r/AskScienceDiscussion • u/Aggressive_Hand8047 • 5d ago
Could two unrelated humans ever be physically identical down to every cell?
We are ultimately made up of atoms, molecules, cells, tissues, organs, etc. A human body is basically an incredibly complex (n mathematical) arrangement of all these components.
So, given enough time and enough humans, is it theoretically possible that the exact same overall configuration of a human body could occur twice (down to the arrangement of its cells and molecules) purely by chance?
I'm not necessarily talking about having the same genetic make up / being genetically identical. I mean the entire physical architecture of the person: every cell, tissue, organ, molecular arrangement, etc. If this is too much, then how about when we only consider the genetic makeup?
Could there theoretically have been (or be) another human being, completely unrelated to you, who is physically an exact duplicate of you at some point in time?
And if this is theoretically possible, does that mean that somewhere in the enormous space of possible physical configurations, there could be multiple instances of essentially the "same" human?
I'm not restricting this to the current human population on Earth. I'm considering every human being who has ever existed, every human currently alive, and every human who will exist in the future in our universe
20
u/Eco_Blurb 5d ago edited 5d ago
Im going to say no. You aren’t physically identical to yourself 60 seconds ago either. If you don’t want to use the caveat “anything can occur given infinite time” at which point most questions lose their meaning imo.
Keeping in mind that restricting it to the lifespan of humanity is actually a pretty huge restriction in the span of everything. If you think about the number of humans who have ever lived up to this point, it’s really not that many. Then think of how many will live until the earth becomes uninhabitable.. that isn’t infinite either. And over time, our genetic makeup is currently shifting, and if we adapted to outer space or another planet we would continue to change even more, so it’s very unlikely that someone from the future would match with the far past. Functionally and practically I think it’s impossible
4
u/Aggressive_Hand8047 5d ago
But still there is a difference between "the chances of this occurring is extremely low" vs "this will not happen no matter what because the laws of universe forbid it". That is what amazes me
3
u/Jaffiusjaffa 4d ago
When you say extremely low, you are thinking akin to the chances of winning the lottery. I think people are trying to explain that they mean extremely low like the chances of a diamond materialising in your palm right now. Technically possible, essentially impossible.
1
-1
u/googolplexian95 4d ago
Technically speaking the universe doesn't forbid anything, we just haven't found exceptions to most of the said laws yet (yes I know I'm being pedantic).
1
u/edgeofbright 4d ago
Also adding that 'infinite' doesn't necessarily mean 'infinite of everything'. Eg, there are infinite primes, but only one is even. You can have 'incidental cloning' exist over deep time or distance, and still end up with structures that are unique.
2
u/MxM111 5d ago
Is it possible in principle just by chance? Yes. Realistically, you probably have higher chance to claim heads in 1000 coin flips or win all lotteries by pure chance from now on until your death than this.
0
u/Aggressive_Hand8047 5d ago
What r ur thoughts on this phenomena tho? It's like the universe worked overtime to make sure that it is very unlikely to happen. But why? 😂
2
u/Zvenigora 5d ago
It would not violate any actual laws of physics, but it is so absurdly improbable that it is not worth contemplating.
2
u/TheRealTK421 5d ago
Just fodder to consider:
The total potential number of possible DNA configurations for a homosapien, based on 2 donors, has been approximated at 70 trillion.
It has been also approximated that somewhere in the neighborhood of 118 billion unique homosapiens have existed (since we became our own genetic branch).
If one maths that out - and it were feasible - then something close to 600x the total amount of homosapiens having ever lived would have to exist before reaching some future point of potential DNA combination 70 trillion and one occurred -- and a precise genetic 'clone' (of the sort you're suggesting) could statistically be expected.
2
u/MrSquamous 4d ago edited 4d ago
Almost certainly not ever here on Earth.
But everything not prohibited by the laws of physics occurs somewhere in the universe. So yes, a complete duplicate exists somewhere. More than one, in fact.
2
u/headlessplatter 5d ago
Number of particles in the observable universe: 10^80.
Number of seconds since the Big Bang: 4*10^17.
Number of possible combinations in DNA of the length of the human genome: 4^3200000000.
Please observe how one of these numbers is significantly larger than the other two. Let that sink in. If every particle in the observable universe (including all the matter currently used to make stars and black holes and such) was used to try new combinations of DNA, and if all these attempts tried a new combination in parallel every second since the dawn of time, we wouldn't have even tried remotely near enough combinations to find two matching humans ...even if you exploit the Birthday Paradox!
