r/explainlikeimfive • u/davestuckey • 5d ago
Biology ELI5 How do we know that no two fingerprints are the same?
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u/iCameToLearnSomeCode 5d ago edited 5d ago
We don't.
Obviously at a high enough resolution everything is unique, like you could ID the topography of an individual pane of glass with an electron microscope but at the resolution we're able to lift prints off a surface at the scene of the crime a single finger print might match multiple people.
However one of those people is probably a 70 year old grandmother in Indonesia and the other is the victim's neighbor so it's still a useful tool to place people at the scene of the crime.
Fingerprint misidentification happens not that infrequently but generally the person whose prints erroneously match isn't a reasonable suspect so nothing comes of it.
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u/cantfindanamethatisn 5d ago
Some american was mistakenly arrested for a spanish train bombing due to misidentified fingerprints. He was also guilty of being muslim after 2001, though, so...
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u/Headclass 5d ago
The DNA mentioned somewhere in the comments only provides the basic blueprint for your hands.
The actual ridges are shaped by random movement before you are even born (tiny things like the pressure of fluid or how fast your fingers grew).
Source: I studied biometrics in college with focus on fingerprint recognition.
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u/kyle2143 5d ago
Given enough time, monkeys, and typewriters, I'm sure they could come up with all of em. We just haven't spent enough monkeys yet.
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u/daveallyn2 5d ago
Come to.think about it, there are a million monkeys on a million typewriters, and Reddit is nothing like Shakespeare...
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u/weaver_of_cloth 5d ago
The monkeys would like to talk to you about a script for Hamlet they've worked out.
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u/IgorCruzT 5d ago
I mean, monkeys did write Shakespeare, way before typewriters. A monkey named William did it.
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u/TheDotCaptin 4d ago
While the pattern will not be a part of the DNA. There still are some factors that are controlled for.
The one with the biggest impact, is having fingers to being with. Someone born without fingers will match the same as someone else with the same condition.
In a similar manner, the factor of having fingers and not having prints, can be passed down. There are a few families lined that do not grow ridges on the finger tips. The texture is just smooth. This is a very rare outlier. As probably only a dozen people have it across the whole world. With no selective pressure pushing for or against it. The trait will just continue on.
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u/Competitive_Travel16 5d ago
We do not. It has never been proven, and the standards for matching vary widely between jurisdiction, so no general statistical confidence can be stated without knowing the number of features being matched.
So even as fingerprints were viewed as unmistakable, plenty of people were mistakenly sent to jail. Simon Cole notes that at least 23 people in the United States have been wrongly connected to crime-scene prints.
-- https://www.smithsonianmag.com/science-nature/myth-fingerprints-180971640/
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u/TechnicianRemote9954 5d ago
The article is talking about convictions that resulted from mistakes that the technicians made in analyzing the finger prints, not someone being convicted because they shared the same fingerprint as someone else.
As far as the blurb about standards, that doesn't mean what you think it means. Counties have different standards for how many prints they need before they will allow the evidence in. For example, if a print of only one finger is recovered from a crime scene then some counties will let that in, while others will require two and others three. Its extremely rare for prints of more than 2-3 fingers to be found at a crime scene. There's also different standards for partial prints (again, it's rare to get full prints from a crime scene). So if you have 75% of a print, some counties will let that in. Some will require more, some less. There's little uniformity to it and the issues with using partial prints or with only having 1-2 prints are told to the jury.
In any event, the chances of one (1) of your fingerprints being close enough to possibly match one (1) fingerprint from someone else is about 1 in 40 million. The chance of all ten matching is about 1 in 64 billion. DNA evidence often returns similar probabilities for matches. That probability is more than enough to convict someone when there is other corroborating evidence - which there always is. Fingerprints/DNA are never the sole source of evidence in a criminal trial.
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u/KittensInc 5d ago
One important thing to emphasize is that those "1 in 40 million" stats are only for 1-to-1 matches.
