I had never thought why it is only our fingers are toes thant wrinkle when they are wet for a long time. The reponse does not happen when the nerves are severed.
Mark Changizi et al. suggest that it is to enhance grip. See Are Wet-Induced Wrinkled Fingers Primate Rain Treads?
Mark Changizi, Romann Weber, Ritesh Kotecha, Joseph Palazzo. Brain Behav Evol (DOI: 10.1159/000328223)
Wet fingers and toes eventually wrinkle, and this is commonly attributed by lay opinion to local osmotic reactions. However, nearly a century ago surgeons observed that no wrinkling occurs if a nerve to the finger has been cut. Here we provide evidence that, rather than being an accidental side effect of wetness, wet-induced wrinkles have been selected to enhance grip in wet conditions. We show that their morphology has the signature properties of drainage networks, enabling efficient removal of water from the gripped surface.
There is some dispute on this interpretation – Ed Yong in Nature News: (June 28 2011) notes:
- “This hypothesis is unjustified,” says Xi Chen, a biomechanical engineer at Columbia University in New York. Chen thinks that the wrinkles have a simpler cause: when fingers are immersed in hot water, the blood vessels tighten and the tissue shrinks relative to the overlying skin. This contraction causes the skin to buckle. “It’s a classic mechanics problem,”
- neurosurgeon Ching-Hua Hsieh of the Chang Gung Memorial Hospital in Kaohsiung, Taiwan, says that the process Chen describes does not account for the fact that fingers wrinkle even in cold water, or that they do not wrinkle when their blood supply is cut off. He thinks people should be looking for more explanations of water wrinkling
- Changizi now wants to see if mammals that live in wet habitats are more likely to develop wrinkled fingers. “E-mails to a couple dozen primate labs led to a couple dozen ‘gosh-I-don’t-knows’,” he says. “It occurred to me to look at the bathing [Japanese] macaques, and I finally found one photograph [of a monkey] with pruney fingers. So it’s at least us and macaques, and surely many others.”
- The ultimate test of the hypothesis will be to see if people with wrinkled fingers are better at gripping in wet conditions. “We began pilot experiments,” says Changizi. “The results thus far suggest that, yes, being pruney helps.”
The findings could be important in OH&S where wet work is common and wrinking does not appear to have been taken into account in assessing grip. There could be a balance between a safer grip with wrinkled fingers and dermatitis from wet work. Perhaps there is even a case for bare feet with some wet work?
Wet work has been topical with many organsiations, eg
- EU-OSHA
- HSE UK (2010)
- Safework Western Australia (2006)
