The genetic structures of past human populations are obscured by recent migrations and expansions and have been observed only indirectly by inference from modern samples. However, the unique link between a heritable cultural marker, the patrilineal surname, and a genetic marker, the Y chromosome, provides a means to target sets of modern individuals that might resemble populations at the time of surname establishment. As a test case, we studied samples from the Wirral Peninsula and West Lancashire, in northwest England. Place-names and archaeology show clear evidence of a past Viking presence, but heavy immigration and population growth since the industrial revolution are likely to have weakened the genetic signal of a 1,000-year-old Scandinavian contribution. Samples ascertained on the basis of 2 generations of residence were compared with independent samples based on known ancestry in the region plus the possession of a surname known from historical records to have been present there in medieval times. The Y-chromosomal haplotypes of these 2 sets of samples are significantly different, and in admixture analyses, the surname-ascertained samples show markedly greater Scandinavian ancestry proportions, supporting the idea that northwest England was once heavily populated by Scandinavian settlers. The method of historical surname-based ascertainment promises to allow investigation of the influence of migration and drift over the last few centuries in changing the population structure of Britain and will have general utility in other regions where surnames are patrilineal and suitable historical records survive.
A useful test case to evaluate the potential of surname-based ascertainment is provided by the 1,000-year-old Viking settlement of the British Isles. The Viking age of raiding, exploration, trading, and colonization began in the late eighth century, with a series of attacks on the coasts of Britain, Ireland, and France. In England, a shift from raiding to permanent settlement began after AD 865. The modern consensus has moved from the earlier view of a mass migration of Viking settlers to a more geographically variable and gradual process, with much assimilation of local culture, under the administration of a Scandinavian elite (Richards 2004). Even though Viking rule in England came to an end nearly 1,000 years ago and the settlers were soon integrated linguistically and culturally, abundant evidence of Scandinavian influence remains today. Important archaeological findings exist, but the most striking evidence is linguistic and onomastic—many words in Standard English and in local dialects, and many place-names, are of Scandinavian origin. In some areas of English counties that formed part of the Danelaw (fig. 1), the region under the administrative control of the Vikings from the late ninth century, up to 70% of major place-names are in this category, with endings such as “-by” and “-thorp(e).”
In one version of events, Vikings of Norwegian origin, under their leader Ingimund, arrived in the region in AD 902 after having been expelled from Dublin. Æthelflæd, Lady of the Mercians, granted them land in north Wirral, where they settled (Wainwright 1942, 1948, 1975). More complex models have also been proposed, based on place-names analysis, including elements of migration from the Isle of Man as well as Dublin (Fellows-Jensen 1992). Specific historical evidence for the migration of Vikings into West Lancashire is lacking, although place-names and archaeological evidence clearly demonstrate that this occurred.
Widespread migration and population expansion in recent centuries present a particular problem in genetic analyses of mainland regions of Britain. The Wirral experienced a major influx of people since the medieval period, its population growing over 70-fold between 1545 and 1921 (Roberts 2002)—almost 10 times the national average increase. In conventional sampling strategies, where 2 generations of residence in an area are sufficient to qualify a DNA donor for participation in a study, the signal of Viking influence is likely to be weakened by the noise of more recent population movement
Where comparisons can be made, the proportions of Scandinavian admixture that we estimate differ somewhat from those seen in a previous study (Goodacre et al. 2005): for Shetland, we observe 41% Scandinavian ancestry compared with the previously published figure of 44% and the corresponding figures for Orkney are 50% compared with 31%. Such differences may reflect sampling variance or differences in the compositions of the parental and hybrid samples and in the marker resolution—we used greater numbers of both binary markers and microsatellites. Note that direct comparisons with the study from which we draw our comparative data (Capelli et al. 2003) are problematic because it used a different admixture method and considered admixture between a Norwegian sample and a sample chosen to represent Anglo-Saxons. The lowest proportions of Scandinavian admixture among our samples are seen in Llangefni and Mid-Cheshire, at 10% and 21%, respectively. In agreement with previous results (Capelli et al. 2003), a higher proportion (39%) is seen in the Isle of Man, where there is a known history of Viking presence, and Penrith (37%), which shows Scandinavian dialect influence (Reaney 1927). The modern samples from Wirral and West Lancashire both show 38% Scandinavian admixture, markedly higher than the nearby sample from Mid-Cheshire (21%). This is consistent with the historical and place-name evidence for greater Viking presence in Wirral and West Lancashire than in Mid-Cheshire.
The medieval sample from West Lancashire shows an increased proportion (51 ± 4%) of Scandinavian ancestry compared with its modern counterpart (38 ± 4%); the equivalent values for Wirral are 47 ± 5% and 38 ± 3%. These differences, revealed by our different sampling strategies, are likely to reflect a change in haplotype frequencies due to postmedieval immigration and are supported by genetic distances (FST) between the Norwegian sample and the Wirral and West Lancashire samples. FST between Norwegians and the West Lancashire modern sample is 0.130, whereas the value for the medieval sample is only 0.069; corresponding values for the Wirral samples are 0.162 and 0.096.
The surnames that we used to ascertain the medieval samples belong to a wide range of frequencies—from “Otty,” with only 146 bearers in 1998 (www.spatial-literacy.org/UCLnames/) to “Brown,” with 242,765 (supplementary table, Supplementary Material online). The more frequent names are likely to have had multiple founders and are relatively widespread in Britain and so may provide less reliable links to medieval presence in the specific regions under study. To address this, we subsampled from the 2 medieval samples by removing surnames with frequencies of greater than 20,000 (supplementary table, Supplementary Material online), resulting in reduced sample sizes of 26 and 30 for Wirral and West Lancashire, respectively. We then repeated the admixture analysis. In both cases, the proportions of Scandinavian admixture in the subsampled medieval populations increased further compared with the original medieval samples: admixture proportions in the modern and medieval subsampled Wirral populations are now 38 ± 3% compared with 51 ± 6% and the corresponding values for West Lancashire are 38 ± 4% compared with 53 ± 5%.
There you go dog..................