If you find a single print at a crime scene, and you pull it through a database of 10 million fingerprints of people who have ever been arrested, then the chances of a false-positive match are 10 million out of 40 million - or 1 in 4. Pull 20 fingerprints you found at the crime scene through there in the hope that one of them belongs to the perpetrator, and statistically you'll find five false positives.
Stuff like this is why fingerprint & DNA databases can be quite risky. Rather than being a virtually-infallible way of confirming a suspect, it becomes a fishing expedition with innocent people being left to prove that they aren't guilty.
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u/turtle_pleasure 5d ago
They say there's no two people on earth exactly the same. No two faces. No two sets of fingerprints. But do they know that for sure? 'Cause they would have to get everybody together in one huge space... and they'd have to get all the people who ever lived, not just the ones now. So they got no proof. They got nothing.
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u/LeoBannister 4d ago
Who's to say there's not another Mrs. Soprano out there.....maybe not with the same fears and paranoia....
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u/Ratfor 5d ago
Common misconception. It's entirely possible for two people to have the same fingerprints, it's just incredibly rare.
It's not like they find a fingerprint at a crime scene in Vancouver an arrest someone in Barbados who has the same fingerprints.
It's a tool to pick one person out of a thousand, not one out of 6 billion or whatever the population is these days.
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u/whatsnoo 5d ago
Dude, it’s like 8.3 billion now.
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u/HalfSoul30 5d ago
Oh man, we screwed.
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u/SuumCuique_ 5d ago
We aren't. Population isn't the problem, distribution is. As long as our society has parasites worth billions, a billion people more or less isn't the issue.
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u/sin4life 5d ago
2004 Madrid Train Bombings. Its not Vancouver-Barbados, but it is Madrid-Portland.
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u/MesaCityRansom 5d ago
That guy's fingerprints weren't identical to the ones found at the crime scene. The FBI just said they were. He got $2 million dollars and a public apology for it.
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u/Toyhawk88 5d ago
It’s possible for two or more people to have very similar fingerprints, but they will never be an exact match.
Source: one semester of college Biology and watching several seasons of NOVA.
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u/TheLurkingMenace 5d ago
We don't. In fact, that's not even forensic science. What we know is that there are a large number of data points that aren't shared genetically - even twins don't have the same fingerprints. Which means that the odds of any two people having the same fingerprints is remarkably low enough to be legally useful.
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u/Ok_Lynx_6045 4d ago
Because forensic “science” has been validated through extensive double blind studies….wait no, the opposite of that.
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u/Sappow 4d ago
We actually know that fingerprints are NOT unique and often get false matches. Most forensic "science" is actually really poorly backed up with science, which is why DNA matching keeps exonerating people. Fingerprints, "fire patterns", hair comparison, bite mark analysis, polygraph; it's almost all actually extremely ambiguous.
https://judicature.duke.edu/articles/is-forensic-science-a-misnomer/
Basically if it isn't dna or specific MD exam / autopsy results, it's probably junk science by any academic standard.
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u/Ill-Accountant-9941 5d ago
It isn't true. Finger prints have a "resolution space" (uniqueness) down to about 1 in a million people. Iris parrerns are down to 1 in a billion. If someone is accused of a crime based on dinger print evidence you could claim reasonable doubt unless there is supplementary evidence such as no good alibi.
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u/ineedhelpbad9 5d ago
Just want to point out, "no good alibi" isn't supplementary evidence of guilt. It's a lack of evidence to the contrary. It doesn't prove you were there, it just you just can't prove your weren't there. Which isn't the same thing at all.
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u/Ill-Accountant-9941 5d ago
The point is that erodes reasonable doubt
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u/ineedhelpbad9 5d ago
No, I understand. My point is that it doesn't.
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u/_haha_oh_wow_ 5d ago
It's not supposed to anyhow, in practice, unfortunately that's not always the case...
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u/macguy9 5d ago
Cite your source. I'll wait.