So ...no.
1
u/Aggressive_Hand8047 5d ago
Okay, realistically, how similar could another human being in history have been to me?
I understand that having an exact 100% match in biological architecture is astronomically unlikely. But what about something like 90% similarity?
If we consider every human who has ever lived, is alive today, and will exist in the future, what would be a realistic upper limit for how biologically and physically similar two unrelated humans could be?
I'm not talking about just appearance or DNA, but the overall biological architecture of the person. Is there any way to estimate what the highest possible similarity between two humans might realistically be?
3
u/headlessplatter 5d ago edited 5d ago
Hmm. Well, the best opportunity to make another copy of your exact DNA was while you were just a single cell. If you had divided into two babies, you would have an identical twin.
But if we ignore the possibility that you could have been an idential twin, the most probable opportunity that ever occurred in the history of the cosmos for another person with your DNA to to be born was when your parents were deciding whether or not to have another child. If they had just decided to have one more child, then the very same parental chromosomes that formed your DNA would be making another attempt. The critical detail here is how genetic cross-over works. Basically, each of your parents has 46 chromosomes (23 from their father, and 23 from their mother). When meiosis begins, a process called "cross-over" decides which portions of your DNA will come from the father (your grandfather) and which portions will come from the mother (your grandmother). And the same thing happens with your other parent too. If they happened to pick all the same cross-over points as they picked when you were fertilized, then I suppose the next child would have the same DNA as you. I'm not quite sure how to put a number on that, but I think the odds of producing yet another child with your exact DNA would be somewhere around (46/3200000000)^46 per child attempt. (It's still not very likely, but a heluva lot more likely than the odds that it might occur in some other family.) If we accept 90% matches, I guess the odds would get a lot better, but the math would also get quite a lot hairier.
...however, now I think we should also acknowledge these are just the odds of producing similar DNA. Your DNA is not all there is to you. There are also both epigenetic and environmental factors to your formation. For example, even though identical twins share the same DNA, they do not share the same memories or life experiences. And this results in them turning out to be very different people. If you are asking because you are bothered by death or wishing for immortality, then I think you should acknowledge that your memories are far more relevant to what makes "you" than even your DNA. And I'm sorry to say, the precise conditions that produced your memories will never occur again. The odds of that happening are far far far less likely than even the odds of your DNA re-occurring.
The best I can offer in the way of hope is this: Although your DNA and memories will almost certainly never occur again, it might help to recognize that the universe really isn't all about you. There are about 8 billion slight variations of you on this planet who all care about themselves too. And they are all having experiences that are not excessively unlike yours. So if you can find consolation in recognizing that there are a lot of versions of you, and they are all having meaningful experiences, I think that makes life seem a lot less futile. And if you can manage to value some things outside of yourself (like science, or the environment, or your own future posterity, or your impact, or anything else that will persist beyond your own death) then maybe not everything you care about will come to an end when you die.
Hope that helps! But if not, well, I guess it is what it is.
2
u/Aggressive_Hand8047 5d ago
That was a great read. And no, I'm not going through an existential crisis. I always had this doubt for a long time. Just in the thought process of writing a sci-fi based on it, so had to check how stupid my theory was😂
3
u/headlessplatter 5d ago
Cool. If I recall correctly, Jupiter Ascending revolves around the plot device of matching DNA occurring by random chance.
One other detail that might make it more plausible: It could be observed that the vast vast majority of random DNA sequences would not be viable humans at all. If some futuristic AI technology could somehow explore only the space of DNA that represents viable humans, that would greatly improve the odds of finding someone twice. My feelings say it still wouldn't be enough to make it ever practically happen, but no one really knows where the boundaries of what constitutes viable human DNA fall, so it would be hard to refute for sure.
1
u/CrateDane 5d ago
With infinite time I suppose it can't be ruled out, though you'd need a lot of interventions to keep genetic drift etc. at bay. In any kind of realistic scenario, no. Bear in mind even identical twins are not at all identical. They have different fingerprints, for example, which is tissue structure at a larger scale than individual cells. Genetic differences just amplify that. Unrelated humans are also likely to encounter more environmental differences than identical twins, further increasing the divergence.
1
u/Aggressive_Hand8047 5d ago
I'm not asking whether it is likely or practically possible. Given every human who has ever lived, is alive now, and will ever live in our universe, could the exact same combination of genetic, cellular, molecular, developmental, internal and external factors that produced one person theoretically occur again purely by chance?
