Re: Nazis, eh? I gotcher Nazis, right here...

http://mbe.oxfordjournals.org/cgi/content/full/19/7/1008

'Our results indicate the presence of a strong genetic barrier between Central England and North Wales and the virtual absence of a barrier between Central England and Friesland. Any attempt to explain these results in terms of demographic history and migration needs to encompass both these findings satisfactorily. The Central English-North Welsh barrier cannot be explained purely as a simple isolation-by-distance phenomenon because it contrasts strongly with the lack of evidence for a cline among the five widely separated English towns. Our findings are particularly striking, given the high resolution and rapid mutation rate of the Y chromosome haplotypes on which they are based. These allow genetic barriers, if they exist, to be clearly defined.

The best explanation for our findings is that the Anglo-Saxon cultural transition in Central England coincided with a mass immigration from the continent. Such an event would simultaneously explain both the high Central English-Frisian affinity and the low Central English-North Welsh affinity. If we use a rate of 0.1%, as observed over the past 25 years, to represent an extremely high value for continuous background migration between Central England and continental Europe, then we estimate that an Anglo-Saxon immigration event affecting 50%–100% of the Central English male gene pool at that time is required. We note, however, that our data do not allow us to distinguish an event that simply added to the indigenous Central English male gene pool from one where indigenous males were displaced elsewhere or one where indigenous males were reduced in number. Furthermore, although our models assume a single instantaneous migration event, we would also expect a more gradual process lasting several generations but still resulting in the same degree of admixture (a picture which may fit the historical data better [Härke 2002]) to produce very similar genetic patterns.

We accept that our data do not prove conclusively that an Anglo-Saxon mass migration event took place. If a background migration rate of 0.3% is allowed between Central England and Friesland, then the need for a mass migration event disappears. However, we note that this is an extremely high rate even by modern standards and would have to have been maintained continuously over thousands of years. A background migration rate of 0.3% would imply that one in six of today's Central English males descend from Frisians (or a population identical to Frisians) that emigrated to England after the Anglo-Saxon period and that an equal proportion of today's Frisians descend from English in a like manner. We also note that under a unidirectional gene flow model involving immigration into Central England only, the rate of background migration would then have to double to be at least 0.6% on a continuous basis.

It is also true that a mass migration event could have occurred outside the Anglo-Saxon migration period because the 95% confidence interval for a Central English-Frisian split extends as far back as 425 b.c. (if one allows a background migration rate of 0.1% and a generation time of 25 years). Archaeology and the testimony of Caesar combine to suggest an immigration of the Belgae, a Celtic tribe from northern Gaul, into central southern England (Hampshire and West Sussex) between 100 and 80 b.c. (Hawkes 1968Citation ; Cunliffe 1988Citation , pp. 147–149; Cunliffe 1991Citation , pp. 108–110). Furthermore, although Friesland lay outside the maximum extent of the Roman Empire, small numbers of Frisian mercenaries were recruited by the Romans and stationed as far north as Hadrian's Wall (Breeze and Dobson 1978Citation , pp. 139–140; Collingwood, Wright, and Tomlin 1995Citation , p. 501). However, most historians would see these movements, if they would acknowledge them at all, as preludes to post-Roman Anglo-Saxon migration, and it would be odd indeed to deny the latter while at the same time assigning an extremely large mass migration status to the former.

Finally, we accept that our inferences are based on population genetic analyses that assume a particular model of microsatellite evolution under selective neutrality and growth and that departures from these assumptions may influence our results. However, we note that the accuracy of the mutation model is diminished in importance by the small number of generations that would allow new mutations to accumulate since Anglo-Saxon times and also that any selective sweeps would also have to have been very recent in order to have influenced our conclusions greatly, especially because the effects of such sweeps would partly be accommodated by our model of exponential population growth. In addition, the estimates provided by BATWING for effective population sizes at the time of the Anglo-Saxon migration event are very small (table 1 ). Thus, a large amount of error caused by drift is already allowed for by our BATWING and Monte Carlo likelihood analyses. We do not presume an exact correspondence between real and effective population size dynamics or between the real population history of England, which has seen many different changes in size, and our simple model of exponential growth. However, we note that the posterior mode of the effective population growth rate per generation provided by BATWING (6.0%) almost exactly matches the real estimated population growth rate averaged over the past 1,500 years (Hatcher 1977Citation , pp. 1348–1530; Wrigley and Schofield 1989Citation , pp. 1541–1871; Härke 2002Citation ), whereas our 95% credible interval covers both the lower average growth rates of a.d. 500–1750 (approximately 3% per 25 years, albeit with large fluctuations) and the higher average growth rates of a.d. 1750–2000 (approximately 23% per 25 years).

Anglo-Saxon settlements and culture appeared throughout England but, importantly, did not extend into North Wales, where many of the original Celtic Britons living in England are thought to have fled (Kearney 1989Citation ; Davies 1993, 1999Citation ). Conflict between the Welsh and Anglo-Saxon kingdoms continued over a long period. Offa's Dyke (an earthwork barrier 240 km long) was constructed ca. a.d. 790 and provided a well-defined boundary between England and Wales. The linguistic, cultural, and political separation of the two regions lasted at least until a.d. 1282 when Edward I of England defeated the Welsh King Llywelyn II (Davies 1993Citation ). Our results suggest that this separation has also restricted male-mediated gene flow between the two regions over the past approximately 1500 years.

Comparisons of Central English and Norwegian haplotypes reveal no evidence of distinctive common signature haplotypes indicative of Viking origin, in contrast to Orcadian-Norwegian comparisons (Wilson et al. 2001)Citation . However, the Vikings who may have settled in East Anglia and the Midlands are thought to have been predominantly from Denmark, rather than Norway (Richards 2000)Citation . Previously published data suggest that the Danish have greater Y chromosome genetic affinity with the English than with the Norwegians (Malaspina et al. 2000; Rosser et al. 2000)Citation . However, the Danish-German border is believed to be another source location of the Anglo-Saxons (Kearney 1989Citation ; Davies 1999Citation ), so any Danish Viking influence on the English gene pool may prove difficult to distinguish from Anglo-Saxon influence. Further studies within Scandinavia and elsewhere are needed to resolve this issue.

This study shows that the Welsh border was more of a genetic barrier to Anglo-Saxon Y chromosome gene flow than the North Sea. Remarkably, we find that the resultant genetic differentiation is still discernible in the present day. These results indicate that a political boundary can be more important than a geophysical one in population genetic structuring and that informative patterns of genetic differentiation can be produced by migration events occurring within historical times.'
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