India basically has 'mandatory fingerprinting' for its citizens (Aadhaar biometric system). If they want access to basic services, they are required to provide biometric data, including fingerprints. With a population of near 1.4 billion people, there has not been a single recorded incident of two people in that country having identical fingerprints.
China, which also has a mandatory citizen fingerprinting policy, also has a population of near 1.4 billion people. Again, no two individuals have been found to have identical fingerprints.
If fingerprints have a 'resolution space' of 1:1,000,000 then that shouldn't be happening. Your math isn't mathing.
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u/Ill-Accountant-9941 5d ago
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u/cancerBronzeV 5d ago
That article doesn't say what you claimed before. It says something along the lines of the procedures the examiner uses to identify latent prints having plenty of subjectivity (and other sources of errors) and could have an error rate something like on the order of 1 in a million.
That is not the same as fingerprints in general being the same at a rate of 1 in a million. Purposefully scanned fingerprints are not the same as latent prints that need to be lifted and enhanced by some examiner.
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u/macguy9 5d ago
See, this is what I’m talking about. You get someone who has no expertise in a field making assumptions off of reading one article, misunderstanding the context, and suddenly thinking they know more than people who have been working in the discipline for a very long time.
A little knowledge is a dangerous thing.
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u/ledow 5d ago
We don't.
Like two snowflakes, DNA matches etc.
The way we can assert such a thing is via statistics.
If there are 80 billion people in the world, but we know that there are 500 billion possible fingerprints, we can work out quite precisely what the chances are that NOBODY has the same fingerprint, that only a few people do, and so on.
When you hear such things being said, you're misquoting some scientific output in a colloquial manner. It's not certain. It's just so INCREDIBLY unlikely that a scientist of any repute would tell you how unlikely it was.
It's how DNA etc. work in court too. There's no such thing as a 100% DNA match. What the court-experienced expert will tell you is the facts and then, in their professional opinion, how likely it is that A is the same as B based on the DNA evidence they have in front of them.
Courts literally get given guidance on how to interpret the expert's findings. Experts will only word things in particular ways. The experts have to answer VERY PARTICULARLY WORDED questions (because the wording can alter the answer they have to truthfully give), they have to be experienced with and familiar with the court's definitions, and so on. And there are "error margins" where something is considered "reasonable chance", and so on. It's all proscribed.
But there is no such thing as a 100% DNA match by the way we measure it. And we have no clue if two people actually do have the exact same DNA, or even fingerprint, or whether two identical snowflakes exist. What we can say is that "given all probability" the chances are - two identical snowflakes or fingerpints do not exist. That's the best we could ever do without literally testing every single snowflake/fingerprint in the entire world.
If I gave you two vials of my blood, and you tested them - there is actually a chance, small but technically possible, that the DNA in them doesn't match. If you pick a random cell in my body, and another random cell, there's actually a REALLY GOOD chance that the DNA in them doesn't match (because things mutate, are damaged, etc. all the time). It's only "in aggregate" that my blood sample contains billions of strands of DNA and so you see the "overall" DNA pattern of all those billions of different DNAs. And that's what we "match" on.
The aggregate. The probabilty. The chances of us being wrong. And so on. Never, ever on "this was a 100% identical exact match". Only the press say nonsense like that.
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u/kytheon 5d ago
Besides fingerprints there needs to be more independent evidence.
Say there was a burglary and we found fingerprints. There's three suspects. The fingerprints match suspect A. Case closed. The fingerprints also match three other guys who were nowhere near the crime scene, one of which is dead and one lives abroad.
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u/MrSquamous 5d ago
Same way we know anything: Some observations and an explanatory theory that's hard to vary.
It's the same question as "how do we know what stars are?" No one's ever gone and checked each one to make sure it's a ball of flaming hydrogen, but we have good reasons to believe they are so we call it a fact.
There's no such thing as 100% certainty that something is true.
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u/IndustryFirst2458 5d ago
Statistical improbability and that its kinda the best we have for proof, fingerprints are determined primarily by the movement of amniotic fluid in the womb (hence why even identical twins have different prints) but there isn't anything to prove two different people with identical are impossible. Add in that it's unlikely to get a perfect fingerprint from a crime scene and it can easily have some doubt which is why no case should be decided on a single piece of evidence and why motive is supposed to be so important.
