Archiver > GENEALOGY-DNA > 2005-06 > 1118085113

From: (John Chandler)
Subject: Re: [DNA] Lancaster Project
Date: Mon, 6 Jun 2005 15:11:53 -0400 (EDT)
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Andrew wrote:
> Wouldn't this mean that you are saying that the null hypothesis should be
> that a haplotype with a particular surname will be *different* from modal,
> and not just for example 50% likely to be different?

Quite right. Consider a haplogroup that is 10,000 years old. Call that
400 generations. The probability that a descendant line has had no
mutations at all over that time span on 25 markers is about 1e-10.

> John:
> The question as stated has a simple answer: the likelihood that your
> speculative link is proven is exactly zero.
> That's a rather high degree of certainty. Do you mean 50%?

It is indeed a high degree of certainty. You have certainly not proven
any link. I generally mean what I say.

> Obviously you *can* say that the existance of a link is proven or proven to
> be likely, and *not* be understood to be claiming to know what the link is.

Wrong. We may be dealing in genetics, but this is still genealogy. A
link is a specific relationship. What you have is merely a vague
feeling that there "must" be a common ancestor somewhere and at some
time, if only you could find evidence. Go look for evidence, and you
may then be able to prove a link, but not until then. Note that the
probability of a common ancestor rises monotonicaly to the limit of
100% if you just push back the time window enough. Therefore, by your
understanding of a "proven link" everyone already has it, and the
discussion is moot.

> Clearly in fact this is the whole basis of why people even discuss
> comparisons of people with different surnames - because they are considering
> looking for evidence such as paper trails in a particular direction.

Mostly, the reason they discuss it is desperation -- the lack of
anything else concrete to discuss. In practical terms, it's a very
difficult quest and rendered even trickier by the alternative
possibilities of non-paternal events all along the way or simple
lineages that join before the availability of documentation.

John Chandler

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