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Author Topic:   Hello, cousin! (re: Recent common ancestors to all living humans)
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 6 of 76 (328645)
07-03-2006 6:20 PM
Reply to: Message 1 by subbie
07-03-2006 1:11 PM


comparison to primary article
I tracked down the original Nature article, unfortunately it requires a subscription:
Modeling the recent common ancestry of all living humans.
One thing I'm a bit confused about - the paper is almost two years old, yet the Yahoo news article seems to treat it a recent discovery...
I have a problem with the Yahoo news version of the research - the typical translation-to-laymenspeak problems seem to exist:
Yahoo News version: Furthermore, Olson and his colleagues have found that if you go back a little farther ” about 5,000 to 7,000 years ago ” everybody living today has exactly the same set of ancestors.
Original report version: That is, each individual living at least U-subN generations ago was either a common ancestor of all of today's humans or an ancestor of no human alive today.
"U-subN" generations is an abstract theoretical variable in a simplified model. It does not equal ~6000 years in any real way.
Much of the paper is description of assumptions and simplifications of the model. From the conclusion:
Given the remaining uncertainties about migration rates and real-world mating patterns, the date of the MRCA for everyone living today cannot be identified with great precision.
It would be interesting to see how the mathematical model compares to genetic data regarding the MRCA (most recent common ancestor).

This message is a reply to:
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pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 10 of 76 (329002)
07-05-2006 3:04 PM
Reply to: Message 9 by RAZD
07-05-2006 7:40 AM


Re: mathematic models again?
The mathematics obviously did NOT account for any differences in ability to migrate to different places,
Wrong. The majority of the report focuses on approximating regional differences in migration through history. They also incorporate colonization-related bursts of migration; in other words, they don't entirely assume a constant rate of migration over time.
As an example, the model assumes one-hundred individuals per generation migrate between northern Africa and Italy, while only one individual per generation migrates between New Zealand and Polynesia.
The model is still mathematical, still rest on assumptions, and is thus not an accurate depiction of reality. However, to simply dismiss it as a simple exponential model without, apparently, even examining the model (or even reading the abstract of the paper) is extremely problematic.

This message is a reply to:
 Message 9 by RAZD, posted 07-05-2006 7:40 AM RAZD has replied

Replies to this message:
 Message 11 by RAZD, posted 07-05-2006 9:23 PM pink sasquatch has replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 12 of 76 (329311)
07-06-2006 11:00 AM
Reply to: Message 11 by RAZD
07-05-2006 9:23 PM


wrong again...
That still does not get you over the physical barriers between europe and the americas before columbus,
The model takes this into account - no migration until it starts at a very low rate from Europe to North America via Iceland/Greenland in 1000 AD.
Migration across the Bering Strait region begins at 12000 BC in the model.
North America is not a single unit - migration dynamics within North America are also modeled.
which is then lumped in with the migration rate from New Zealand and Polynesia
Huh? Where the hell did you come up with that one?
I look at the process as described in both the "sensational press" article and what is available in the abstract, and what I see is a model that essentially draws concentric circles around an idealized homogeneous population, and assigns different migration rates to the different radii of the circles in an inverse relationship.
Then "what you see" is wrong, because it does not accurately describe the model, which takes into account historical differences in migration rates within a nodal model. You might realize this if you read more than the abstract and the lay press version of the research.
It is rather ignorant and rude to severely criticize research and researchers without ever examining the actual research in question.
I don't see any correction for geography, and find that rather significant.
You would see that correction if you read the paper.
Read the paper before you criticize.
I'm not going to bother responding to the rest of your post for what should be an obvious reason.

This message is a reply to:
 Message 11 by RAZD, posted 07-05-2006 9:23 PM RAZD has replied

Replies to this message:
 Message 13 by Jazzns, posted 07-06-2006 11:12 AM pink sasquatch has replied
 Message 21 by RAZD, posted 07-08-2006 12:16 AM pink sasquatch has not replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 14 of 76 (329333)
07-06-2006 11:47 AM
Reply to: Message 13 by Jazzns
07-06-2006 11:12 AM


Re: wrong again...
do you think the "made for TV" version of the study does it justice or uses the findings from the study accuratly?
See my message #6 above.
Even though that is not what RAZD is saying, I think that is what he means.
I think RAZD is a smart enough guy to say what he means. I still think it is inexcusable to so severly criticize a model that you haven't examined in any way. The bulk of his criticisms, (which are extensive and detailed), rest on assumptions about the model that are not true.

This message is a reply to:
 Message 13 by Jazzns, posted 07-06-2006 11:12 AM Jazzns has replied

Replies to this message:
 Message 15 by Jazzns, posted 07-06-2006 1:19 PM pink sasquatch has replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 16 of 76 (329391)
07-06-2006 1:44 PM
Reply to: Message 15 by Jazzns
07-06-2006 1:19 PM


Re: wrong again...
Are we all just agreeing differently that the Yahoo article is a misrepresentation if not wrong all together?
Not quite - RAZD is criticizing the model itself, on multiple points claiming that it "obviously" neglects parameters that it actually includes. He does so without having examined the model.
He wrote two fairly lengthy posts, neither of which mention misrepresentation in the lay news article. (I'm not sure why you seem to be defending him; in any case, this is all getting rather off-topic).