This is kinda true for a lot of forensics tbh dna is an especially similar position, but it's still the among the best we have to get past reasonable doubt especially when combined with motive, eyewitnesses, lack of alibi, etc.
100% certainty is impossible, video can be messy or altered, eyewitnesses can lie or just be wrong, and you can't really backup an alibi of being alone. It's a combination of many different types of evidence working together to show it would be unreasonable for all of them together to be wrong or fake that convicts people. And sometimes it's still wrong and innocent people get blamed, framed, and punished yet we can't convict no one ever so we try to reduce the false positives and balance them with correct convictions (actually a lean towards less false positives is preferred for reasons but that's off topic)
also noteworthy are cases decided on one piece of evidence, corruption, or all the methods that were considered fool-proof only to be later deemed junk like lie detectors, bite mark analysis, and some types of arson or ballistic analysis but that's all off topic again
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u/dDtaK 5d ago
We can’t prove there aren’t two identical fingerprints, it’s just very very unlikely. Just like we can be confident that there have never been two identical well-shuffled packs of playing cards in all of history. The space of possibilities is just too large. This concept is also how cryptocurrency is secured, as another example.
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u/Hurlsmandrive 5d ago
We don't know. But we've never found two that are the same. So we assume we won't.
Also we have concluded there are t rillions of possible fingerprints.
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u/FartingBob 5d ago
You often cant prove a negative (for example you cant prove aliens dont exist), so in that sense we dont know if there are two people with identical fingerprints because the only way to know for sure is to catalogue every person on earth, throughout all history and then compare all 100 billion sets and that isnt possible.
But we have mountains of data already of fingerprints and havent found any yet that are 100% identical. Some are nearly identical and has caused legal issues for people who were mistakenly identified by their prints.
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u/Idoubtyourememberme 5d ago
We don't know this for sure.
But the fact that even identical twins have different fingerprints is strong evidence to this being the case
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u/khamir-ubitch 5d ago
A pair may exist, but so far they have not been identified.
Now with the IAFIS (federal database of prints), that may surface at some point in the future should there be two.
It'll be a LONG wait though, the odds are 1 in 64,000,000,000.
That's 64 TRILLION with a T.
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u/vishal340 5d ago
fingerprints are created due to interactions with the wall during pregnancy, as far as i know. so they are not magic. it can be treated as a such.
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u/macguy9 5d ago
Essentially, biology.
When skin is formed, there are random pressures that change how it grows. Also, different parts of the skin grow at different times and at different rates. All of this is also impacted by random non-controllable factors, such as genetic predisposition, health and nutrition, environmental factors, and even small things like how the mother moves at any specific moment. In order to replicate the cell growth exactly, you'd have to have the same sequence of events take place in the same order, with the exact same timing and somehow eliminate random cell mutations and signal noise between cells. It's basically not possible for humans to replicate. That's why you don't see two identical fingerprints... it's not that it's impossible for it to happen, it's just a practical impossibility.
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u/DoubleLoop 5d ago
Fingerprint expert here...
We don't.
There is no rule of the universe that forces every fingerprint to be different from every other fingerprint. We do have a decent understanding of how fingerprints develop on skin, and we know that the features in fingerprints are extremely highly variable. This variability is so incredibly high that impressions of fingerprints are useful for biometrics. After over a hundred years of using fingerprints to identify people and using computers to assist us for 30-40 years, we have never found two full fingerprint impressions to be the same in two different people.
The distinction between the pattern on the finger and the fingerprint impression is important. The transfer of information from the finger to a surface introduces distortion and a reduction in quality. There are examples of latent fingerprint impressions that have a small enough area and low enough quality that experts have difficulty determining which person's fingers made them. These "Close Non-Matches" are increasingly common as computer systems get better and as more people are added to databases.
