Received: by alpheratz.cpm.aca.mmu.ac.uk id NAA20627 (8.6.9/5.3[ref pg@gmsl.co.uk] for cpm.aca.mmu.ac.uk from fmb-majordomo@mmu.ac.uk); Thu, 21 Dec 2000 13:51:47 GMT Message-ID: <A4400389479FD3118C9400508B0FF2300411C3@DELTA.newhouse.akzonobel.nl> From: "Gatherer, D. (Derek)" <D.Gatherer@organon.nhe.akzonobel.nl> To: "'memetics@mmu.ac.uk'" <memetics@mmu.ac.uk> Subject: RE: Who knew genes could get mean? Date: Thu, 21 Dec 2000 14:45:32 +0100 X-Mailer: Internet Mail Service (5.5.2650.21) Content-Type: text/plain; charset="iso-8859-1" Sender: fmb-majordomo@mmu.ac.uk Precedence: bulk Reply-To: memetics@mmu.ac.uk
Vincent:
For example, I heard once that in the UK at least, you wouldn't
need to go back more than 150 years on average to find a common ancestor
between any two randomly selected people.
Derek:
I think it's a little longer than that, about 22 or so generations. But the
variance will be high, as its clear that most preindustrial revolution
communities were fairly isolated. These predictions are theoretical, and
based mostly on the calculation of the probability that 2 people don't
overlap in a set of 2powerN ancestors going back N generations. So where N
= 22, you have just over 4 miilion ancestors. If the generation time is 25
years on average, you're back to about 1450 when the population of mainland
Britain was about 4 or 5 million. So every possible ancestor is accounted
for. However, inbreeding within small villages, for instance, would mean
that the number of ancestors is far short of 2powerN, and one would have to
go back quite a bit further in order to account for all possible ancestors.
Relatedness can only really be tested empirically for those who have full
pedigrees, eg royalty. They do seem to be all related eg. see
http://www.dcs.hull.ac.uk/public/genealogy/royal/catalog.html, but they are
clearly a special case because of all the inbreeding. In genetic terms,
they might represent a sort of endogamous village, albeit one with rather
plusher mudhuts than most. So the claim often made eg see
http://www.dcs.hull.ac.uk/public/genealogy/royal/FAQ.html#Q4,
"It is not uncommon for people of British ancestry to descend from some
Royal or other. It has been said by some that all English descent from
Edward I and all Scots from Malcolm III. Therefore there is no particular
cachet in having any royal ancestors, but proving it is another matter
entirely!"
is a bit difficult to assess. If you believe the straight 2powerN argument,
then Edward I is a common ancestor of all Englishmen as he lived a good 6
generations before the 1450 threshold, but on the other hand if your
ancestors were entirely confined to a small village in the middle of
nowhere, then it would depend entirely on the rate at which exogenous genes
arrived in the population.
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