冷知識 爲什麼洗澡時皮膚會變皺(下)
To see if wrinkled primate fingers had similar features to river basins, Changizi and his team analysed photos of 28 human fingers. They found that wrinkled fingers had the exact inverse formation as river drainages, with a raised, interconnected “tree” of bumpy skin, punctuated by diverging, disconnected sunken channels.
爲了確定靈長類手指起皺是否與江河流域有共同點，尚依茲和他的團隊分析了28個人類手指的照片。他們發現起皺的手指恰好是逆向的河流排水系統，鼓起的皮膚形成了凸起的相互連通的“樹狀”結構，而分叉的、互不連通的、下沉的渠道加強了這一結構。
The ridges aren’t haphazardly placed; that inverted pattern actually makes sense. Rivers combine water, while the channels on a wrinkled finger and meant to force water away. “The act of pressing a fingertip down on a wet surface squeezes the fluid out from under the finger through the channels, and upon completion of this single pulsatile flow the entire finger’s skin contacts the surface,” write the researchers.
凸起的紋路是有章可循的；逆向的結構是有根據的。儘管河流將水匯聚起來，但起皺的手指上的溝渠是以排水爲目的。“把指尖按壓在潮溼的表面上，手指上溝壑中的水就被擠出，完成這樣的一次脈動後，手指的皮膚就完全貼住表面了，”研究者寫道。
And then there’s this: wrinkles don’t appear until around five minutes of constant exposure to water, meaning that incidental contact isn’t enough to result in wrinkling, the response only becomes useful in rainy or dewy conditions. And it occurs far more quickly in response to freshwater than seawater, which could reflect the circumstances in which it may have originally evolved in primates.
另外，皺紋會在持續接觸水五分鐘後出現。也就是說，偶然碰到水並不足以導致皮膚起皺，這種反應只在有雨水或露水的環境下才會發揮作用。而在淡水中出現這一反應的速度比在海水中快很多，這說明這一反應可能原本就是靈長類進化的結果。
Even if the wet-wrinkling response didn’t explicitly evolve to aid in gripping, it could still be that it remains useful for the task. Indeed, a 2013 study conducted by British neuroscientists uncovered evidence that wrinkled fingers aided people in manipulating wet objects.
儘管沒有清晰的證據證明泡水起皺反應就是爲了增強抓握力而進化出來的，但是它仍然有利於人類完成這類任務。2013年英國神經科學家發現證據，證明起皺的手指有助於人操控潮溼的物體。
In the experiment, 20 people had to transfer 45 objects of different sizes – all marbles and fishing weights – from one container into another. In some cases, the objects were dry while the participants’ fingers were either smooth or wrinkled. In other cases, the objects were submerged. They found that wrinkled fingers allowed the participants to more quickly transfer the objects when submerged, though they made no difference for dry objects.
在實驗中，20個人將45個不同大小的物品——所有都是大理石和釣魚用的沉子——從一個容器取出，放到另一個容器中。一些情況下，物品是乾的，而被試者有的手指是平滑的，有的是起皺的。在另一些情況下，物品泡在水裏。他們發現，起皺的手指能讓被試者更快地搬運水中的物品，但是對乾的物品沒有作用。
However, a similar 2014 study conducted by German researchers found the opposite. In that study, the researchers had 40 people transfer 52 marbles and dice of different sizes and weights from one container into another. They found, however, no significant differences in the participants’ ability to manipulate the objects, no matter whether their fingers were smooth or wrinkled, and the objects dry or submerged.
不過，2014年德國研究者進行的一個類似的研究產生了相反的結論。在該研究中，研究者讓40個人在兩個容器之間搬運52枚不同大小的大理石和骰子。但是結果發現，不論手指是光滑的還是皺的，也不論物品是乾的或是溼的，被試者操控這些物品的能力都沒有變化。
Likewise, a group of Taiwanese researchers conducted a series of experiments aided by a 24-year-old male volunteer. They assessed the friction applied to a smooth surface by his smooth or wrinkled fingertips, for example, and how much force his hands applied when sliding across a bar. They also measured his ability to force two ends of a spring together. Rather than finding no differences, however, they actually found that wet-wrinkles resulted in decreased performance for each test.
臺灣的一些研究者也有類似的發現。在一名24歲男性志願者的幫助下，他們進行了一系列的實驗。比如，他們讓志願者用光滑或起皺的手指接觸一塊光滑的表面，根據他的手撫摸時的力量計算摩擦力。他們還測量了志願者擠壓彈簧兩端直到合攏的能力。然而，他們不僅沒有發現任何變化，還發現在每項測試中起皺手指的表現較差。
Of course, if the wet-wrinkling response did evolve as an adaptation, it was certainly not for the highly contrived laboratory conditions in which these experiments were run.
當然，假如泡水起皺反應真的是適應環境進化的結果，那它當然不適用於這些精心設計的實驗環境。
Changizi thinks that the wet-wrinkling response is useful for supporting one’s own body weight, not for fine-motor manipulations of small objects. “If you're really going to do a behavioural test where it matters, [it should be] gripping onto trees or heavier things, not little marbles,” he says. “You’re not at a risk of hydroplaning in any way,” he points out, when your task is to transfer marbles between buckets. The key is to assess the impact of wrinkled skin on locomotion, rather than on dexterity.
尚依茲認爲泡水起皺反應有利於支撐人體的重量，但不利於對小物品的精細操作。“如果你真的打算進行行爲測試，那應該測試抓住樹枝或其他較重的東西，而不是小塊的大理石。”他說。當說到把小塊大理石從一個水桶搬到另一個水桶時，他說：“無論如何，你沒有輪胎打滑那樣的風險。”關鍵是評估皮膚起皺對運動的作用，而不是對靈敏度的作用。
His ideal experiment? Recruiting parkour experts to show off their urban acrobatics while either wrinkled or non-wrinkled, and in wet or dry conditions. “In some kind of safe way,” he adds.
他理想的實驗是什麼？招募跑酷達人，在潮溼和乾燥的時候和在皮膚起皺和不起皺的情況下，展現他們在城市中的雜技。“以某種安全的形式。”他補充道。
