Archiver > GENEALOGY-DNA > 2002-01 > 1009974011

From: "David Andrews" <>
Subject: [DNA] Years per generation
Date: Wed, 2 Jan 2002 12:20:11 -0000
References: <a04310100b857d8b0e571@[]>

The reason for the disparity between the 20yr/gen and the 30-33yrs/gen is
very simple.

The 30-33yr figure is an oft quoted figure in genealogical circles and has
arisen from experience; many people researching their family history find
that, over 3 or 4 or more generations it works quite well (of course there
are occasional lines when it doesn't; that is what statistics is all about);
on average it works quite well. I read about it when I was setting out on my
researches, and was a bit 'sniffy' about it; but I must now confess that it
does seem to fit surpisingly well.

The 20yr figure is used by academic DNA reserarchers who are not confining
their interests to the recent past (hundreds of years) but right back to
pre-history (tens-of-thousands of years) over which most of the generations
will have been in more 'primative' societies where the breeding interval
probably started a little earlier and certainly ended a lot earlier than
they do in post AD1000 societies. In a primative agricultural or
hunter-gatherer society a breeding period of 15-ish-to-25-ish is quite
reasonably. To continue breeding into the mid-to-late thirties, as is common
in western society post AD1000, would be very rare in a primative

This whole debate has arisen from people thinking that the academic
DNA-researchers are interested in modern genealogy; they are not: their
interest is in genealogical and demographic changes that occur over
millennia and tens of millennia. They are not greatly, or mainly,
interested in recent genealogy, and hence do not use figures applicable to
that era.

The academic DNA-researchers are not doing all this for our benefit, and it
is disappointing that so many people don't seem to realise this.

Dave Andrews
Bristol UK

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