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[This video of Numberphile](https://www.youtube.com/watch?v=Fm0hOex4psA) explains it, starting with a simulation using dice to establish some concepts, and commenting papers about the problem (linked in the description). The math involved is a bit complicated, but in one of those papers they calculated that it was some time between 4,000 and 7,000 years ago.




Doesn't migration pretty much guarantee that your hypothetical people don't exist? It would require one group to have been isolated the entire time from when they first branched off to now, with no outside contact whatsoever. The closest I know of is the sentinelese, but how do you know they didn't experience migration before the modern day?




Yeet thanks for the info! Do you have any resources I can look into to learn more about this kind of stuff?


GP misunderstood the original paper. It was about when the last individual who all of living humans are descended from lived. And since it only takes a single event to link even very distant lineages, even with unrealistically low levels of migration, that person lived less than 7000 years ago. It's a basically an interesting but wrong answer to OPs question.


So, 6000 years ago when God created the earth?


No, we're only going back to Noah here, not Adam & Eve.


That arc was my favourite.


As opposed to the one in raiders of the lost ark?


Bask in the glory of the new emperor of the holy redditian empire


It really tied the room together.




oh but how it stank


Nah the earth was created last Thursday. Everyone knows that


So how's your week been so far?


So we are all inbred. Makes a lot of sense now.


Math has already been done. Remember that population growth is not exponential and that this assumes none of you’re ancestors have common ancestors. Ie, if my grandparents were cousins or something, I would have less than 16 second great-grandparents. [Here is the first google result that covers it.](https://www.google.com/amp/s/www.bbc.com/news/magazine-19331938.amp). No math needs to be done as the math has been done many times.


Yeah - it feels very likely that we all have fewer than 4094 ancestors going back 9 generations. I don’t know the probability, but I suspect it’s like the whole “what’s the probability that 2 people in the room have the same birthday?” question.


Also, population was much less mobile even 100 years ago.


The birthday paradox is so crazy.


Sad Alabama noises


Thank God for Mississippi.


Where do you think Mississippi came from? (It wasn't Louisiana.)


*Sad Florida and bud light can opening noises as the humidity rises


>IF my grandparents were cousins or something Totally hypothetical, obviously.


I have seen my family tree going back many generations. At one point a brother and a sister had kids. There were so many cousins too.


Yeah. It’s so common that they calculated the minimum population size requirement in order to have a 95% chance of no genetic defects happening. I think it’s around like 165 is the requirement.


I’m not an expert on this, but it doesn’t grow exponentially like that going backward through genealogy. Otherwise you reach a point the number of ancestors exceeds the population that existed. For example, two first cousins has at most only six great-grandparents instead of the usual eight. This idea is called, “Pedigree Collapse” or “The Diamond Theory”. http://www.olivetreegenealogy.com/misc/ancestors.shtml https://en.m.wikipedia.org/wiki/Pedigree_collapse


it does grow as they are saying but in reality it ends up with less


It grows to a point then it starts to shrink, if you were to write it would it would look like a diamond and not a pyramid


Are you sure it's "at most"? Do you mean "on average" instead? Because I'm sure there is at least one set of first cousins with 8 grandparents instead of 6


Your first cousin is the child of your parent's sibling. That means that two of the grandparents are the same. Each cousin has 4 grandparents, but two pairs are the same people, so there are only 6 unique individuals involved. If you find two people who have 8 unique grandparents, they are not first cousins.


okay but what about when your cousin is also your sibling


This guy incests


You're right, I had it totally wrong, thank you.


What this seem to not ask is how many incest... The population is the largest it have ever being, so this make even less sense... There was a lot of incest in the past.


Incest is not needed. If you marry your fourth cousin your children will have 62 great-great-great grandparents instead of 64. I think that most people who marry their fourth cousins never find out.


What's the average age difference on that?


To cover the "population is the largest it have ever being, so this make even less sense... ," remember that siblings exist and if there are more than 2 siblings to 2 parents **on the global average** then there is population growth. Also, siblings will have the same parents so all the same possible 2048 ninth great-grandparents would be the exact same people and first cousins will have the same grand parents so at least 512 of the possible ninth great-grandparents would be the same as yours as well. Do that with all of your relatives all the way up to descendants of your ninth great-grandparents and you will see it's not that impossible to still have population growth


When learning about coefficient of relationship when doing Punnet squares in a high school biology class, how bad would it be to give an exercise asking them to calculate for the Hapsburg or Ptolemy family tree. That seems like a fun exercise to give that will get the teacher fired.


It's history, it happened, we know it should never happen again, so what's the harm?


Alabama enters the chat… “What ya mean, ‘In the past?” (Unzips pants)


Alabama doesn't actually do that very much. Hell, it's illegal. Pakistan, however... oof. >80%.


\>80% of what?


“>” means greater than. So “>80%” means greater than 80%.


Of what?


Frostadept was being facetious, but in this context it’s >80% of Pakistan.


You're saying that >80% of Pakistani people are inbred?


Someone else is saying that, yes.


Specifically >80% of Pakistan marries their 1st cousin.


But how far do relatives need to be related for being to no longer be an issue?


They made the math wrong. 2^n is the maximal number of ancestors in the nth generation, not the needed number. One may have only 3 grandparents if one's parents are half-siblings, and only 2 grandparents if one's parents are siblings. Now, you don't need to be Sweet Home Alabama to have your number ancestors bellow the maximum. All humans have common ancestors. Few people know their family tree before 4 generations and nobody cares if the person they are fucking is their 10th degree cousin.


