Why pruney fingers

Sure enough, prune fingers were more efficient. Score one for Changizi. A big stumbling block, however, is that no one knows whether any animal—aside from humans and macaques—gets pruney fingers. Answers will have to come from more studies of how humans use their wrinkly fingers and toes. Changizi has the perfect subject group in mind: parkour athletes who freestyle run, roll, tumble and climb outside of gyms. Have you ever stayed in a pool or bathtub so long that your fingers got wrinkly?

This is normal — and can even affect your toes. But why does it happen? Even though you can't see it, your skin is covered with its own special oil called sebum say: SEE-bum. Sebum is found on the outermost layer of skin.

However, a similar 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. Likewise, a group of Taiwanese researchers conducted a series of experiments aided by a 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. The wrinkling of your skin is a perfectly natural reaction Credit: Getty Images.

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. The key is to assess the impact of wrinkled skin on locomotion, rather than on dexterity. His ideal experiment? Recruiting parkour experts to show off their urban acrobatics while either wrinkled or non-wrinkled, and in wet or dry conditions. Changizi thinks that the wrinkles act like rain treads on tyres.

They create 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.

Scientists have known since the mids that water wrinkles do not form if the nerves in a finger are severed, implying that they are controlled by the nervous system. In a study published online in the journal Brain, Behavior and Evolution , Changizi and his team studied photos of 28 wrinkled fingers 1. The team saw that all of them had the same pattern — long, unconnected channels branching from a point at the top of the finger.

When we press down with a finger, we apply pressure from the tip backwards. The sides of the finger are like cliffs where water can easily fall away, but the flat part is more like a plateau where water can pool.

Wrinkles form on the plateau because "that's where all the work has to be done to channel the water away", Changizi explains. Not everyone is gripped by the new theory. 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. But 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.