Appearence and tactics of early 5th century Saxons.

[Chariovalda]

All this, of course, is pending of further research in which the size of samples are increased.

Could someone explain to me how this research, which for all I know is done on living persons and not on ancient bone fragments, can really tell us something about peoples moving about in the past? I mean, if this is about very big groups, sure, I can guess that some statistics apply. But how on earth could we really tell if an influence took place in 300 BC or 1000 AD? Or am I right in thinking that these conclusions are reached with a book about migrations in the other hand?

Well, here I go. We have had these discussions before... 8)

In a nutshell:
Men have Y-chromosomes, which doesn't combine and which are only inherited in the male. This allows tracing direct male descent. Y-chromosomes can be grouped into haplogroups, which in turn can be subdivided into haplotypes and these can be subdivided again. The groups and types are defined by genetic markers that indicate past mutations, allowing the formation of a "genetic family tree".
Everybody has mitochondria, which are exclusively inherited through the mother. This allows a classification broadly similar to that of Y-chromosomes, and the construction of a family tree in the female line.

(My apologies if I describe this a bit superficially and crudely, but hey, I'm a historian by background, not a geneticist :wink: )

Anyway, the various different haplogroups and -types show distribution patterns that vary from region to region. They are the current end result of the past genetic history of the populations there. Distinct patterns have been found in various regions. For instance, when it comes to Y-chromosomes, populations in the western parts of Europe are surprisingly homogenous. One haplogroup, R1b, varies from over 90% in the Basque country to 80 to 90% in the "Celtic Fringe" (this is where all those media reports about "Irish and Welsh being close kin to Sardinians and Basques" come from) and about 70% in the far south of England and something about 50+% in our own little piece of swampish real estate. Eastward, the percentage quickly diminishes.
Faced with this, scientists had to explain this pattern. The most commonly accepted explanation is that we're dealing with a repopulation of western Europe after the last Ice Age, from a population that was genetically (at least on the Y chromosome level) surprisingly homogenous (suggesting, for instance, the existance of a "population bottleneck" at some time, severely limiting the number of Y-chromosome lineages present).

Anyway, other populations are more varied, suggesting a degree of mingling with other populations creating a more diverse Y-chromosome pattern. Among these, patterns can be discerned as well; some haplogroups and types are more common in some populations than others. Certain populations have a division of haplotypes that is very similar over a wide area, or share certain haplogroups / types that are rare elsewhere.
To a large degree, these represent the end results of demographic processes that are wholly or largely "invisible" to history (lacking adequate records) and archaeology. Interpreting modern (and, if available, ancient) genetic data in order to reconstruct a picture of these processes, has produced what Colin Renfrew has coined "archaeogenetics".

So far, so good. For some additional information I now refer you to:

[url:35ovu9jb]http://www.ucl.ac.uk/tcga/presentations/ASdemo/AS-26-11-03b.html[/url]
You don't have to agree with the conclusions of Weale (and I think you may have looked at it a few years ago), but it's a nice intro into the methodology.
As well as here:
[url:35ovu9jb]http://www.pnas.org/cgi/reprint/94/15/7719[/url]
A classic article by Luca Cavalli-Sforza, one of the fathers of historical genetics (or archaeogenetics, as Colin Renfrew calls it).
[url:35ovu9jb]http://www.pnas.org/cgi/reprint/98/9/4830[/url]
And an article by the ever-productive Lord himself