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This is about the genealogy of humans.
Mathematical models and computer simulations places the most recent common ancestors (MRCA) of humans alive today to be around 1000 to 5000 years ago. This means that everyone alive today could trace an unbroken lineage back to this individual.
As far as i know the mathematical model used constant population size of 500 million and random mating which is an extremely simplified model. I'm sure the equation would come out pretty simple under these parameters but i suck ass at statistics so i cant think of it. Interestingly, another guy did a complex computer simulation taking into account local mating choices and migration rates between countries and continents as well as population rates according to historical values and came up to a very similar estimate for the MRCA.
Now the Identical Ancestors Point is the time in the past in which (1) everyone is either an ancestor of all living humans at present or (2) has no living descendents at all.
I am a bit confused on how we can come to the Identical Ancestors Point (IAP).
Here is one thing that I found:
http://humphrysfamilytree.com/ca.math.html
**this is using a simplified mathematical model so its alot earlier than realistic models**
"Before 700 AD, every single human is either ancestor of no one alive today, or ancestor of everyone alive today. [Rohde, 2002] refers to this as the "All Common Ancestors", or ACA, point. Obviously if someone in this period is a proven ancestor of someone alive today then they must be ancestor of everyone alive today. So, for example, Charlemagne, because he is a proven ancestor of some people alive today, is probably the ancestor of everyone alive today in the West.
Between 700 AD and 1200 AD, every single human is either ancestor of no one alive today, ancestor of everyone alive today, or ancestor of some people alive today.
After 1200 AD, every single human is either ancestor of no one alive today, or ancestor of some people alive today."
Basically in the simplified mathematical model 1200AD is the MRCA and 700AD is the IAP. I understand that at the time point of MRCA, there will be people who EVERYONE is a descendent of (MRCA himself), people whose ancestors to a subset of today's population, and people who have no living descendents.
Wikipedia gives this:
"Because ancestors of the MRCA are by definition also common ancestors, we can continue to find (less recent) common ancestors by pushing further back in time to more and more ancient common ancestors of all people alive today. Eventually we will reach a point in the past where all humans can be divided into two groups: those who left no descendants today and those who are common ancestors of all living humans today. This point in time is termed the identical ancestors point. Even though each living person receives genes in dramatically different proportions from these ancestors from the identical ancestors point, all living people share exactly the same set of ancestors from this point back, all the way to the very first single-celled organism."
I cant figure out how these people who are ancestors to SOME of today's population disappears when we go back more generations. Surely, there would always be some people who will always fall in that category?
I can see that when we go back in generations from the MRCA's period most of the ancestors will merge, but wouldnt there still be some left who didnt merge with MRCA's ancestors but are still ancestors of the other guy who has some descendents? Damn this is convoluted I cant explain myself. I know im just looking at this the wrong way and its really quite simple, but I just cant quite grasp it. Its at my fingertips but not quite there yet 
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One of my majors is anthropology so I should know about this sort of thing. I don't, so I'll ask one of the biological anth. professors and get back to you if it hasn't been answered. Because this really interests me too.
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On October 23 2011 03:07 Ancestral wrote:
One of my majors is anthropology so I should know about this sort of thing. I don't, so I'll ask one of the biological anth. professors and get back to you if it hasn't been answered. Because this really interests me too.
Especially since your name is Ancestral... hehe.
I'll keep an eye on the discussion but it sounds really doubtful that the IAP is less than 5000 years ago. The Chinese civilization can be traced back 4000 years as well as the Babylonian civilization.
It seems too short of a time period for the ACA to be alive only 1000 years before that point. That person would have to have a lot of progeny who moved very far distances overcoming a lot of severe challenges very quickly.
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uh don't you know what a tree structure looks like? the further back you go, ofc some becomes all as evidenced by the fact that if you were able to go back far enough all lineage could be traced to a single human.
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On October 23 2011 03:42 kingjames01 wrote:Show nested quote +On October 23 2011 03:07 Ancestral wrote:
One of my majors is anthropology so I should know about this sort of thing. I don't, so I'll ask one of the biological anth. professors and get back to you if it hasn't been answered. Because this really interests me too. Especially since your name is Ancestral... hehe. I'll keep an eye on the discussion but it sounds really doubtful that the IAP is less than 5000 years ago. The Chinese civilization can be traced back 4000 years as well as the Babylonian civilization. It seems too short of a time period for the ACA to be alive only 1000 years before that point. That person would have to have a lot of progeny who moved very far distances overcoming a lot of severe challenges very quickly.
