Forensic Science and Fingerprint Uniqueness: Investigating the Truth

[matthyaouw]

I often hear that fingerprints are unique, and you will share yours with no one. How much truth is there to this? I'll accept that there is very little chance you will find someone with identical finger prints, but I'm not entirely convinced that no two people will ever have identical ones. On what do forensic scientists base their claim?
Since criminal convictions can be made on only one fingerprint, or a fraction of a fingerprint in some cases, I also wonder what the chances are of sharing one fingerprint, of a fraction of one with another person.

 

[DocToxyn]

I found an interesting transcript that speaks to this and more regarding fingerprint indentification. Basically it comes down to the fact that no two indentical prints have ever been found, therefore the weight of evidence suggests that no two identical prints will ever be found. It does seem hard to accept that, when so many things in science we thought were true later turn out the be false, or at least not entirely true. However this quote from the article seems to answer this issue.

"The basis for individualization is that the friction ridge arrangement for each finger, palm, and foot is unique and permanent. Identification is a composite of several factors, each having a different relevance for each comparison conducted. The comparison process therefore is both qualitative and quantitative." And that is precisely what David Ashbaugh has been saying. That is what John Vanderkolk was saying here earlier today.

It goes on to say that there are four elements to identification criteria, and this first one I think is, well, I think I will let you make up your own mind, "There must be an agreement of fiction ridge formation. At a minimum, level one and level two detail must correlate. Level three detail can be used as necessary and is generally relied upon during the comparison process, but commonly not during the identification decision, unless the quantity of level two detail is minimal and the quality of level three detail provides sufficient clarity." That seems reasonable.

When it comes down to using fingerprints as part of the body of evidence in a crimimal case many characteristics are factored in, quality of print, how muh print is there, how many prints, level of detail, etc. This along with the mass of other evidence combines to prove innocence or guilt. I'm not all that familiar with case law but I think one needs a little more than simply a fingerprint to prove "beyond a reasonable doubt" that the accused is guilty.

 

[iggybaseball]

I wonder if expression of our genetics has anything to do with how our fingerprints form. Perhaps then fingerprints are unique. Otherwise it does seem like two individuals having the same fingerprint is just "improbable" not "impossible".

 

[honestrosewater]

I wonder if expression of our genetics has anything to do with how our fingerprints form. Perhaps then fingerprints are unique. Otherwise it does seem like two individuals having the same fingerprint is just "improbable" not "impossible".

I would guess that they are determined by genes, but so is eye, skin, and hair color, and those aren't unique.
There's some limit to what you can measure, and the size of the ridges and whole prints is limited, so there should be a finite number of possible fingerprints, right? Once you have more actual fingerprints than possible fingerprints, you'll get identical fingerprints (if this hasn't already happened by chance).

Edit: But considering how a print got wherever it is could make things better by establishing a shorter time frame. For instance, you probably wouldn't need to consider people who've been dead for over 200 years. So the number of actual prints wouldn't necessarily accumulate.

 

[selfAdjoint]

I would guess that they are determined by genes, but so is eye, skin, and hair color, and those aren't unique.
There's some limit to what you can measure, and the size of the ridges and whole prints is limited, so there should be a finite number of possible fingerprints, right? Once you have more actual fingerprints than possible fingerprints, you'll get identical fingerprints (if this hasn't already happened by chance).

But see this: https://www.physicsforums.com/showthread.php?t=83683

 

[LeonhardEuler]

I would guess that they are determined by genes, but so is eye, skin, and hair color, and those aren't unique.

Identical twins have different fingerprints and they have the exact same DNA, so fingerprints must not be determined by genes.

 

[honestrosewater]

Oh, right, "no two identical prints have ever been found". Thanks.

 

[matthyaouw]

http://www.livescience.com/othernews/050913_fingerprint_mistakes.html

I just stumbled across this.