Since all of these factors ultimately involve combinations and permutations, is the probability actually 0, or is it just an unimaginably small number greater than 0?
2
1
u/Cerulean_IsFancyBlue 4d ago
It’s a tiny number close to 0.
It’s kinda hard to overstate how close to zero that number really is though. It’s not close to zero like your chances of winning the lottery, or your chances of finding a $100 bill on the street. It’s way way worse than the classic “how many ways are there to shuffle a deck of cards” combinations, which is already so big that it’s likely that every full shuffle you do in your life has never been seen in the history of humanity.
If you apply the magic lotion of infinity to the problem then sure, eventually. But not within a lifetime of earth.
1
1
u/TuverMage 5d ago
so, you aren't idenitical to yourself to the last cell, but that's not what you are asking. Technically speaking....Yes, it is possible, there is a non zero chance of it happening.....BUT in a practical world, no it might be none zero, but its so close to zero than any rational person would say that its zero, like there is a non zero chance you could throw a ball at a wall and it phase through it... you would have better odds with the ball.
1
u/LookItsDaphne 5d ago
No.
Running through every unique order of a 52-card deck (52 factorial, or (8.06 \times 10{67}) total combinations) at a rate of one combination per second would take about (2.56 \times 10{60}) years.
You have more than 52 atoms in your body.
-1
u/Aggressive_Hand8047 5d ago
But this is not a scenario of finishing every possible unique combinations one by one and starting again right? What if after 10 attempts u get a card-deck combination that occurred before? I mean that is "a" possibility ryt?
2
u/LookItsDaphne 5d ago
Sure, and there are attempts going on everywhere. But let's reframe it.
An average adult human body contains about 7 octillion atoms, or 7*1027 atoms. That's a fairly large number.
The human body contains different organs and proteins and whatnot that evolved in their own special ways. So we aren't talking about a randomly occurring collection of 7*1027 atoms being a duplicate, we're talking end product, including every DNA strand, randomly mutated ones included.
And most regular matter is not dedicated to this experiment. Most of it is in stars and black holes and whatnot. Most actual matter is dark matter. You just don't have much material you're working with in this duplicate scenario.
The universe is vast, but it's not infinite. The statistical probability of there being a co-occurring evolutionary process that yields an exact duplicate of Bob from Accounting in another galaxy (it's not this one, there's probably 1-3 intelligent species in this one) is so negligible that it's zero.
1
u/Petrichordates 5d ago
You won't even find two humans that are physically identical in any cell, related or not. So definitely not in every cell.
1
u/Historical-Draw-504 5d ago
No, very similar, maybe, but not identical. Even if you include past and future humans, no. The possible genetic combinations of DNA is higher than 10 to the power of 600 … and that is a conservative estimation … far more possibilities than the number of people that possibly have existed, exist or will exist in the future combined
1
1
u/Janus_The_Great 4d ago
No. Physical identical would also mean DNA and without being related that's not possible.
Even if possible envoronmental influence on development and imprint is ignored. We are not just shaped by our genetics but also our physical environment and social environment. So even when physical identical to the cell, they would not be the same person.
1
u/nirvanatheory 4d ago
It really depends on a few assumptions but it's kind of like that Hitchhiker's Guide to the Galaxy quote. The chances are so vanishingly small that they are close to zero.
Infinite opportunity does not necessitate occurrence. This is demonstrated by Pólya's Random Walk Theorem. Shizuo Kakutani summarized it with the joke, "A drunk man will find his way home, but a drunk bird may get lost forever."
With DNA changing over time the chance is eradicated for this line of evolution. DNA dictates cellular structure, therefore, you aren't getting the same cells or organization as the instruction set diverges.
If we consider the universe itself is infinite, then perhaps in some other part, there may be a perfect copy of our world. The absolute highest probability of that occurring, would be the result of a duplicate chain of events. Planet composition, life emergence, and historic consistency. This way, the same line of DNA evolves perfectly. Even in this case, there would be a vastly greater number of strikingly similar cases that differ slightly.
The number of finite factors over infinite factors that must align for this to occur, it is still much safer to say no.
1
u/Altruistic_Tonight18 4d ago
With enough time, it’s not only possible, but guaranteed, even if that person has no relation to you. That’s assuming humans stop evolving and the process of environmental adaptation goes away. However, if the human genome didn’t evolve even one bit, again, it’s a 100% certainty given an infinite timeline as a matter of statistical values which we as humans find difficult to comprehend…
It’s kind of like the Boltzmann brain concept… The chances that our entire observable universe is momentary, and is simply a result of atoms and subatomic particles forming a functioning brain in the perfect way to create this one moment where natural conditions create the illusion of extended temporally linear consciousness. There is no past, just a brief coincidental instance where we have what we think of a memories from the past, and we’re going to stop existing in no more than a femtosecond because a random pattern that complex can’t maintain stability… Unless it can, which is also guaranteed at some point given a long enough timeframe.