This message is a reply to:
 Message 15 by Jazzns, posted 07-06-2006 1:19 PM Jazzns has replied

Replies to this message:
 Message 17 by Jazzns, posted 07-06-2006 1:48 PM pink sasquatch has replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 18 of 76 (329425)
07-06-2006 3:00 PM
Reply to: Message 17 by Jazzns
07-06-2006 1:48 PM


incredulity is not a criticism
I am no expert but it seems very unlikely that the MRCA between myself and a native Australian lived anywhere within a few tens of thousands of years let alone 2-5 thousand years.
It is a result that seems to clash with intuition, as does the conclusion that I'm a distant cousin to sea urchins.
One thing to think about - using a simple exponential model produces the result that the MRCA lived only 800 years ago. Their model pushes this date considerably farther back by adding many more variables.
A second thing to think about when bringing up criticisms - the authors admit that truly isolated populations are a caveat that their model doesn't include. From the News & Views piece on the report:
Jotun Hein writes:
The main weakness in the models comes from migration.As the authors point out,if one region is totally isolated (something that they do not simulate),with no migrants connecting it to other subpopulations,then the universal ancestor must logically have lived before the period of isolation began. Only after that period ends would the dates for the universal ancestor become less distant.
Another interesting point from the primary paper:
These estimates would suggest, with the exchange of just one pair of migrants per generation between large panmictic populations of realistic size, that the MRCA appears in about the year 300 bc, and all modern individuals have identical ancestors by about 3,000 bc. Such estimates are extremely tentative, and the model contains several obvious sources of error, as it was motivated more by considerations of theoretical insight and tractability than by realism. Its main message is that substantial forms of population subdivision can still be compatible with very recent common ancestors.
Even when the authors restrain their migration rates down to 0.1 individuals per generation between continents, (and only during periods when migration was approximated to have occurred historically), it only pushes back the MRCA date a couple of hundred years. In other words, drastically reducing migration rates actually doesn't change the MRCA date all that much - that could be a lacking in the model (I'm no mathematician), or it could be that any migration is sufficient to allow the sort of interrelatedness the model suggests.
Maybe the model is essentially correct, or perhaps it is only correct for 99% of the population today due to pockets of isolated populations. It is important to consider the model and its implications, rather than just disregard it based on little more than incredulity.

This message is a reply to:
 Message 17 by Jazzns, posted 07-06-2006 1:48 PM Jazzns has replied

Replies to this message:
 Message 19 by Jazzns, posted 07-06-2006 4:14 PM pink sasquatch has replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 20 of 76 (329446)
07-06-2006 5:10 PM
Reply to: Message 19 by Jazzns
07-06-2006 4:14 PM


some model details
When using the measure of migration (.1 individuals per generation) is that applied to every possible combination of groups or just the ones that are geographically adjacent?
First, to clarify, the 0.1 value was not some sort of uniform value applied to all groups, it was a specific value applied to a specific transcontinental port during a specific historical period (again, the model is attempting to take quite a bit of complex movement into account).
The model itself isn't uniform - they've run the model many times, changing many of the variables. Running the model repetitively with the same variables does not always give the same result. Assuming that 5% of people migrate from their town gives a result of MRCA at ~1400 BC. They call the 5% rate conservative, but I have no clue how accurate that statement is.
The authors try to model population structure in a simple way by designating towns, countries, and continents as geographical units. It does not appear that they make these units entirely uniform (in other words, different continents have a different town number/distribution). Some intercontinental and intercountry travel requires the use of specific "ports".
They don't use a simple distance radius model, but rather consider each town a node connected in a network to (all?) other nodes by a travel path. They do assume that migration is more likely to take place across short distances than long, so someone who migrates is more likely to do so to an adjacent town then one a few countries (or continent) away.
Possible migrations (especially intercontinental ones) are historically limited by time. Rare migration is permitted across the Bering Strait starting at 12,000 BC, but rare migration across the Atlantic to North America is not permitted until 1,000 AD, as an example.
Populations fluctuate in a historical context as well (as an example, they take into account drastic decreases in Native American populations as European populations increased there).
The model also takes into account lifespan, as well as the number of offspring per individual (there is even a compensatory value for multiple parental partners).
Hopefully that helps a bit in clearing up the level of the complexity that the model attempts to encompass.
How do they go about determining that value?
The all-important question. The model covers all these variables, but with what accuracy do they make their assumptions...
The paper is accompanied by two supplemental appendices which are each bigger than the original paper, and could potentially be papers in their own right. One of these focuses on the basis of all the assumptions listed above, with references to historical literature. (I don't feel I'm in a position to evaluate it all).
One last thing, is there any consideration in the model to account for how much of the migratory input from one group to another would be stemmed by the loss of a line with a migratory ancestor at the root? In other words, is the effect of the migration permanent once it is introduced?
Not entirely clear on your question. Let me know if the details I listed above help clear up the issue for you on this one.
One thing I found interesting, from the original paper:
Interestingly, the MRCAs are nearly always found in eastern Asia. This is due to the proximity of this region to both Eurasia and either the remote Pacific islands or the Americas, allowing the MRCA's descendants to reach a few major world regions in a relatively short time.
This is the same result, I believe, that was found using a genetic model following the distribution of Y chromosome genotypes.
with much tentative skepticism
As you should approach any scientific paper or new model. Sorry if I was a bit testy earlier - it is frustrating to see work discredited without actual examination of the work. (Not saying you were the culprit...)

