
Why don’t identical twins have identical fingerprints? - fgeorgy
http://qi.epfl.ch/en/sondage/show/257/
======
rtl49
The article doesn't answer the question in any satisfying way. A layman would
probably believe that the environment in the uterus is the same for both
twins, too. The "satisfying" answer is still quite boring: as with everything
else, there are stochastic processes in play during embryonic development. For
one, cytoplasm is divided asymmetrically, so the two embryos don't begin their
separate journeys with a perfectly equal share of their progenitor's
resources.

Also, this is a rather silly sentence:

 _Although very similar, the fingerprints of identical twins are nevertheless
unique because they are not completely determined by genetics: they are an
example of phenotype, which refers to the physical characteristics of an
individual that are determined by the interaction of genes and the
environment._

By this reasoning, the only thing _completely_ determined by genetics is
genes, since every manifestation of genotype could be called a phenotype.

~~~
dragonwriter
> By this reasoning, the only thing completely determined by genetics is
> genes, since every manifestation of genotype could be called a phenotype.

But this is absolutely correct, so the fact that the sentence leads to this
correct conclusion doesn't make it silly. Genotype is just genes. The
manifestations are all determined by the interaction of genes with the
environment and the manifestations of observable traits together make up the
phenotype.

Some aspects of this are practically tightly controlled by genes because the
environments which allow an organism to develop at all tend to also be ones in
which the genes involved are expressed in certain ways, and some are less
tightly controlled by genes, because there is more practical variation in
interaction with the environment. But these are differences of degree.

~~~
rtl49
There's no substantive point of difference between my post and yours. I'm
simply suggesting that perhaps the "big reveal" for this question is a bit
trivial, even for the general public. Everyone knows that no matter a boy's
genome, he isn't going to grow as tall as Yao Ming if he only gets 1200
calories per day in his diet.

------
the_ancient
I still love how people simply assume fingerprints are unique even though
there has never actually been any studies with a large enough sample size to
make that determination

Fingerprinting, at least for the purposes of criminal investigations is
pseudo-science at best, akin to the now debunked microscopic hair analysis.

DNA is always given as a probabilistic statement "there is a 1:1,000,000
chance this DNA belongs to someone else"

However with fingerprints, like microscopic hair analysis, it was simply
match/no match... a binary state that is given far far far more weight than it
should. The perceptions of the examiner weigh heavily on the outcome.

Finger print examining is an art form, not a scientific discipline

~~~
fractallyte
How could they be anything other than unique? A fingerprint is a 'function' of
a unique individual. You might as well claim that human faces aren't unique.

Bear in mind, of course: the degree of uniqueness between two samples is
determined by the metrics used to distinguish between them. I don't know the
state-of-the-art with fingerprint analysis, but with a purely physical
measure, how can fingerprints _not_ be unique?

~~~
dalke
Many people have problem telling identical twins apart, so under that metric
it's true that human faces aren't globally unique. There's even a project to
find "twin strangers", which has had some success (see the images at the
bottom of [https://twinstrangers.net/](https://twinstrangers.net/) , though
they also had the same makeup applied, which makes them look even closer).

> how can fingerprints not be unique?

How can the hash of two different strings be the same? It's all part of the
Birthday Paradox, combined with that it means two identify two physical
objects as the same thing.

Now, at some point no two human-scale objects are the same. Even with two
mass-produced objects, there are slight variations in production because of
non-zero tolerances. For example, two sequential $1 bills differ of course by
the serial number, but also contain minute differences in the paper.

So as you say, we need to distinguish between how fingerprint analysis is
done, vs. the most detailed possible analysis. And we know of several cases
where fingerprint identification has been incorrect. One is Brandon Mayfield,
a US attorney who the FBI believe, on the basis of a fingerprint match, to
have been one of the Madrid bombers.

As a result of that case, and similar ones, people have started to ask the
police and others for data which shows that "all fingerprints are unique" is
really true. This myth started over 100 years ago, but was based on a small
sample size. There's never been the analysis needed to figure out the actual
error rate, especially if there are, say, 100 million entries in the system.

See also
[https://en.wikipedia.org/wiki/Fingerprint#Validity](https://en.wikipedia.org/wiki/Fingerprint#Validity)
. And notice how that Wikipedia page also includes "No two fingerprints have
ever been found identical in many billions of human and automated computer
comparisons. _[citation needed]_ ". Where is that citation?

------
fitzwatermellow
It's not just the fingerprints. Entire organs may grow according to the
elegant mathematics of reaction diffusion systems. Not to mention metal
alloys, igneous rocks, suns, galaxies, and so on...

A mathematical theory proposed by Alan Turing in 1952 can explain the
formation of fingers

[http://phys.org/news/2014-07-mathematical-theory-alan-
turing...](http://phys.org/news/2014-07-mathematical-theory-alan-turing-
formation.html)

------
Animats
Plants can be cloned easily, but the leaf and stem patterns don't match
exactly. Those are generated by a statistical process and can be simulated
with an L-system.

