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StoneSoup

Perhaps We're All Related

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Interesting thought experiment. Think of your ancestral "tree". You had two parents, they each two parents, and so on - all the way back.

 

Assume 25 years (on average) between ancestral generations.

 

If the number of ancestors doubles each generation, then basically - to figure out how many ancestors you had at any generational level in the past, you just multiply back by two.

 

Well, if you multiply out 2n where "n" = number of generations, then after 31 generations, each person had 1,073,741,824 ancestors. Multiplying 31 generations x 25 years = 775 years - or the year 1240 A.D., counting back from 2015.

 

According to https://www.census.gov/population/international/data/worldpop/table_history.php , the world population in the year 1250 was unlikely to have exceeded 450,000,000 people - and Earth's population did not hit 1 billion until after 1750.

 

I'm not sure exactly what this means - but it seems very likely that most of us have common ancestors within the past 300 years or so (just 12 generations back).

 

I invite criticism - because this story seems too easy - and also too unlikely.

 

Cheers,

SS

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Well the god-botherers think we have only two ancestors. Caucasian. I can only guess how that makes non Caucasians feel.

 

Science thinks we came out of Africa and from a linear progression genetically.

 

Now we've found Neanderthal DNA in modern man, we can understand that this progression was not purely linear.

 

Currently, the best answer is that hominids (ape like creatures that demonstrate manly ancestor traits, but not actual apes, they're a bit different) were originally from Africa, but were several or many species. Think seagulls, many similar species. Some interbred, some did not, some travelled, some did not, then some interbred again and so on.

 

Regarding racial variation, look at dogs, or cats, from an initial gene pool, many different forms and colours, indeed, temperaments and capabilities can be bred in a small number of generations. Imagine what fun you could have if you wanted to selectively breed humans.....

 

But to the initial question posed: whilst mathematically, you can work out the likely number of ancestors, for a given number of people, and posit that at a certain point the number of ancestors is finite and therefore all the same people, what you have to take into account is that variation results in diversity.

 

Diversity, results in not only different, but unsuccessful and unrecognisable. So if the rate of diversification is greater than the rate of procreation, the likelihood of being able to pin down certain group of ancestors for all of us, is low.

 

Except in isolated instances, (e.g. Pitcairn Islanders, the progeny of the Mutiny on the Bounty survivors) humans tend to breed like rats and select mates on quite un-genetic grounds. This in my view tends to suggest a pool of ancestors that is wide and varied.

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You are assuming each person has different parents. Everyone would have no brothers and/or sisters.

 

No - I'm assuming that at each level of the ancestral record, each ancestor was the result of a mating between a male, and female, roughly 25 years older that the individual. This is pretty much an undeniable truth - and it does not matter if there were siblings to any ancestor, or any "neighbors" who did not generate offspring. Doubling the "mating players" involved at each layer of anyone's ancestral tree gives a minimum population needed to produce each that succeeding generational layer.

 

The only assumptions needed are that:

 

1) Children did not mate with their parents

2) Children did not mate with their siblings

 

There would almost certainly have been some occurrence of those situations -but I am figuring that for at least the past 800 years, the taboo against close incest has predominated.

 

SS

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Stone, if humans had "Access" to all other people, or near access, then I'd agree 12 generations. However many groups are very remote and nointeraction.

 

There was an exhibition a number of years ago "How the rise of the bicycle saw the fall of the village idiot"

 

Interesting show as it showed how the gene pool was very small in many British villages that lived a long walk away - too far to court or arrange marriages so they happened within the village.

 

WIth the invention of bicycles, men could wonder far further and spread the gene pool

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"How the rise of the bicycle saw the fall of the village idiot"

 

​I like that, probably about the same time, fish realised they needed bicycles :)

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No - I'm assuming that at each level of the ancestral record, each ancestor was the result of a mating between a male, and female, roughly 25 years older that the individual. This is pretty much an undeniable truth - and it does not matter if there were siblings to any ancestor, or any "neighbors" who did not generate offspring. Doubling the "mating players" involved at each layer of anyone's ancestral tree gives a minimum population needed to produce each that succeeding generational layer.

 

The only assumptions needed are that:

 

1) Children did not mate with their parents

2) Children did not mate with their siblings

 

There would almost certainly have been some occurrence of those situations -but I am figuring that for at least the past 800 years, the taboo against close incest has predominated.

 

SS

 

But you are forgetting about cousins marrying and it doesn't take 1st cousins to throw off your calculation.

 

For example consider Easter Island. It was 1st settled by Polynesians around 400 AD. It never had a large population that your calculation implies.

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The only assumptions needed are that:

 

1) Children did not mate with their parents

2) Children did not mate with their siblings

 

There would almost certainly have been some occurrence of those situations -but I am figuring that for at least the past 800 years, the taboo against close incest has predominated.

 

SS

 

I guess West Virginia is the exception that proves that rule right, or is it Arkansas?

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Guest

I don't know if this is total nonsence or not, but heard once that everyone shares part traces within their gentic code, traced back to just five or six different individuals at some point. There must have been a point somewhere in human history, where there were hardly any humans around, so technically it could be a lot of peope today must be related, however distant.

 

Interesting topic...

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The US population at the 1790 census (the first) was just 3,929,214. Of that number, 694,280 were slaves and another 59,150 "free persons of color". If you are an America with colonial ancestry (as my father's family is 100% and my mother's about 25%), that means the odds of your being related to the others is very high. Also, if your ancestry is Southern or New England, you are drawing on an even smaller ancestry pool. I have found that I'm a 4th to 6th cousin of several of my friends in the States. And since the importation of slaves was banned by federal law in 1808, the odds of African Americans being related to other is probably very high.

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