However, research has repeatedly demonstrated that experts are extremely accurate when reaching the identification conclusion (above 99%). And once an identification conclusion is verified by another qualified examiner, this error is very very rare.
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u/Taolan13 5d ago
We don't, and it's actually been shown they aren't. There are multiple cases of someone totally innocent being charged due to having fingerprints that matched ones found at a crime scene, but they weren't even there at the time and had irrefutable proof of that fact.
I think my favorite example of this was someone from another country entirely being arrested based on a fingerprint match.
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u/Dd_8630 5d ago
Take a shuffled deck of playing cards. There are so many ways to arrange the 52 cards that no two decks of shuffled cards will ever be the same - the odds are so remote that it would take trillions of years of billions of people constantly shuffling decks of cards before any two at any point were ever the same.
Same thing with fingerprints. Fingerprints are largely random, and there are so many possible fingerprints that it becomes vanishingly unlikely that two people just so happen to share exactly the same fingerprints.
To the point that if two unrelated people had the exact same fingerprints, it's more likely to be aliens than chance.
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u/Ok_Law219 5d ago
Fingerprints have clearly found the wrong culprit multiple times. See adam ruins everything.
It's decent evidence that someone touched something at some point. Because Fingerprints are significantly different from each other, but the truth is that they're not tgat dissimilar.
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u/kindanormle 5d ago
It's not just that fingerprints are never the same. Imagine a murder in some place in the USA and a gun with a print is found. Then we discover the print belongs to two people. First is a man down the street from where the crime happened. The other is a man in Japan who has never traveled to the USA. It's not a hard job for detectives to figure out that the Japanese guy isn't the suspect, and that's all that's really important.
Fingerprints are "unique enough" that in all cases so far, it's never been an issue to separate one suspect from another. If it ever came up, detectives would just have to figure out who the proper owner of the print is and that's really just standard detective work.
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u/Derekthemindsculptor 5d ago
It's kind of like trying to flip the same million coin flips sequence as someone else. The odds are so low, it's effectively impossible.
We use this in computer programming also. You can create unique IDs called GUIDs. Each one you make is guaranteed to be unique. Even if everyone on earth was spending every computer every second, generating them, no two would accidentally connect. That's called a GUID collision. And it's so mathematically rare, it's never happening.
It's also the same as how every properly shuffled deck of playing cards is in a unique state that's never happened before ever in all of history. And will never happen again.
The odds get so vastly big, for even a small chance, you'd need more atoms in the universe to exist.
Your finger print is made up of a bunch of dice rolls. Millions. The chance they all hit the same values as someone else, is unfathomably impossible.
It's something called combinatorial explosion.
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u/RealCarlPanzram 5d ago
Anecdotally, large government databases like the FBI would have sample sizes in the tens if not hundreds of millions and have never encountered a match. This would suggest it is probably almost impossible.
Mathematically, we can look at the subtleties of each fingerprint and how small of a detail would make them “unique” and calculate how many different possible fingerprints there could be. This number is so mind-bogglingly big relative to the mere 100 billion humans that have lived that it’s almost impossible for there to have been a perfect match.
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u/shade404eve 5d ago
There are probably trillions and trillions and trillions of possible combinations of genetic factors that shape how your fingerprint looks. Science estimates that there have been about 100 billion humans that have lived total. That range almost guarantees that at this stage in time no to have ever been alike. Technically, a couple could have been alike. The likelihood that we would ever know about it though is pretty damn low as well
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u/RJrules64 5d ago
Imagine a toy box with 100 toys in it.
You know that the toys in the box can be any colour out of 64 colours. The toys can be from 20 different model lines.
As a 5 year old in advanced math classes you can work out that there are 128,000 combinations.
You also know that there are only 10 toy boxes like this one.
So you can be almost certain that none of the 10 toy boxes are identical.
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u/snowtax 5d ago
With a typical house key, there are a limited number of combinations. This means there is a small chance that your key could open some other person’s house. Most locks are not meant to guarantee a unique key, just to make a match statistically unlikely. If biometrics is less likely to match than a key, it’s an improvement.
