h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Why does everyone have a unique fingerprint? I know they are classified as arches, whorls and loops, and that they are said to have evolved to help with gripping. But why all slightly unique? Are there other pattern features that are all unique such as the pattern of convolutions on the cerbral cortex of the brain?

Yes I know DNA patterns are unique, but that's because the genes get shuffled every time in reproduction, and occasionally chance mutations occur.

Isn't it true of most body-parts? The possible variations in shapes and size mean that no two ears are identical, for instance. The reason it's special with fingerprints is that they are often stamped on things at a crime scene, so their uniqueness has a very particular use.

Yep which goes to show that not all features convey a Darwinian advantage. On one level some things are always constant, eg all angiosperms, flowering plants, have flowers; all mammals have breasts for suckling but they can be all sorts of sizes and shapes.

I guess there's a fractal element to it. The basic rules could be set up the same in two different people's DNA, but the way a fingerprint is built from them is chaotic, so early little differences as we develop become important in determining the eventual pattern.

<<they can be all sorts of sizes and shapes.<<

and even can differ in number. Didn´t Ana Bolena have s?

and... what would say Darwin of this?

http://www.news.com.au/story/0,27574,25290859-36398,00.html

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That'd be great instead of fingerprinting they track you down by size.

I'm sure this is going to get d.

>they track you down by size.

The mind boggles at what sort of crime that might be relevant for.

>>and even can differ in number. Didn´t Ana Bolena have tit tit tit s?


And also Chandler from 'Friends'. He had an extra 'nubbin'. Very common, I believe. And as for myself...my little toes are rotated 90 deg outwards, so that their nails are on the sides of my feet.

Fingerprints aren't are only distinguishing characteristic, merely one that is (relatively) easily distinguishable*. Obviously we all differ in many respects. Another way to characterise individuals would be by collecting various 'anthropometric' data such as stature, arm length, head circumference, finger length...whatever...and compare them to population means. For example...many people are exactly average in height. Fewer people are exactly average in height and 75% average in head size...even fewer average in height, 75% average in head size and 67% average in finger length...and so on. It doesn't take that many dimensions to produce a 'signature' that is unique within the human population of 6 billion.


* We should be wary of fingerprint data, though. There was a notorious recent case in which a Scottish police officer was wrongly convicted because her fingerprints, taken when she was guarding a murder scene, were judged to match those on the murder weapon. Similarly with DNA. All it does is narrow the odds that two samples aren't the same.

Suddenly remebered an old schoolboy joke:

Doctor: Do you mind if I weigh them?

>they track you down by size.<<

<<The mind boggles at what sort of crime that might be relevant for. <<

I´ve thought of a story for that.

The police find a man shocked, catatonic, lying on a bed with their arms lifted and their hands like clutches, like holding something.

After trying severals lines of investigation, they decide to follow an idea of a member of the Criminal Investigators.

His idea led them to compare the size of his three usual girlfriends.

Thinking more about this from the biological angle...(trying to distract my mind from thoughts of s ), I suppose some biological features only become strongly relavent over aeons of time and due to possible environmental factors, so certain characteristics are suddenly selected for. But clearly the finer points of some things are just fairly neutral .

Love your idea Mar. You must try to publish.

This thread could go off in so many directions, scientific, artistic and political.

Yes, this thread is getting effers-vecent.

Ed:
<<my little toes are rotated 90 deg outwards, so that their nails are on the sides of my feet.<<


How useful! to scracht I mean.
Those are like cock spurs, an evidence that there were cocks in your ancestors

So now we've had fingers, s and cocks

Looking at mine, finger prints that is, I have 4 arches, and 6 loops but no whorls I'm sad to say.

"Scottish police officer was wrongly convicted because her fingerprints...were judged to match those on the murder weapon. Similarly with DNA."

The problem in both cases is not the uniqueness of the fingerprint or the DNA but rather the limits in how we check for matches. In the fingerprint case the problem was that the match was only on 3 or 4 points (if memory serves) and it is quite possible that completely different fingerprints may match on a few points.

Similarly for DNA they don't check the whole thing but just a subset and yes it is pretty good at matching, and you get very high odds, but of course it could also match some other random persons and has a higher chance of matching with relatives. Which must make using DNA evidence rather difficult in the Fens

The fact that most people either don't know this or don;t consider it relevant has been used by lawyers to help their case and instances of jury members being dismissed in the states because they have an understanding of genetics and probability and DNA have occurred.

I don't know about cock fighting...but we bonobos famously engage in 'penis fencing'. http://en.wikipedia.org/wiki/Bonobo#Sexual_social_behavior

There are supposed to be so many possible variations of fingerprints, that no two people are likely to have the same. Even twins. I don´t believe this theory has ever been proven though. Ear prints are supposed to also be unique, but less likely to be left at a crime scene. Then there´s of course the koala bears.

indeed so, but they don;t match the whole fingerprint.
What they do is to note the position of certain features - where ridges join or seperate, mid point of the curves of whorls that sort of thing and then they check the position and relation of those points with other such mappings.

So although the whole fingerprint does seem to be unique, they don't check the whole fingerprint, just a subset of specific points. And they don't even need to match all of them, just a subset. This subset is not unique.