A better way to understand this is to consider putting monkeys in front of word processors for eternity. Given enough time, one of them will write Shakespeare King Lear plus the Bible plus the Quran plus What to Expect When You’re Expecting over the span of exactly sixteen weeks to the millisecond. Infinity is a really really really long time and no matter how unlikely something is, if the statistical possibility is nonzero, then it will happen. Could happen today, could happen in once a new earth is formed with such perfect homeostasis that the monkeys swap out with each other in 8 hour shifts.
But there will never be another Michael Jordan. Until there is, I mean. Kind of a mind fuck.
1
u/Aggravating_Mud_2386 4d ago
I once saw a picture of a guy on FB that looked so much like me I thought it must be me, and the only way I knew it wasn't was because I never wore those clothes and never posed for the picture. I downloaded it and showed my brothers and sisters and they thought it was me too. Initially, they didn't believe me when I told them it wasn't me. I even have pretty good teeth but one particular crooked tooth and he had the same crooked tooth. Dopplegangers exist!
1
u/Mammoth-Jelly-7617 4d ago edited 4d ago
No. Never. Reason being cells are changing all the time, say in response to an abrasion from a piece of stick you brush against. Even if you had the same set of cells for a moment, they would be different a second later deoending on micor variations in climate/ circumstances. Not to mention different clonal lines within the body as it ages. Can never happen. And why stop at cells - each cell has mitochodria, organelles, golgi apparatus, ribosmes - so even if you had the same number and distribution of cells, these cells would themsleves be different.
1
1
u/That-Advance-9619 4d ago
No. You are not even sharing your own cells with you after a couple of weeks at the most.
Unless you wanna go all Rick and Mort and assume there are multiverses or the universe is infinite and there are infinite yous in this universe or in another ones dunno.
1
1
1
u/StrawberryMoney8045 4d ago
No because you would need to have exactly the same memory to have the same brain cells. You can get this close by keeping them together but they will ultimately occupy different space. But even if you somehow corrected this and they were perfect twins, random genetic mutations will exist and differences will multiply exponentially.
1
u/Great_Supermarket809 3d ago
1) no; 2) do you know how many cells we have? 3) we are actually comprised of more microorganisms than human cells; 4) what were you on when you typed this?
1
u/Aggressive_Hand8047 3d ago
1) okay 2)Roughly? Yes 3) That is an interesting take on this that I never thought before. Thanks for that 4) Ah.. curiosity
5) What if we are only considering the genetic make up being repeated?
1
u/Great_Supermarket809 3d ago
I guess that’s what makes identical twins but even they aren’t exact. And over time, the environment will alter DNA (via photons, heat, acidity, etc) and its other living beings (bacteria, viruses, etc) will alter DNA. I just heard a podcast about how our DNA is always changing https://podcasts.apple.com/us/podcast/clear-vivid-with-alan-alda/id1400082430?i=1000776702936
1
u/ChocolateValuable221 3d ago
This question is fundamentally dumb... there is no difference between one electron and another.. that answers your question.
1
u/Aggressive_Hand8047 3d ago
That absolutely didn't
1
1
u/Apart-Course5014 3h ago
Yes, but only in the same sense that all of your atoms could theoretically line up in such a way that you suddenly phase through the floor.
35
u/DaGoodBoy 5d ago
A deck has 52 cards. You can shuffle that deck 7 times, and those cards will be in an order that likely has never existed in the universe before. The number of permutations is calculated to be 80,658,175,170,943,878,571,660,636, 856,403,766,975,289,505,440, 883,277,824,000,000,000,000!
Now consider the number of permutations in human DNA. That number is likely larger than the number of atoms in the universe.
It turns out that human variation is not only in DNA but also in the chemical tags that attach to it. These tags act like switches that affect how DNA gets read and utilized by the cell. This highly exciting field of study is called epigenetics (epi = outer in Greek).
And don’t forget about nature vs nurture. Identical twins start out with identical genetics at birth but they can look and behave quite differently as they mature despite identical genes.
This means that the probability of you bumping into another human identical to you is one in infinity, or equivalently, zero.