Why do fingers wrinkle in the water?

Well, an evolutionary neurobiologist seems to have found an answer for this. According to him, pruning fingers could be a survival mechanism, one that has evolved over thousands of years, for humans to grasp better in wet conditions.

Pruning fingers: an adaptive mechanism?

For many years, scientists have believed that 'pruning fingertips' is a result of water absorption, as our bodies are not designed to be immersed in water for long periods.

However, the present study rules out the previous belief and provides evidence that rather than being accidental, wet-induced wrinkles have been selected to enhance grip in wet conditions.

Lead researcher Mark Changizi, an evolutionary scientist at the 2AI Labs in Boise, Idaho, told Nature News, “Wrinkles act like rain tread on tyres by forming channels that allow water to drain away as we press our fingertips on to wet surfaces.

“This allows the fingers to make greater contact with a wet surface, giving them a better grip.”

Study details and findings

To test the hypothesis, Changizi and his colleagues looked at the photos of 28 wrinkled fingers from 13 hands. They noticed that all the fingers had the same pattern – long, unconnected channels branching from a point at the top of the finger.

“We began pilot experiments," said Changizi. “The results thus far suggest that, yes, being pruney helps.”

Scientists have known since 1930s that wet-induced wrinkles do not form if nerves of a finger are severed, suggesting that pruning of fingers is controlled by nervous system rather than outside factors.

“I stumbled upon these nearly century-old papers and they immediately suggested to me that pruney fingers are functional,” the Nature News quoted Changizi as saying.

“I discussed the mystery with my student Romann Weber, who said, "Could they be rain treads?" "Brilliant!" was my reply.”

The study titled “Are Wet-Induced Wrinkled Fingers Primate Rain Treads?” is published online in the journal 'Brain, Behavior and Evolution.'

Changizi further intends to explore the idea in animals who live in wetter habitats, and whether wrinkled fingers are superior to non-wrinkled fingers in wet conditions.

Study draws criticism

Though findings of the study appear convincing, not everyone is gripped by the new theory. “This hypothesis is unjustified,” says scientist Xi Chen of Columbia University in New York.

Chen claims that fingertips wrinkle because blood vessels constrict in hot water, causing the tissue beneath the skin to shrink.

However, Chen's theory holds true only for hot water and does not explain why pruning occurs in cold water.

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