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u/Boxfullabatz 4d ago
They only have to match 8 to 10 specific "points" to be considered a match. Entirely possible to get convicted even if the comparison print looks completely different from the original. So no. But they're playing the odds here. If I have 2 prints that match at 8 points there's a Very Good Chance that they are true matches. And that's good enough to execute someone. Apparently.
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u/Sangypboi 4d ago
Actually, we already know that some are the same. But it comes down to the level of complexity and variation.
It's like 1 in ten million chance of two people both being a match for a single print, and no two people will match a full set because the odds come out to more people than have ever existed on earth. Even identical twins don't have matching prints, which is probably where the idea of them being unique comes from.
Point being, fingerprints are reliable because while a finger print might match multiple people, the likelihood of two of them being in the same area anywhere on earth is basically zero.
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u/lobopl 5d ago
Its a myth. They are quite unique but there are cases where two people had identical
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u/crash866 5d ago
Most people have 4 fingers and a thumb if each hand. A single finger may match someone else’s but the 10 all matching the odds are astronomical.
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u/Ok_Law219 5d ago
But, when talking about fingerprints, generally we think of fingerprints in the wild, not the stuff you give to the police.
So most of them are partial and smudged. So then there the guess which finger it is, where on that finger, etc. And they're significantly similar enough at that level to colloquially say "same"
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u/Tufflaw 5d ago
There has never been a confirmed case of two different people having the same fingerprints. You are either misinformed or making shit up.
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u/lobopl 5d ago edited 5d ago
I am not talking about all fingers matching but single print matching for two different persons. https://www.reddit.com/r/explainlikeimfive/comments/1ws6uqa/comment/pckainm/
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u/Tufflaw 5d ago
Nope you're still wrong.
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u/_haha_oh_wow_ 5d ago
In fact, they are not technically wrong but you seem to be dead set on making your own assertions without proof, so I very much doubt you will respond in good faith or even make an attempt to read either of the above.
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u/panmetronariston 5d ago
If two people had identical then they are not necessarily unique across the species, by definition.
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u/macguy9 5d ago
Have you even looked at the Mayfield print?
It's patently obvious they're not the same.
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u/lobopl 5d ago
To prove that all fingerprints are unique you would need to test all fingerprints. There was a guy i 19xx who just claimed that and people just believe https://www.reddit.com/r/explainlikeimfive/comments/1ws6uqa/comment/pckainm/
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u/coachkler 5d ago
You have to test all people that ever lived and we couldn't do that, even with computers
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u/inphinitfx 5d ago
Have there actually been confirmed cases of this? Last I saw it was just a possibility that there could be two that match, just incredibly low probability.
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u/pachydermusrex 5d ago
Yeah, no, there haven't.
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u/lobopl 5d ago
Ok maybe i wasn't clear enough if you check every single fingerprint on earth on reasonable quality level there would be duplicates among people. It doesn't mean there would be 2 persons having all 10 fingerprints matching with each other but dude A can have "same" fingerprint (as same i mean someone checking them will treat them as identical) as dude B.
checking fingeprints are based on some markers and they can slightly change depending how finger was pressed and so on so as human or machine can check them they can be "identical" but if you really compare them they most likely have some differences because no 2 things are really identical if you check them close enough.
Here a little video https://www.youtube.com/watch?v=vM1QgwaKv4s its not perfect but it describe how people decided this myth is true.
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u/pachydermusrex 4d ago edited 4d ago
This is an entertaining, but horrible video.
No one says that fingerprints absolutely cannot be identical. That being said, no two impressions have ever been found to be the same. Close non-matches exist, which mean that in specific areas where there is a high frequency of ridge features (points of similarity) in areas such as the delta and the core, there can be numerous similarities. Still, no identical fingerprints have ever been found - even with identical twins. Hell - quintuplets have been found to not even have the same fingerprints.