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pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 29 of 76 (329843)
07-08-2006 11:31 AM
Reply to: Message 25 by RAZD
07-08-2006 10:17 AM


genealogical, not genetic
There could be an MRCA from 7000 years ago, yet it might be that none of my genes are inherited via that chain.
I'm pretty sure that contradicts the concept of "Most Recent Common Ancestor" - but then I think the concept is bogus, that it is never a single organism, but a population of a species that all contribute.
An important point: The paper is solely modeling the genealogical MRCA, not a genetic MRCA. An ancestor in your genealogy need not contribute any genetic information to you as an individual, yet they were still in your family tree.
You mention that you believe an MRCP (population) could exist, but not an MRCA. How small could an MRCP be for you to find it acceptable? Say, one-hundred individuals?
Could one-hundred individuals have a single ancestor in common? (In other words, where and why does a limit come in to play?)
I'm short on time right now, but I'll try to respond to your longer post above - I also want to give you time to go over the paper, since it looked like you were still arguing against some incorrect assumptions in that post.

This message is a reply to:
 Message 25 by RAZD, posted 07-08-2006 10:17 AM RAZD has replied

Replies to this message:
 Message 33 by RAZD, posted 07-08-2006 12:39 PM pink sasquatch has not replied
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pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 53 of 76 (330453)
07-10-2006 2:45 PM
Reply to: Message 41 by RAZD
07-09-2006 1:36 PM


incorrect ideas about peer-review and ancestry
None of the math is in the {document\letter} -- we should also note that this is NOT a {presented peer reviewed paper} but a LETTER to the journal, and that there are different standards for peer review for letters compared to papers.
You are absolutely off the mark here. The "Letter" is the standard "paper" format for Nature, and the vast majority of Nature papers are "Letters". "Letter" simply describes the length and format, and "Letters" undergo rigorous peer-review identical to "Article" submissions. The current issue of Nature has thirteen Letters and only one Article.
If we are talking geneological ancestors we are talking genetic ancestors by definition of ancestor.
You seem to be stuck on a simple point here - you have genealogical ancestors whose genomes have contributed absolutely zero to your genome. It isn't a simple halving of a genome at each step.
You inherit 50% of your genome (in a simple sense) from your mother and 50% from your father. When you go back to grandparents however, you don't inherit 25% of your genome from each grandparent, due to variability in recombination and chromosome segregation. Potentially (though very improbably), one of your grandparents may have contributed zero to your genome.
In other words, it's possible 50% of your genome came from your mom's mom, and thus 0% from your mom's dad. However, your grandfather is still your genealogical ancestor.
Get it? Genealogical ancestry is not equivalent to genetic ancestry.

This message is a reply to:
 Message 41 by RAZD, posted 07-09-2006 1:36 PM RAZD has replied

Replies to this message:
 Message 54 by sfs, posted 07-10-2006 9:53 PM pink sasquatch has not replied
 Message 56 by RAZD, posted 07-10-2006 11:15 PM pink sasquatch has replied

  
pink sasquatch
Member (Idle past 6022 days)
Posts: 1567
Joined: 06-10-2004


Message 57 of 76 (330670)
07-10-2006 11:55 PM
Reply to: Message 56 by RAZD
07-10-2006 11:15 PM


still haven't read thoroughly, it seems...
If nothing else, a basic human pattern is for sexually active individuals to have several children with the same mate. Every additional child by the same parents cuts severely into the random equation. If we assume a minimum structured mating pattern holds over a 2 generation period then the MCRA 'advances' n/2=2/2=1 generation during those 2 generation periods.
Unless I'm reading something horribly wrong, it's already in the model:
After the first child, there is an 80% chance that the father of the previous child will also father the next one, thus simulating marriage.
It seems your criticism is not valid. They also include sex-based differences in marriage potential and fertility, as well as individual differences in mating success and fecundity.
It almost appears that they stopped evaluating the results when they got the 5000 year figure.
What specifically leads you to this accusation? Considering you didn't even read the methods to see that mating within subpopulations was non-random, I find it beyond the pale that you are suggesting fraud.
I also have a LOT of trouble with the "MRCA" terminology. You suggested MRCP, but nwr takes exception to that.
I merely suggested the acronym. I haven't made up my mind about the MRCA concept yet. You, on the other hand, had made up your mind and discounted the model before having even examined it.

This message is a reply to:
 Message 56 by RAZD, posted 07-10-2006 11:15 PM RAZD has replied

Replies to this message:
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