which is what happens in concave basins.
当我们想到河网分布时，通常会想到有许多较小的河道汇聚而成相对较大的下游河道，在地形向下凹陷的流域里就是这样的。
In these cases, the divides, the regions between the river segments,
在这种情况下，分水岭，也就是让两个相邻的水域形成分岔，
are disconnected from one another and diverge away from one another uphill.
向上分布在地势较高处。
But river networks look fundamentally different on convex promontories or protrusions.
但是向上凸起的海岬或隆起处，河网分布就截然不同了。
Here, the river channels are disconnected from one another and diverge away from one another downstream, not very river-like.
在这里，河道会被划分开来，然后分布在各个下游区，跟平常的河流不太一样。
In these cases, it's the divides that link together to form a tree, with its trunk uphill at the top of the promontory.
这种情况下的分水岭像树的形状一样连在一起，顶端隆起的部分为树干。
Here, it's the divides that look more traditionally river-like.
在这里，反而是分水岭看起来像河流一样。
If our pruney fingers are drainage networks, designed to channel out water when they grip,
假设我们手上的皱褶是排水系统，是设计来在抓取物品时排出水流，
then we expect to find similar shapes on our fingers as we find out there among rivers.
那我们可以想到那些褶皱应该和河流的形状相似。
There should be a tree network of divides, or ridges,
它们应该有树型的分水岭或山脊，
with their trunk near the top of the fingertip and with their more leaky parts reaching out downhill, away from the tip.
树干部分应该接近指尖，还有更多的排水皱褶自顶端向手指下方延伸。
The channels themselves, through which the water is channeled during a grip,
这些在抓取物品时用来引导水流的水道，
should not connect to one another, and instead should diverge away from one another downhill.
应该是不相互连接的，而是各自向下分散。
If pruney fingers are rain treads, then they should look like the river networks on convex promontories.
如果手指皱褶是轮胎凹槽，那它们看起来应该像是隆起处的河网。
In fact, that's exactly the morphology we find among pruney fingers!
事实上，这正是我们在手指褶皱上发现的形态！
When we grip, then, our pruney wrinkles really do channel out the water.
当我们拿起东西的时候，褶皱可以帮助我们排掉水分。
But does it actually help us grip? New behavioral experiments have shown that they do.
但是，这真的有利于拿取物品吗？一些新的行为实验证明了这一点。
In a task where subjects had to grasp wet marbles and move them through a hole and out the other side,
在一项研究中，受试者必须抓取湿的大理石，并将其扔到洞的另一端，
those with pruney fingers finished the task significantly faster than those with smooth fingers.
手指有皱褶的受试者，明显比手指光滑的受试者更快完成任务。
Pruney fingers not only ought to enhance grip in wet conditions but do.
手指皱褶不只是“应该会”在潮湿情况增加抓取能力，而是“确实会”。
So, pruney fingers may be a crucial part of the primate repertoire.
所以，手指皱褶是灵长类的一项重要生物特征。
Maybe, once primates lost their claws in favor of fingernails,
也许，在灵长类选择指甲而失去尖爪的时候，
rain treads were needed to deal with the especially challenging, often wet, grip-heavy forest habitats.
这些凹槽就派上用场，来应付这具挑战性、时常潮湿又十分仰赖抓取力的森林栖息地。
By looking closely at the mysteries in our world and trying to find things that look similar,
通过深入了解我们世界的奥秘并试着找寻类似的模式，
like our wet fingers and rain treads, we can come up with ideas about what's happening.
比如说泡水的手指和轮胎凹槽，我们就可以对发生的现象提出设想。
And that's a good way to think about all sorts of questions in life, too.
而且，在面对生活中的各种问题时，这也是一种不错的思考方式。