
Why Do We Have Fingerprints? - mhb
http://www.newscientist.com/article/dn17300-get-a-grip-truth-about-fingerprints-revealed.html
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wglb
So it seems to me that friction is a pretty dicey thing to measure. It seems
that friction is really a property of each of the two surfaces. For example,
if we are measuring the friction between fingers and a smooth surface, you
would notice that fingerprints reduce the friction. But what about the hand
gripping a tree branch? Might not the friction be increased in that sort of
surface-to-surface contact? Or hanging onto a hunk of the fur of a running
buffalo for dear life?

Their approach seems to imply relatively smooth surfaces: "Because there are
all the gaps between the fingerprints, what they do is reduce the contact area
with the surface"

I am not seeing any reference to the fractal nature of surface-to-surface
contact here.

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Retric
Also grip tends to have little to do with friction. When moving heavy objects
you curl your fingers around it vs. laying your hand flat and trusting in
friction. If anything reducing friction might be a good idea because you can
better position your hands for optimum grip.

Edit: When you move a couch you curl you fingers under an edge, hold onto a
tree branch you curl your fingers around it etc. Climbing a tree can involve
friction but usually it’s griping the texture of the bark.

PS: Consider how you would hold a wet wine glass.

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scott_s
I have to disagree based on my weightlifting experience. When deadlifting
heavy weight (1.5x bodyweight and higher), friction makes a big impact on my
grip. Sweaty hands, and even a bar with worn-down grooves, can significantly
degrade my grip. This is why weightlifters (and gymnasts) use chalk.

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Retric
Chalk does not maximize friction in all cases. With light pressure chalk
reduces friction, under heavy pressure it increases it. Which is clearly a
best case situation.

As an example of this pool players use chalk to smoooth out their stroke.

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scott_s
I don't think that's a function of pressure, but amount. If my hands were
caked in chalk, I probably would have a harder time maintaining grip. But if I
have just enough to maintain dry hands, but not enough to reduce friction,
then it helps.

~~~
Retric
No, damp hands stick to the pool que. But a vary light amount of chalk fixes
that problem. Friction is actually a fairly complex activity where you can
change both the contact friction and the rate of friction increase under
pressure in different directions.

You can slip on a vary thin layer of spilled sand, but trains use it to
increase friction between the wheels and the smooth track.

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ComputerGuru
Intelligent design proponents typically point at the fingerprint as something
evolution doesn't well explain and proof of ID. The Muslim's Quran speaks of
the fingerprint as a miracle of God's creation, pointing out the attention to
the finest details as proof of God's capabilities.

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dinkumthinkum
That doesn't really make sense though. Strictly speaking, evolutionary theory
and natural selection, etc describe a theory about a process. I don't think
the veracity of evolutionary theory or the explanatory power of it is
contingent on how well proponents of it can evaluate the specific "uses" of
adapatations.

ID is such a reactionary and contentless view that I find them actually far
sillier than outright creationists like Kent Hovind; at least they are honest.

~~~
username
ID is a "contentless view" as evolutionary theory is since some of the views
of ID are negations of views of evolutionary theory.

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biohacker42
_contentless_ is an excellent description.

Evolutionary theory implies many things. Like given these bones here, and
these other bones over there, we can expect a transition fossil between bones
X and Y to be found in soil layers roughly corresponding to time T.

ID implies that, nu-uh, it's god that did it.

That's not a contradiction, it's just answering _god did it_ to everything.

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username
Straw man. Who just answers _god did it_?

Reply: <http://www.uncommondescent.com/faq/#Godgaps>

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aptimpropriety
My initial reaction was to think about dealing with dirt. Ever try to maintain
grip on a very smooth surface covered with a thin layer of dirt/dust?

On fingers, this stuff slides into the 'crevasses' of the print. Extremely
pseudo-science, but in my 2 minutes of thinking seems like it could be worth a
thought. I'm sure those scientists used clean hands on their testing papers.

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dinkumthinkum
There's no reason to think that all adaptations are beneficial. Interesting
though.

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scott_s
Adaptations are, by definition, beneficial. There will be evolutionary by-
products, though; things that arise because of evolution, but there was no
actual selection pressure for them. Some changes occur because of genetic
drift, and others will be related to something else which was selected for.

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michael_dorfman
OK, let's rephrase, then: there's no reason to think that fingerprints are an
adaptation.

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scott_s
You mean there's not enough evidence either way. Which is why it's useful to
investigate if fingerprints do have a benefit. If they do, then that's a
compelling reason that they are an adaptation.

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jpwagner
Evolution suggests that convergence occurs with the best adaptation.

If you take for granted that striated prints are better than smooth ones, it
seems obvious that fingerprints would be nearly random striations because
converging the design has no benefit (ie randomness is the norm, not
convergence.)

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sp332
They're for sensing textures and other vibration filtering:
<http://www.sciencemag.org/cgi/content/abstract/323/5920/1503> ( DOI
10.1126/science.1166467 )

