15
Recent published papers suggest that finger-
wrinkling plays a role in assisting us with gripping
objects. Much like the texture of rain treads or tires,
the grooves resulting from immersed fingertips
provide better grip and higher friction in wet
conditions. The gaps act as drainage networks for
directing extra moisture away from the surface
[2]
.
To test this hypothesis, twenty participants in
the age range of 21 – 34 were asked to manipulate
a total of 45 objects from one container to another
with dry fingers, once with the objects submerged
and once when they were dr y. The subjects
were then asked to immerse their hands in 40 °C
tap water for 30 minutes and repeat the object
transfer experiment in both scenarios. In each
case, scientists measured and compared the time
it took to transfer all objects. The results showed
that moisture-induced wrinkled fingers were more
efficient in transferring submerged objects than
fingers that were not soaked. However, there was
no difference in transfer time in manipulating dry
objects with or without wrinkled fingers
[3]
.
The results certainly support the theory that
wrinkled fingers provide better grip. Practically,
perhaps this provided our ancestors with an
easier time gathering or collecting food in rivers
or in wet weather. Similarly, wrinkled toes may
have been able to provide superior footing for
our ancestors during wet conditions. While this
speculation seems to help explain the peculiar
biological reaction, it does not address why digits
are not constantly wrinkled. It is postulated that
individuals having wrinkled fingers will result in a
reduction in fingertip sensitivity and an increase
in skin vulnerability. Thus, wrinkled fingers are
not evolutionarily preserved because the risks of
having this feature cannot outweigh its benefits
under dry conditions
[3]
.
夏
日炎炎，最涼快的活動當然是暢泳一番。泡水半
小時後，大家也許會發現手指頭和腳趾都起了皺，這種情
況在平常洗澡時也會發生。同學們有沒有想過其中的原
因和背後的生物意義？
曾經有學者提出手指頭和腳趾起皺，是皮膚表層（稱
為角質層）滲透膨脹的結果。顧名思義，滲透作用就是水
分會透過細胞膜，從低濃度溶液滲入到高濃度的一方。然
而有證據顯示手指頭沒有神經的部分是不會起皺
[1-2]
，同
樣情況可見於神經被切斷的個案
[3]
。
目前研究指出在冷潮濕情況下手指頭變皺是因為血
管收縮。這過程是由自主神經系統控制，部份外圍神經系
統亦參與調控其他重要的功能，例如心跳、消化系統、呼
吸系統等等。因此，手指頭的體積會減小，引致手指頭和
腳趾出現脊形圖案
[3]
。可是，手指浸泡在溫水中並不會令
到血管收縮，但手指仍然起皺。這個奧妙的機制有什麼生
物作用呢？
近期幾份研究論文指出人類手指、腳趾泡水後會起
皺，是讓我們在水裏更容易抓緊物件。手指頭浸水後出現
的坑紋就像雨胎的表面，可以在潮濕情況下提供更好的
抓力和摩擦力，當中的槽就像去水的管道一般，將多餘水
分導走
[2]
。
為了驗證這一假設，科學家邀請了二十位年齡約21
－34歲的參加者，用乾燥的手指拿起45件物體，從一個
器皿送到另一個。其中一次物件是浸泡在水中，另一次物
件是乾燥的。之後，參加者把手指浸泡在40℃的自來水
30分鐘，然後重複實驗。每次實驗後，科學家測量和比較
傳送物件所花的時間。結果顯示，起皺的手指移動潮濕物
件，要比乾燥手指更有效率，但在乾燥的環境中，手指是
否起皺對傳送時間沒有明顯影響
[3]
。
實驗結果的確支持了上述的理論，手指起皺現象提供
了更好的抓力，可能讓我們的祖先較輕鬆地在河裏或是
潮濕的天氣中採集食物。同樣地，起皺的腳趾可以令他們
在潮濕的情況下更能抓緊地面。這套說法雖然可以解釋
這種特別的生理作用，但仍然不能解釋手指頭為何不會
老是皺起。可能是因為起皺會減弱手指頭的靈敏度和增
加皮膚的脆弱性，在乾燥環境下遇到的風險高於利益，所
以沒有在進化過程中被保留下來
[3]
。
References
[1] Yin, J., Gerling, G. J., Chen, X. (2010). Mechanical modeling of a wrinkled fingertip immersed in water. Acta Biomaterialia 6 1487-1496.
[2] Changizi, M., Weber R., Kotecha, R., Palazzo, J. (2010). Are wet-induced wrinkled fingers primate rain treads? Brain Behav Evol 77:286-
290. Retrieved from
[3] Kareklas, K., Nettle, D., Smulders, Tom V. (2013). Water-induced finger wrinkles improve handling of wet objects. PMC doi: 10.1098/
rsbl.2012.999
