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Some parts of human skin, better known as glabrous skin, have a unique response to water. Unlike the rest of the body, the skin of our fingers, palms, and toes, and soles wrinkles after becoming sufficiently wet. Five minutes or so will usually do the trick.
人体有些部位的皮肤（通常指无毛皮肤）对水有特别的反应。手指、手掌、脚趾和脚底在充分润湿后会变皱，而其他部分的皮肤不会。浸水五分钟左右就会出现这种现象。
But why do these patches of skin wrinkle? Some think that this is a biochemical reaction, an osmotic process in which water yanks a handful of compounds out of the skin, leaving an expanse of parched, pruney skin in their place.
但是，为什么这些部分的皮肤会变皱？一些人认为这是生物化学反应，在渗透作用下，水吸走了皮肤中的一些化合物，导致皮肤干瘪，出现褶皱。
But a century ago, scientists already knew that this curious reaction wasn’t a simple reflex or the result of osmosis.
但是一个世纪前，科学家就已经知晓，这种奇怪的反应并不单纯是一种条件反射或渗透作用的结果。
That’s because surgeons learned that if certain nerves to the fingers were cut, the wrinkling response would disappear. Wrinkled fingers, then, are signs of an intact nervous system. Indeed, the wrinkling response has been suggested as a means of determining whether the sympathetic nervous system is functional in patients that are otherwise unresponsive.
原因是，外科医生发现，假如切除某些通向手指的神经，泡水起皱反应就会消失。由此看来，手指变皱是神经系统完整的标志。的确，一直以来，起皱反应都被用来判断患者的交感神经系统运作是否正常。
On all of this, the scientific community has consensus. But whether and how the wet-wrinkling response may have evolved, and if it even represents an adaptation in the first place, remains a contentious debate.
科学界已经对以上这些达成了共识。但是关于泡水起皱反应是否是进化得到的，是如何进化来的，以及它首先是否代表了对环境的适应，仍存在争议。
Neurobiologist Mark Changizi of 2AI Labs thinks it’s got to be an adaptation. Consider tyre treads. In dry conditions, smooth tyres can best maintain their grip on the asphalt, which explains why race cars typically have smooth, featureless tires. But when driving in rain, treads are far safer.
2AI Labs的神经生物学家马克•尚依兹(Mark Changizi)认为，这一定是一种适应。以轮胎胎面为例。在干燥的环境下，平滑的轮胎在沥青路面上的抓地力最好，所以赛车通常使用平滑、无特征的轮胎。而在下雨的环境下，带纹路的胎面的轮胎安全性更好。
Wrinkled fingers, then, could be optimally designed for gripping in both wet and dry conditions. It’s extremely difficult to prove that any biological feature is an adaptation, let alone why it may have evolved. But researchers can look for hints, tell-tale clues that indicate that a feature may indeed have evolved as an adaptation.
由此可见，手指变皱可能是为了在干湿两种环境下都能抓握而优化的设计。但是，要想证明某种生物特征是适应环境的结果是极其困难的，更不用说要弄清进化的原因了。不过研究者还是可以寻找蛛丝马迹，证明一种生物特征是适应环境的结果。
In 2011, Changizi and his colleagues found evidence that wrinkled fingers indeed act as rain treads, channelling water away from the fingers and toes during wet conditions, allowing primates – humans and macaques, to be specific – to maintain tighter grips.
2011年，尚依兹和他的同事们发现证据证明手指变皱确实和雨天使用带纹路胎面的原理一样。在潮湿的环境下，手指和脚趾的沟壑能够引导水流，让灵长类动物——具体来说是人类和猕猴——保持更强的抓握力。
In other words, the wrinkles that result from exposure to water can be thought of as tiny, manual river drainage systems. In a typical ‘watershed’, multiple streams combine into larger channels, which eventually dump into a central river, much like twigs combine to form branches, which flow into a tree’s trunk. The pieces of land between the streams and brooks, on the other hand, are disconnected.
换句话说，接触水所带来的皱纹可以被视作一套微型的人工排水系统。在一个典型的“分水岭”上，多条溪流汇聚成较大的河流，最后汇入中央河流，就好像树木的枝条汇合成枝干，最后汇合成树干。而从另一个角度来看，溪流之间的小块土地就被分离开来。
