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  #21  
Old 12 November 2017, 12:22 PM
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BrianB, FWIW, I think you're right to bite your tongue, so long as your mother's belief in family trees isn't causing any harm.

ETA: Some clarification, though: primary records like birth and death certificates, census records, etc, are historical records, right? The people I know who practice genealogy as a hobby work with those records; they don't find some family tree prepared by someone else and take it as fact (although they may use it as a starting point).
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  #22  
Old 12 November 2017, 01:32 PM
dfresh dfresh is offline
 
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Lainie, those are good records to work from. The family trees are pretty much guesswork a lot of times, however.
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  #23  
Old 12 November 2017, 02:38 PM
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Quote:
Originally Posted by Cervus View Post
(But according to the book I am also related to everyone who ever existed, so...)
Well, to be fair, that's true.

If you go back far enough, everybody is related to everybody else.

(Admittedly, this is rarely what people who brag about distant relationships are bragging about. They tend if anything to be annoyed if it's pointed out.)
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  #24  
Old 12 November 2017, 10:58 PM
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Quote:
Originally Posted by thorny locust View Post
Well, to be fair, that's true.

If you go back far enough, everybody is related to everybody else.

(Admittedly, this is rarely what people who brag about distant relationships are bragging about. They tend if anything to be annoyed if it's pointed out.)
Isn’t that what the call ‘population collapse’. We have 2 parents, 4 grandparents, 8 great-grandparents, ad nauseum. About 20 generations back and you’re talking about 1,000,000 people you are descended from who were alive in that generation. Very quickly it gets to the point where the number of supposed ancestors exceeds the total population at the time, especially if it is in a geographically isolated region.
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  #25  
Old 12 November 2017, 11:31 PM
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There is also the fact that it's been determined both genetically and by mathematical simulation that everyone on the planet almost certainly shared at least one common ancestor who lived as recently as 3,500 years ago. (This date would be several thousand years earlier at least if not for the fact that there are no remaining natives of Tasmania who do not have some non-Tasmanian ancestry.)
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  #26  
Old 13 November 2017, 04:44 PM
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Quote:
Originally Posted by Lainie View Post
BrianB, FWIW, I think you're right to bite your tongue, so long as your mother's belief in family trees isn't causing any harm.

ETA: Some clarification, though: primary records like birth and death certificates, census records, etc, are historical records, right? The people I know who practice genealogy as a hobby work with those records; they don't find some family tree prepared by someone else and take it as fact (although they may use it as a starting point).
Lainie, you asked the question I was tempted to ask. Thank you.

Quote:
Originally Posted by dfresh View Post
Lainie, those are good records to work from. The family trees are pretty much guesswork a lot of times, however.
Everything on my family tree is either backed by a primary record (birth, death, census, baptism) or specifically marked as questionable. There are only a few lines that go back more than 4 generations. My grandmother spent many days/months/years looking through records to create it.
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  #27  
Old 13 November 2017, 05:26 PM
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One of the companies has really annoying commercials about people discovering they're really from one area instead of what the family history says. They then proceed to adopt the cultural trappings of their "real" ancestry.

I'm pleased to know these companies are full of it.

Being that part of my family is Irish Catholic, even primary records aren't too useful. It's really tough telling all those Marys apart.
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  #28  
Old 13 November 2017, 06:08 PM
jimmy101_again jimmy101_again is offline
 
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The Philly Inquirer article really isn't very useful. If you are going to say something isn't accurate you really should give an estimate of how inaccurate it is and how that was determined. A quote from an anthropologist isn't particularly convincing.

Besides, in it's most common and important use of determination of parenthood "determining ancestry" is considered to be 100% accurate and basically legally irrefutable.

So the ancestry craze might be based on bad science but the science of the article is certainly no better.
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  #29  
Old 13 November 2017, 09:56 PM
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Quote:
Originally Posted by Seaboe Muffinchucker View Post
Two friends (a brother & sister) had this done. The results came back more or less as expected for immediate ancestry, but the proportions were different. That actually made sense to me, because there are genetic differences between siblings.
I think you're referring to my husband and his sister, or at least the facts match. The strange thing is that their father's genealogy is 100% Sicilian; their mother's is 100% Welsh. The siblings look (to the untrained eye) absolutely dissimilar. He looks very much like their Welsh grandfather. She looks very much like their Sicilian grandmother. His percentage of Sicilian DNA is much higher than hers; her percentage of Welsh DNA is much higher than his. Go figure.

And as I was the one that bought the Ancestry kits and had them do the testing, I should add: I got the kits to assist in researching their family trees, not to figure out their "country of origin" as it were. If you have a tree on Ancestry, and match your DNA kit to your name in that tree, they show your DNA matches -- people who are likely to be related to you based on their DNA, and if those individuals also have an Ancestry tree it can help your genealogical research. In my husband's family, I was hoping it would get me past some roadblocks (one ancestress was abandoned as an infant on the church steps, for example -- family legend is that she was the illegitimate child of some local nobleman, of course), but while they are getting matches, it looks like most of those people have experienced the same roadblocks. I, on the other hand, was able to confirm one branch of my tree that I was pretty sure was correct, but that I could not prove with the documents available to me.

