Consider this: when human beings step out of the pool,
just two areas of their body wrinkle up, their fingers and their toes.
Consider further that scientists have little idea whether other mammals (save
for the macaques) experience this same phenomenon. What’s the purpose?
Years ago, it was believed that wrinkled fingers and toes
was caused by osmotic (think: osmosis) reactions. Two common theories were
advanced: 1. Fingers wrinkle because water enters the tip, and seeks to balance
the water content on both sides; and 2. Wrinkling is the result of water
passing into the outer layer of the skin and making it swell up. But in
the 1930s, researchers discovered that if you sever the nerves in your finger
(not recommended, by the way), the wrinkles won’t form.
The ready conclusion? Wrinkling is an involuntary
reaction by the body’s autonomic nervous system (the system that controls
breathing, heart rate and perspiration). Specifically, wrinkling is caused by
blood vessels constricting below the skin.
But why does it exist? What’s the evolutionary
purpose? Recently, neurobiologist Mark Changizi and colleagues developed a
theory that wrinkling is designed to enhance human grip, and last year an
independent research team out of the UK’s Newcastle University confirmed his
hypothesis. They found that, like rain treads on tires, pruney fingers
“create channels that let water drain away, allowing them to make better
contact with damp surfaces,” according to a piece authored by Ed Yong, for
National Geographic’s Phenomena.
Becky Summers, author of an article written for Nature
magazine, quoted Tom Smulders, an evolutionary biologist at Newcastle
University, UK, and a co-author of the paper. Said Smulders: “We have shown
that wrinkled fingers give a better grip in wet conditions — it could be
working like treads on your car tires, which allow more of the tire to be in
contact with the road and gives you a better grip.” Summers, paraphrasing
Smulders, explains that “wrinkled fingers could have helped our ancestors to
gather food from wet vegetation or streams.” The analogous effect in the toes,
the article adds, could help us to get a better footing in the rain.
Summers goes on:
“Given that wrinkles confer an
advantage with wet objects but apparently no disadvantage with dry ones, it's
not clear why our fingers are not permanently wrinkled, says Smulders. But he
has some ideas. ‘Our initial thoughts are that this could diminish the
sensitivity in our fingertips or could increase the risk of damage through
catching on objects.’”
Some take issue with Changizi’s evolutionary
hypothesis, raising the concern that testing human beings in their current
form won’t necessarily help us explain evolutionary origins. Said Yong, in his
piece for Phenomena: “The new study . . . raises some interesting questions
about how to test evolutionary explanations. So far, all of the evidence for
Changizi’s idea comes from looking at modern human fingers. . . . If modern
human fingers grip wet marbles well, and form patterns that resemble rain
treads, does that tell us anything about the origins of such patterns or are
all such explanations merely just-so-stories?”
Steve Ferber is author of “21 Rules to Live By,”
available either at Amazon.com or Island Expressions, located on Daniel Island.
Reviews at www.21rules.com.
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