Why Do We Have Fingerprints? | Hacker News Reader

Why Do We Have Fingerprints?

newscientist.com

19 pointsmhb29 comments

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.

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.

For heavy objects, it's probably not so relevant.

But in my experience, more friction would probably be useful when holding tools/weapons. Hammers have a rubber grip, for example. I've noticed I lose smooth eskrima sticks far more often than ones I've taped. In an natural selection event, that could be lethal [1].

[1] http://www.youtube.com/watch?v=c_qwaXb6kAE

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.

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.

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.

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.

Tire treads?

Tire treads are mostly to prevent hydroplaning.

(Bicycle tires can't hydroplane, at least not at bicycle speed, and therefore road bike tires don't have treads. Treads reduce the contact area between the tire and the road, resulting in worse traction than a perfectly smooth tire.)

Hmmm, so do fingerprints prevent hydroplaning?

I have never noticed my fingers hydroplaning, so apparently yes. Mystery solved!

The earlier example of grasping a wet wine glass. That would seem to be an example.

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.

I guess the blind spot on our retinas also must show the super intelligent attention to detail.

If there was a designer of the human, "intelligent" isn't the adjective I'd use-- it seems more hacked together than engineered....

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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.

“When you do things right, people won’t be sure you’ve done anything at all.”

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

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.

Straw man. Who just answers god did it?

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

It's how god brands his flock

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.

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

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.

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

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.

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.)

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

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