

Theory suggests wrinkling of wet digits evolved for a reason - pixdamix
http://www.nature.com/news/2011/110628/full/news.2011.388.html

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pittsburgh
_Not everyone is gripped by the new theory. "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," he says._

Ugh. Explaining the mechanism behind a behavior is not an argument against its
purpose!

Scientist A: I think polar bears evolved white fur so they'd be camouflaged in
the snow.

Scientist Crazy Pants: No silly, polar bears have white fur because their hair
follicles contain keratin and are hollow.

Scientist A: I'm going to kill you.

~~~
flashingleds
I completely see your point, and in many cases I agree with you. But there is
sometimes a tendency for evolutionary biologists to assign deeper reasons to
things that are just a consequence of physics. Occam's razor and all that.

In this particular case that fact that the phenomenon is not present when the
nerves are severed does present a pretty relevant argument against simple
biomechanics.

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hugh3
Surely if it were that, then fingers should wrinkle faster?

If I stick my hand in water then it gets wet immediately, but doesn't wrinkle
for... what, fifteen minutes? And that's warm water -- cold water (like
practically all the naturally-occurring water in the world) takes a lot
longer.

And then, I can dry my fingers much faster than I can un-wrinkle 'em. Surely
the circumstances in which an ancestral human would:

a) Spend fifteen or twenty minutes in the water, then

b) Need to pick up something vitally life-preserving within the next few
seconds

would be sufficiently rare that it probably wouldn't have been a major
selection pressure?

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katovatzschyn
It doesn't seem like you understand how this would be a useful. This is not an
explanation for slipping in the water and wrinkling to climb back out, it's
for spending long periods, perhaps for fishing or during the wet season, and
still being able to grab and manipulate objects.

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bandushrew
Sorry, I am missing your point. In the absence of wrinkling, what is stopping
me from being able to grab and manipulate objects?

I can do that _without_ wrinkling, even in water.

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ableal
_Scientists have known since the mid-1930s that water wrinkles do not form if
the nerves in a finger are severed, implying that they are controlled by the
nervous system._

That is the amazing part, if it's not a merely mechanical process. A bit
further down they mention poor circulation also impeding wrinkling, so it may
have something to do with control of capillary blood vessels.

~~~
Alex3917
Your hands also don't get wrinkled in water with the maximum possible amount
of salt dissolved in it, no matter how long you stay there. It seems like this
must somehow be important.

~~~
bh42222
I think that may well be purely mechanical or actually osmotic.

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ianterrell
Articles like this satisfy some tiny general interest ( _wrinkles! neat!_ )
but then squander any good will by predisposing the public to completely
misunderstand evolution.

The trait may stick around if it's useful, but it didn't evolve "for a
reason."

~~~
lutorm
I would argue that it (unlike all the other things that did not evolve) _did_
evolve for the reason that it was useful. It's not like all of a sudden there
was someone that had wrinkly fingers and that "stuck around because it was
useful". In all likelihood, there were many incremental changes that were
progressively selected for and the "reason" for that selection is that it was
useful.

It seems to me that it's perfectly acceptable language to say that a cause is
the "reason" for an effect, even if it's not possible to assign intent.

Your comment reminds me of Feynman responding to the question of why magnets
attract each other (<http://www.youtube.com/watch?v=wMFPe-DwULM>) which, while
inscrutable from a physical point of view, seems not to be a fruitful way of
approaching questions. There are always levels of deeper understanding, but
you have to take it one level at a time.

~~~
ianterrell
> _it's perfectly acceptable language to say that a cause is the "reason" for
> an effect, even if it's not possible to assign intent_

Sure, but that's not the case here. While existing traits are selected for
based on fitness (which has absolutely no meaning outside of environment,
another rant), _new_ traits (whether wrinkly fingers in one leap or in several
small ones) are evolved by chance.

Evolution has no intent, no direction. Each individual trait has no reason
other than, "Hey, I'll try this out!"

In a society where a good chunk doesn't even believe evolution is an accurate
model, I think it's helpful to be precise with the language to minimize
misunderstanding which further inhibits the idea's acceptance.

~~~
zem
the problem is, scientists find it very handy to talk in terms of directed
evolution simply because it tightens up the language and everyone knows what
it's shorthand for. (where by "everyone" i mean other scientists)

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mhb
When I grip something with wrinkled fingers, I get the impression that the
contact surface compresses and smooths out the wrinkles. So they don't act
like treads. If I grip a glass with wrinkled fingers and pour water over my
fingers, I would expect the water to go around the contact surface - not be
channeled through the finger wrinkles.

For this hypothesis to make more sense, I would expect to see "micro-wrinkles"
not the large compressible ones which I actually do.

~~~
sliverstorm
You're misunderstanding how tread works. It is active only as it is pressed
down; it allows water to rush away from under the contact patch more quickly
and easily as pressure begins to be applied. It does not actually increase
mechanical grip, and in fact serves no purpose once full contact is
established. So, it does not matter if the treads get flattened by full
pressure- it has already done its' job.

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jeggers5
That's really interesting. Never thought about why my fingers do that!

I think this hypotheses is a little silly though.

~~~
mooism2
You think the hypothesis is silly? Why?

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sonnekki
I don't think it's silly, but I do think that it will be extremely difficult
to test. People that have damaged nerve endings of the fingers probably are
not good grippers, even if their fingers are wet. The control and the feedback
is simply not there.

~~~
Sandman
_People that have damaged nerve endings of the fingers probably are not good
grippers, even if their fingers are wet_

I guess you actually meant "even if their fingers _aren't_ wet"? But why do
you think it would be extremely difficult to test this hypothesis? All that
would be needed is to get a large enough group of people and test their
gripping ability on the same surface when their fingers are wet and when they
aren't.

~~~
cschmidt
Well not exactly. I'd imagine that the wet surface will always have lower
gripping ability. You want to know if the wrinkled fingers have better grip on
a wet surface than unwrinkled fingers. You could wet the fingers and
immediately test the grip (before wrinkles form), and then soak them in water
until they wrinkle and do it again.

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joejohnson
I did not know you could spell tyre with a 'y'. Is Nature a British
publication?

~~~
sjmulder
Yup, that’s British spelling. That’s why the bicycle that got tired joke never
works on Facebook if you’re from there.

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scottshea
I wonder when my revulsion at touching paper or other skin with wrinkled
fingers came into play?