The human genome is only about 3.2GB. All the fine detail can't be in there.

[1]
[https://en.wikipedia.org/wiki/L-system](https://en.wikipedia.org/wiki/L-system)

------
alister
> What purpose do fingerprints serve? Apart from improving our grip on
> objects...

This has been partially debunked[1][2]: _The area of skin in contact...was
always 33% less than if the fingerpads were completely smooth. This confirmed
that fingerprints do not improve our grip, because they actually reduce our
skin 's contact with the objects that we hold._

I say "partially debunked" because it might improve grip on wet surfaces:
_They may allow water trapped between our finger pads and the surface to drain
away and improve surface contact in wet conditions._

It seems similar to the situation with tire treads. If you ask most people why
tires have ridges and valleys, they'll say that it improves grip on the road.
But if the road is dry, you'll get bigger contact area and therefore better
grip with completely smooth tires. In fact race cars use completely smooth
tires for better grip (when the racetrack is dry). Tire treads exist to
conduct away water when the road is wet, and they improve grip only in that
situation.

In an interview with the co-author of the friction study, he made some
interesting speculation about the purpose of fingerprints: _My preferred
theory is that they allow the skin to deform and thus stop blistering. That is
why we get blisters on the smooth parts of our hands and feet and not the
ridged areas: our fingerpads, palms and soles._ [3]

[1]
[http://newsvote.bbc.co.uk/mpapps/pagetools/print/news.bbc.co...](http://newsvote.bbc.co.uk/mpapps/pagetools/print/news.bbc.co.uk/2/hi/health/8093134.stm?ad=1)

[2]
[http://jeb.biologists.org/content/212/13/2016](http://jeb.biologists.org/content/212/13/2016)
(actual paper)

[3]
[http://www.manchester.ac.uk/discover/news/article/?id=4715](http://www.manchester.ac.uk/discover/news/article/?id=4715)

~~~
sanoli
Well, they should test _actual_ grip, instead of percentage of skin contact.
So what if it is 33% less? What if it somehow grips better having the prints
(as might be the case on wet surfaces)? Also, don't go testing in some
material that was never touched upon by early humans.

~~~
alister
> they should test actual grip

Well, the referenced article says that that's what they did (in addition to
further measurements to determine area of contact).

------
raldi
Upvoted for asking a question in the headline and then immediately answering
it in the first sentence of the article.

~~~
iheartmemcache
EPFL in the top 15 unis in the world almost consistently in any of the
sciences. For CS and mathematics, they'll usually rank top 5 with INRIA and
Cambridge, perhaps higher at the graduate level. (I was going to go to attend
for a graduate degree in Algebraic Topology there or but the opportunity cost
and, well, I suppose primarily coming to terms with my own mediocrity made me
decide against.) But yeah, they're not really trolling for hits to generate ad
revenue ;).

Re: one sentence answers - I'm with you. I took this lovely Python module and
pipe most everything that I know [1]will be filler to this
[https://github.com/miso-belica/sumy](https://github.com/miso-belica/sumy).
I've been doing it for a while now and I don't feel as though I am missing out
on anything.

------
epimetheus
I don't know if this is as significant as fingerprints or not, but I have a
coworker with an identical twin, and her sister has Crohn's disease, and my
coworker does not. Chron's is apparently genetic, but there must be some
environmental factors as well.

~~~
DrScump
or it could reflect a damaged microbiome.

------
kelvin0
According the Wikipedia: '...dynamical systems that are highly sensitive to
initial conditions...'

[https://en.wikipedia.org/wiki/Chaos_theory](https://en.wikipedia.org/wiki/Chaos_theory)

------
xg15
You might as well ask why two cloned trees don't have the branches and leaves
at the exact same positions...

~~~
herbig
Except that in your example, the trees are influencing by environmental
factors throughout their life, whereas the first sentence of this article says
it's environmental factors in utero that influences fingerprints.

~~~
rtl49
It isn't a perfect analogy, but it still works. The only reason the other
option, "development is completely random" isn't the right answer is because
of the word "completely."

Honestly, the survey question is poorly asked, and doesn't produce a
particularly interesting discussion. Maybe something was lost in translation.

------
dschiptsov
Because not every factor is genetic. Most of them are environmental and
random.

The best example is with trees. No two trees have the same structure of
branches given that they have the same DNA.

The world is mostly stochastic.)

------
aswanson
Why don't laplacian systems with slightly different initial conditions evolve
in the exact same manner?

~~~
rdlecler1
Robustness is drive by homeostatic feedback loops and/or equilibrium states.
Some systems will act chaotically and will be more sensitive and unpredictable
to changes in initial conditions.

~~~
aswanson
Which gives an answer to the question posed by the post.

------
rdlecler1
I'd like to see how much bilateral variation there is compared to phenotypic
variation between twins.