Yea, I think a more reasonable estimate today is something like 5000-15000 years. The 700 AD and 1200 AD dates are from the majorly simplified statistical model that doesnt account for normal human behavior and population fluctuations.
Also, seeing as these are statistical projections (retrojections??), so it might not correlate to DNA or anthropological estimates we have. The problem with DNA is that it cannot reliably give you the MRCA in the literal sense. You can track down individual genes or chromosomes, but thats following the lineage through one SINGLE factor. Autosomal genes wouldnt reveal much on their own since they recombine and change so much. Maybe if you look at the whole genome at once, it could produce something meaningful.
Well, there is the so called mitochondrial eve and y-chromosomal adam which we get from following the mitochondrial dna and Y chromosome, respectively. These genes do not undergo genetic recombination so any changes to them can be attributed to mutations. Since we know the relatively constant rate of mutation, we can extrapolate back. Eve dates back to something like 150,000 years ago and adam 60,000 years.
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"Before 700 AD, every single human is either ancestor of no one alive today, or ancestor of everyone alive today"
This honestly can't be true, I highly doubt every single person in Australia or pure Africans are somehow descendants of the same people as pure blooded native Americans as they didn't come into contact for another 700 years.
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On October 23 2011 05:05 repsac wrote:
uh don't you know what a tree structure looks like? the further back you go, ofc some becomes all as evidenced by the fact that if you were able to go back far enough all lineage could be traced to a single human.
Well yea, that would be the most recent common ancestor. Now this guy wasnt some lone human from outer space, all it means is that he is the person that everyone alive today originated from. He lived in a society with many other humans of his time. Its just that everyone else's offspring eventually died off. If we go back 100 years from today, the MRCA would be someone way before the one we have today. If we go back to something like 1400's, before migration became more common, the MCRA would have to be ALOT older since there was not as much intermixing of cultures.
If your talking about the lowest common ancestor, then umm yea, that would be the point at which speciation happened. And even that is looking at it too simply. A Speciation event can arise from a single organism. Its something that happens to a population in isolation over many generations. So there is no first human in the literal sense.
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I'm sorta confused what the OP is asking....but all of those numbers look far far far too recent to me. I mean, think of all the various tribes around the world that have had almost no contact with the world at large for centuries if not millenia. I would honestly not be surprised if the MRCA was significantly above 10000 years.
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Like i said, its just statistical model using random mating, obviously it would be more recent than anticipated. Be that as it may, the concept of MRCA and IAP exists. Regardless of the timeline what im wondering is how one goes from MRCA to IAP, i cant quite grasp that concept.
But then again, it might not be all that difficult to perceive that at one point some random dudes sailed across to some remote tribe and assimilated. All it takes is one individual to mix the gene pools.
If you consider only the western world, where you pretty much had random mating, you could probably say that every single person alive today is a descendent of Charlemange, who actually did live in 800AD which coincides with the estimates of that model.
Similarly almost everyone in asia is descended from Genghis kahn or related to his line in some way.
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so that MRCA dude from 5000 years ago didn't mate with other humans in the 5000 years leading to this point? it is almost statistically impossible for the MRCA HUMANS to only mate with other MRCA HUMANS for 5000 years.
rule #1 about statistics: if some complicated analysis comes to a decision that contradicts common sense, it's probably wrong.
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Sweden5554 Posts
The statistical models must not be very good yet then. Taking into account the Y-chromosomal Adam estimate and you have a MRCA with range between 142 and 60 thousand years ago. so the 5 to 2 thousand years ago statistical estimate is off by roughly 3000%....
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On October 23 2011 08:09 salle wrote:The statistical models must not be very good yet then. Taking into account the Y-chromosomal Adam estimate and you have a MRCA with range between 142 and 60 thousand years ago. so the 5 to 2 thousand years ago statistical estimate is off by roughly 3000%....
the Y-chromosome and mitochondrial eve MRCA is misleading. Its not the MRCA in the literal sense of progeny. Eve is basically the "MRCA" for only the matrilineal line. This means that all the women alive today can be traced back to her through their mother's mother's mother's X 1000. This is alot more restricting than the regular MRCA so naturally its way higher.
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Sweden5554 Posts
Ahh, right.
But I can't forego my common sense in that there's some very secluded populations scattered across the globe, especially Polynesia and South America, we haven't had global travel for more than 500 years, only 20 odd generations, doesn't feel enough to reach everyone everywhere. There's still some stone age tribes around the globe who has yet to meet "civilization" that doesn't mean that the genes couldn't have reached them, I just feel that it's not that likely.
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EPT