Last edited by Tootsie Plunkette; 13 November 2017 at 10:05 PM.
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  #30  
Old 13 November 2017, 11:54 PM
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Quote:
Originally Posted by jimmy101_again View Post
Besides, in it's most common and important use of determination of parenthood "determining ancestry" is considered to be 100% accurate and basically legally irrefutable.
Cite please.
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  #31  
Old 14 November 2017, 06:07 PM
jimmy101_again jimmy101_again is offline
 
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Quote:
Originally Posted by ganzfeld View Post
Cite please.
Uh, pretty much every paternity court in the US. Plus, of course, Jerry Springer.

There is no viable way to challenge a DNA based negative maternity or paternity test in court. (Really the only challenged would be to challenge that the test was done incorrectly, the sample was contaminated, ...) Positive test are sometimes challenged, but those challenges aren't usually successful.
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  #32  
Old 14 November 2017, 06:24 PM
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So it is legally 100% accurate and irrefutable except when it isn't?

And it might be considered that way, but it certainly isn't in all cases. The Atlantic has a good article about the potential scientific issues with DNA testing (about halfway down).

ETA: The article is mostly about DNA matching for criminal prosecution but it talks about issues with general DNA testing such as a murder case where matching samples from 40 different crime scenes turned out to be matching a worker in the factory that made the DNA swabs.
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  #33  
Old 14 November 2017, 06:48 PM
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Quote:
Originally Posted by GenYus234 View Post
And it might be considered that way, but it certainly isn't in all cases. The Atlantic has a good article about the potential scientific issues with DNA testing (about halfway down).
Bold emphasis mine. I would semantically argue that it is more a procedural issue than a scientific issue. Reading the article, it does not seem to be saying that the science of DNA matching is unsound or incorrect. But, rather, that is is not simple or quick and that these difficulties and challenges are not being presented to Juries, or other's making decisions based on DNA evidence.

It seems to say that within certain constraints, quality of samples, practices and procedures followed, etc., the matches are very high quality. But a lot of cases are not such, especially the quality of samples and the way sample data is being stored and compared.
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  #34  
Old 14 November 2017, 09:03 PM
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In this case, I don't think asking for a cite to support the claim should be taken rhetorically or merely as an interjection. This issue is not an obscure question of law or the bio industry that no one has ever written on.
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  #35  
Old 14 November 2017, 09:23 PM
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Quote:
Originally Posted by iskinner View Post
I would semantically argue that it is more a procedural issue than a scientific issue. Reading the article, it does not seem to be saying that the science of DNA matching is unsound or incorrect.
I would agree that the vast majority of issues are procedural, but the article touches on the science issues too. Specifically the fact that DNA matching is not done on the entirety of a single strand of DNA, but on specific alleles found in the entire sample. This puts the burden of reliability on the purity of the sample. As a contrast, gas chromatography can prove or disprove the presence of a specific element no matter how pure or impure the sample.
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  #36  
Old 14 November 2017, 10:50 PM
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Not disagreeing with you Genyus but just to add:

Even though gas chromatography can be far far more precise than DNA paternity testing, it's still a matter of probabilities.

Last edited by ganzfeld; 14 November 2017 at 11:02 PM.
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  #37  
Old 15 November 2017, 03:17 AM
jimmy101_again jimmy101_again is offline
 
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Everything is a matter of probability. The law is based on probabilities even if people don't look at it that way. "Beyond a reasonable doubt" is a probability statement, not a statement of fact.
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  #38  
Old 15 November 2017, 03:26 AM
jimmy101_again jimmy101_again is offline
 
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Quote:
Originally Posted by GenYus234 View Post
So it is legally 100% accurate and irrefutable except when it isn't?.
Yes. Indeed if you read the legal literature nad court cases the ability to prove non-parent hood is generally considered to be scientifically irrefutable. It can only be refuted on procedural grounds but EVERYTHING in a legal case is refutable on those grounds.

The reliability to prove parenthood is almost as strong and I would argue that even that is stronger than virtually anything else in a trial. Eyewitnesses are notoriously unreliable. Confessions are notorious unreliable. Even finger prints are no longer considered to be foolproof, like they once were, because there is a fair amount of subjectivity in fingerprint matching.
Fingerprint failure rate roughly 0.1% in this study http://www.pnas.org/content/108/19/7733

Also, https://www.pbs.org/wgbh/frontline/a...so-scientific/
Teeth marks, hair, even fingerprints are considered less reliable than DNA.
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  #39  
Old 15 November 2017, 05:55 AM
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None of those address, never mind support, your claim:
Quote:
Originally Posted by jimmy101_again View Post
Besides, in it's most common and important use of determination of parenthood "determining ancestry" is considered to be 100% accurate and basically legally irrefutable.
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  #40  
Old 15 November 2017, 08:05 AM
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The find-your-ancestry companies use much cheaper and less accurate tests than what forensic labs or paternity tests do. It's like the difference between a cheap pair of X2 magnification binoculars and a major observatory. Both let you see Jupiter, but there's a serious difference in the quality of the image.
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