This showed up in /r/MadeMeSmile six-ish months ago. [Here](https://www.reddit.com/r/MadeMeSmile/comments/mmsq2y/you_matter_a_lot/gtv8foj/?context=10000) and copied below is my response from then to an "Except in Alabama" joke. ----- It's not even just an Alamaba joke! Exponential growth is untenable. Here's some _very_ back-of-the-envelope examination of just how bad it is! A rough estimate of the number of people that have ever lived is 100 billion people. In a spirit of generosity, let's say that's how many people there were at the start of the common era -- not _since_ the common era, but alive at 1 A.D. For scientific notation, 100 billion is 1e11, or as the relevant exponent, roughly 2^36. If we ballpark a generation at every 25 years, that puts about 80 generations since the start of the common era. This simple model would extrapolate to you having 2^80 ≈ 1.2e24 (a bit over a septillion) ancestors around the start of the common era. If you put a generation around 40 years, you'd have around 50 generations, or 1e15 (one quadrillion) ancestors at the start of the common era. So, in order to reduce that graph from somewhere in 2^50 - 2^80 distinct ancestors to a much more "reasonable" 2^36, you need to fold your ancestry graph on it self somewhere between 14 to 44 times. (But actually more, because there weren't nearly that many people at 1 A.D.) Which means every couple generations, you need some hopefully-distance cousins to be coupling up. All this to say: on a long enough timescale, we're all Alabama.


Which is also why it's meaningless when people talk about how they're "related to Charlemagne" or the like--literally everyone with any European descent whatsoever is, several times over.


Dawkins' example comes to mind (not very accurately though) that an immigrant to an isolated island, given the chance to procreate with the inhabitants, will have something like 80% chance of being the ancestor to every human on the island after 100 generations. Again, numbers are arbitrary. The book's just out of reach right now :P


Still cool, however. I'm generation 40 from Charlie. And don't you forget it! (grabs Spear of Destiny, jumps off horse)


I think about this all the time. I used to think about it when I was in highschool and it gave me major anxiety, self doubt and depression because havving the knowledge that 4000 people of your blood done well for centuries and your failing is hard.


Just the fact that someone is/was able to create offspring, doesn't make them better than anyone else. Think of it this way: out of all the +4000 before you, you're probably the one with the best food, shelter, education and endless possibilities to make your own way and decisions. You're not a failure :)


> Think of it this way: out of all the +4000 before you, you're probably the one with the best food, shelter, education and endless possibilities to make your own way and decisions. Gonna be honest, I think that actually only serves to make depressed people feel worse about themselves.


On the order of a few hundred thousand years for both the male and female oldest common ancestor. https://en.wikipedia.org/wiki/Mitochondrial_Eve


And look what all those 4096 people accomplished in 400 years. A depressed piece of shit who will definitely die before continuing the bloodline.


honey - you're not *THAT* bad - just donate some in a jar & that bloodline lives on!!!


All this work for existence I didn't even want, like knitting a shit sweater to gift someone for Christmas.


i don’t think I was born to be the hope of the future. they weren’t even that smart to overthink like that. My ancestors are some people that didn’t use protection while having sex.


So, this question is difficult because of migration issues, and the nigh impossibility of traveling across the world a thousand years ago. The math seems to work out that every native European is a great(greatgreat...)grandchild to Charlemagne, less than 200 generations ago. The kicker is that we are the grandchildren of every European from then that has any surviving ancestors.* Now, we were completely separated from many other communities. Interbreeding with the Americas was impossible. China very unlikely, etc. Even now there are groups of humans So to get to a common ancestor you will probably have to go back to the very roots of humanity. We simply haven't had intermingled communities for long enough for our DNAs to properly mix. *The math is based on chance. It is possible, but highly unlikely that someone from that time has a single surviving descendant.


Its all simplified here as numbers, but I was wondering if there is any research on how big/small the entire human population for example in europe has been across history?


to the answers below, None of my ancestors until my mother and father thought about "me" as a human, I do not care and I do not have to care about the difficulties of my ancestors just to justify my existance now. That's just like going through hell just to justify being with a megalomaniac, possesive girlfriend, it has absolutely no sense to do that. I say this because I recognise that I'm in a really bad moment of my life, with depression, anxiety and stuff like that and everyone has already told me that I should be "*thankful*" for being alive because of everything that has happened before me, which i do not agree (duh) and it actively makes me feel like I don't "*Deserve*" to even be depressed in the first place. It's not the best way to lighten up a depressed pal, instead i suggest giving the space to the other to vent for a while, really **listen** to what they say and don't try to repair their whole life until they tell you otherwise.




IIRC almost everyone of European ancestry in America is 10th cousin of each other or closer


I would call this wrong in that it seems to say you would have 2,048 different individuals as ninth great-grandparents and that's not how it works. Many of those people would be the same.


I believe you're missing the : suppose none of your ancestors mated with more than one person of the category. Everything else seems legit, i think


How many struggles, battles, difficulties, sadness and all such shit. And it all ended in making... what, me? How disappointing. This is proof right here that all those struggles and shit mean zilch in real world terms to the real world.


Without taking intersecting generations into consideration..... theoretically we live in a world where infinite people have existed. Ultimately this chart is an exercise in how NOT to look at genealogy.


If we go crazy back in time, and following the diamond shape, we don't go back to Adam and Eve right? So this actually means that at some point, one same organism created a second cell or a second organism that merged with each other to create a third one who subsequently merged with one of the previous two or a fourth one, so on and so forth? Or... one organism from a totally different environment was brought to the one living organismo here in Earth and merged with it?


So here's something that throws a wrench in to the works. In some Islamic communities they practice habitual first cousin marriage in the paternal bloodline. Now I only got a C in my GCSEs, so excuse my poor mathematics. But does that change the exponential factor from 2 to 1.5? or would it be 1.75?