Human fingers go wrinkly in the bath to give us better grip in the wet, scientists have discovered, contradicting a widely held belief that osmosis is the cause.
Wet fingers and toes wrinkle after about five minutes in water but surgeons discovered nearly a century ago that cutting a certain finger nerve prevents wrinkling, suggesting that something other than osmosis was at work.
In a paper published in the journal Brain, Behaviour and Evolution, U.S. scientists report that “rather than being an accidental side effect of wetness, wet-induced wrinkles have been selected to enhance grip in wet conditions.”
The wrinkling creates a ‘tread’ similar to the tread on tyres designed for better road-grip under wet conditions, the paper said.
“We show that their morphology has the signature properties of drainage networks, enabling efficient removal of water from the gripped surface.”
In other words, the wrinkle patterns are designed to draw water away from the surface and improve grip.
“Moreover, of course, the fact that wet wrinkles happen nowhere else on the body except on the fingers and feet is consistent with this rain tread hypothesis,” the paper said.
Professor Maciej Henneberg, an expert in anthropological and comparative anatomy from the University of Adelaide and editor-in-chief of the Journal of Comparative Human Biology said wrinkling of fingers and toes is a human adaptation to life in water.
“Recently, various hypotheses relating human evolution to the life in water, mostly as wading or "grazing” in littoral areas, have been advanced by German, Belgian and Australian scholars,“ said Professor Henneberg, who was not involved in the finger wrinkle study.
"According to those hypotheses, our ancestors were what I call peri-aquatic – that is, spent a lot of time collecting foods along shores of seas, lakes and along riverbanks, often wading or immersing themselves partially in water. Littoral areas are rich in foods digestible for humans.”