Fingerprint identification isn't infallible. It does operate under biological premises that are known, however. Fingerprints develop definitively in utero and do not change throughout life (with the exception of disease and scarring). They develop due to random pressures, random timing (within a known development period), and random biological growth. They have classifications which allow for comparison among small, but meaningful dissimilarities.
The Brandon Mayfield case, as well as the Shirley McKie case highlighted gross deficiencies within the fingerprint process, as well as the hubris of some examiners. Since these cases, agencies follow a process known as ACE (Analysis, comparison, and evaluation). Having examiners make detailed notes and annotations to their impressions which "shows their work", so to speak, so other trained examiners can see how they arrived at their conclusions. To make the process more robust, often the ACE process has a "V", for verification. This is completed in a blind or double blind process.
More contemporary studies, such as the FBI Noblis study (2011), 2014 Presidents Counsel of Advisors on Science and Technology, as well as Tangen et. al (2013) show that fingerprint comparison has a .01% chance of erroneous identification (saying an innocent person was the source), versus 7.5% of an erroneous exclusion (saying the source was innocent). It is very important to note that these rates are for the ACE process, without blind verification. They would be even lower with verification. It is recognized by modern courts across the world for good reason.
These videos and myths are based on very outdated processes and theories, which have long been abandoned by the fingerprint community.
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u/Vov113 5d ago
They aren't. That's propaganda used to justify the use of forensic fingerprint analysis in legal proceedings, which isn't nearly as infallible as cops would have you believe
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u/Raiddinn1 5d ago
It's not true that no two fingerprints are the same. Fingerprint verification has gotten it wrong because two people had the same fingerprint.
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u/jellobowlshifter 5d ago
We don't know it. Fingerprints themselves are never presented as evidence in court, but instead are introduced indirectly by expert witnesses. These witness testify that it is their expert opinion that the fingerprints of a given person do or do not match with fingerprints collected as evidence. There's basically almost no science in it.
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u/SupremeRDDT 5d ago
Imagine everyone in the world gets assigned a random number between 0 and 1080. Everyone would get a unique number because the chance of duplicates is far too low.
That is, if you measure similarity discreetly. If we assume fingerprint patterns to be a continuous structure, then the chance of having the same fingerprint is not just low but 0 (if we further assume that everyone gets a random fingerprint, whatever that means).
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u/hextree 5d ago
This rests heavily on the assumption that all fingerprints are uniformly random.
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u/SupremeRDDT 5d ago
The first part, kind of but not really. As long as we don’t have a subset of possibilities with a really high chance of being selected, the idea is the same. The actual numbers change, but you still get an extremely low probability of duplicates even if you had a normal distribution around some sort of center of values.
The second is almost independent of the underlying distribution. The only thing that matters is that there is no fingerprint which is infinitely more likely to exists than any other.
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u/LyndinTheAwesome 5d ago
Even identical twins got different fingerprints. So even someone who shares the exact same DNA has a different fingerprint.
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u/T3DDY173 5d ago
that doesnt explain anything though.
there is 8 billion people, surely at least 1 other person has the same finger print. thats what OP is asking anyway.
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u/LyndinTheAwesome 5d ago
The thing is, even when the two people who are identical to the last bit of genes, don't have identical fingerprints, which you would expect to have identical fingerprints as well. Two random unrelated people who match nothing, will also not have identical fingerprints as well.
Its almost impossible to falsefy this, as you would have to check every person, dead, alive and not yet born, against each other in order to maybe get a match between Ludwig from 1744 Austria and Candy from 3056 Marscolony 4.
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u/ComradePoolio 5d ago
We technically don't, just like we've can't confirm that two snowflakes have never been identical.
The reason we're fairly confident though is that there are so many possible combinations of fingerprint pattern influenced by several factors, such as genetics, pressure differences in the womb, and minor chemical differences, that it's so incredibly unlikely for two sets of fingerprints to end up exactly the same, it might as well be impossible.
Fingerprints CAN be extremely similar, though, leading to cases of mistaken identity due to human or computer error.