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From:
Subject: Re: Famous medieval DNA - the Plantagenet project
Date: Sat, 4 Aug 2007 17:42:03 +0100 (BST)
References: <mailman.44.1185962129.31452.gen-medieval@rootsweb.com><1185995710.722143.228160@e9g2000prf.googlegroups.com><mailman.87.1186043658.31452.gen-medieval@rootsweb.com><1186165128.988261.164360@e16g2000pri.googlegroups.com>
In-Reply-To: <1186165128.988261.164360@e16g2000pri.googlegroups.com>


> On Aug 2, 1:31 am, John Plant <> wrote:
>> taf wrote:

>> Apart from a couple, whose male lines both originated in south
>> Lincolnshire around 1800, these 9 have random haplotypes. This is
>> consistent with expectation for a surname that originated from a single
>> ancestor, since, in the centuries since then, about half of the lines
>> are expected to have a false paternity event (FPE) somewhere in the line
>> of descent (unfaithful wife, adoption, unmarried mother giving child her
>> own surname, etc). This phenomenon of FPEs is widely documented in
>> DNA-genealogy literature.
>
> The phenomenon has been widely discussed, but not widely documented.
> To document it, you actually have to show that people who 'should'
> have the same ancestor don't have the same type. All too often, though
> this is assumed rather than documented. Are any of yours documented
> FPEs?
>
> taf
>

Surely, no-one would deny that FPEs occur. No circular reasoning involved
in that. The question is how frequently?

For theoretical prediction, we can arrive only at a ball park figure.
Statistical estimates of FPE rates are based partly on studies of the
typical behaviour of modern populations. Rates of around 2% to 5% per
coupling are estimated. Taking the lower estimate, 2% per coupling
corresponds to once per 50 generations or around 50% per typical ancestral
line from a single-ancestor surname's male-line MRCA (though the MRCA may
be more recent than the originating single-ancestor of the surname). As a
simple estimate, around 50% of those with a single-ancestor surname can be
expected not to match.

This can be compared with experimental observation for the surname. If 50%
of the males with a given surname are found experimentally to match, this
indicates that the surname can be designated `single ancestor'.

A recent survey shows that relatively many surnames were thought by
one-name genealogists to be single-ancestor and have now been found by
Y-DNA testing to have *far* fewer than 50% in any one cluster if indeed
there are any clusters at all. This calls into doubt former assumptions by
many about their surname.

A smaller number of surnames were thought to be multi-origin and have been
found by Y-DNA testing to be `single-ancestor'. This can provide a basis
for reassessing the surname (as formally published to my knowledge for
Sykes and Plant).

Beyond this, I am not sure what you mean by (a) documenting the FPE
phenomenon; and, (b) documenting an individual FPE. If you mean: Can Y-DNA
evidence itself show that a particular apparent historical coupling within
a medieval line was in fact an FPE, the answer is no.

However, Y-DNA testing can show that two lines that were believed to have
a common paternal ancestor do not in fact. It can sometimes show that many
lines that were believed to have common paternity have led to matching
Y-DNA signatures for some but not for others (no doubt those with random
non-matching signatures have FPEs in their lines). It can disprove
document-based models of who does and who doesn't have an intact paternal
line from a common ancestor. It can supplement documentary evidence with
additional evidence (often with statistical probabilities rather than just
simple `sic et non' apparently yes or apparently no) and this can lead to
improved genealogical models. It cannot however do everything that
traditional genealogy can do.

Perhaps you already knew all this; but most people as yet seem to get
confused.

John






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