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A very interesting ethno-political map of Britain in AD 530 (above) based on the archaeological map below, the literary sources and other data (maps credit: Home Page for Howard Wiseman in Griffith Univ., maps added by periklisdeligiannis.wordpress.com)

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Republication from Nature.com

 

 

Stephan Schiffels, Wolfgang Haak, Pirita Paajanen,  Bastien Llamas, Elizabeth Popescu, Louise Loe, Rachel Clarke, Alice Lyons, Richard Mortimer, Duncan Sayer, Chris Tyler-Smith,   Alan Cooper & Richard Durbin

Nature Communications7,  Article number:10408  doi:10.1038/ncomms10408

 

British population history has been shaped by a series of immigrations, including the early Anglo-Saxon migrations after 400 CE. It remains an open question how these events affected the genetic composition of the current British population. Here, we present whole-genome sequences from 10 individuals excavated close to Cambridge in the East of England, ranging from the late Iron Age to the middle Anglo-Saxon period. By analysing shared rare variants with hundreds of modern samples from Britain and Europe, we estimate that on average the contemporary East English population derives 38% of its ancestry from Anglo-Saxon migrations. We gain further insight with a new method, rarecoal, which infers population history and identifies fine-scale genetic ancestry from rare variants. Using rarecoal we find that the Anglo-Saxon samples are closely related to modern Dutch and Danish populations, while the Iron Age samples share ancestors with multiple Northern European populations including Britain.

Introduction

Within the last 2,000 years alone, the British Isles have received multiple well-documented immigrations. These include military invasions and settlement by the Romans in the first century CE, peoples from the North Sea coast of Europe collectively known as the Anglo-Saxons between ca. 400 and 650 CE (Fig. 1a), Scandinavians during the late Saxon ‘Viking period’ 800–1,000 CE and the Normans in 1,066 CE (ref. 1). These events, along with prior and subsequent population movements, have led to a complex ancestry of the current British population. Although there is only a slight genetic cline from north to south at a coarse level2, 3, recent analyses have revealed considerable fine-scale genetic structure in the Northern and Western parts of Great Britain, alongside striking homogeneity in Southern and Eastern England4 in the regions where archaeologists identify early Anglo-Saxon artifacts, cemeteries and communities. A variety of estimates of the fraction of Anglo-Saxon genetic ancestry in England have been given5, 6, 7, 8, with the recent fine structure analysis suggesting most likely 10–40% (ref. 4).

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Figure 1: Geographic and temporal context of the samples used in this study.

Geographic and temporal context of the samples used in this study.

(a) Anglo-Saxon migration routes of people from the continental coast, as reconstructed from historical and archaeological sources. (b) The ancient samples used in this study were excavated at three archaeological sites in East England: Hinxton, Oakington and Linton. The towns Cambridge and Saffron Walden are also shown (black circles). Background green/brown shades indicate altitude. The colours of the four sample match the ones in c and Fig. 2. (c) The 10 ancient samples belong to three age groups. The sample from Linton and two samples from Hinxton are from the late Iron Age, the four Oakington samples from the early Anglo-Saxon period and three Hinxton samples are from the middle Anglo-Saxon period.

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However, even large-scale analyses of present-day data provide only weak evidence of the Anglo-Saxon migration impact, mainly for two reasons. First, estimating the impact of historical migrations from present-day genetic data alone is challenging, because both the state of the indigenous population before the migration as well as the genetic make up of the immigrants are unknown and have to be estimated simultaneously from present-day data. Second, if the source population is genetically close to the indigenous population, migrations are hard to quantify due to the challenge in detecting small genetic differences. This is particularly true for the case of the Anglo-Saxon migrations in Britain, given the close genetic relationships across Europe

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