y chromosome evidence for anglo-saxon mass migration
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Y Chromosome Evidence for Anglo-Saxon Mass MigrationTRANSCRIPT
1008
Mol. Biol. Evol. 19(7):1008–1021. 2002q 2002 by the Society for Molecular Biology and Evolution. ISSN: 0737-4038
Y Chromosome Evidence for Anglo-Saxon Mass Migration
Michael E. Weale,*1 Deborah A. Weiss,†1 Rolf F. Jager,*‡ Neil Bradman,* andMark G. Thomas**The Centre for Genetic Anthropology, Departments of Biology and Anthropology, University College London,University of London; †Department of Anthropology, University of California, Davis; and ‡Faculteit Biologie,Vrije Universiteit, Amsterdam, The Netherlands
British history contains several periods of major cultural change. It remains controversial as to how much theseperiods coincided with substantial immigration from continental Europe, even for those that occurred most recently.In this study, we examine genetic data for evidence of male immigration at particular times into Central Englandand North Wales. To do this, we used 12 biallelic polymorphisms and six microsatellite markers to define high-resolution Y chromosome haplotypes in a sample of 313 males from seven towns located along an east-west transectfrom East Anglia to North Wales. The Central English towns were genetically very similar, whereas the two NorthWelsh towns differed significantly both from each other and from the Central English towns. When we comparedour data with an additional 177 samples collected in Friesland and Norway, we found that the Central English andFrisian samples were statistically indistinguishable. Using novel population genetic models that incorporate bothmass migration and continuous gene flow, we conclude that these striking patterns are best explained by a substantialmigration of Anglo-Saxon Y chromosomes into Central England (contributing 50%–100% to the gene pool at thattime) but not into North Wales.
Introduction
Following depopulation during the last glacial max-imum and subsequent resettlement by hunter-gatherersca. 7000 B.C., the history of Britain has been marked bya series of cultural transitions. These include the ap-pearance of sedentary agricultural communities (theNeolithic transition) (ca. 4000 B.C.), the arrival andspread of Late Bronze-Iron Age and Celtic material cul-ture (ca. 1000–100 B.C.), Roman occupation and influ-ence (A.D. 43–410), the rise of Anglo-Saxon languageand culture (ca. A.D. 400–800), Viking invasions andinfluence (ca. . 800–1000), and the Norman Conquest(A.D. 1066) (Kearney 1989; Hunter and Ralson 1998;Davies 1999).
The use of migration as an explanation for culturaltransitions has varied greatly over the past 100 years andremains controversial (Clark 1966; Chapman 1997; Bur-meister 2000; Shennan 2000). Before the 1960s, ar-chaeological evidence for cultural change (such aschanges in pottery type) was often interpreted as primafacie evidence for substantial immigration. The proces-sual school or New Archaeology that emerged in the1960s and 1970s rejected this view, arguing firstly thatthe adoption of new cultures could occur through tradeor by the influx of a small ruling elite with minimal orno impact on the gene pool (the ‘‘elite dominance’’model of Renfrew [1987]) and secondly that if no pos-itive evidence for migration could be found then expla-nations based on non–migrational internal forces were
1 Both these authors contributed equally to this work.
Key words: Y chromosome, unique event polymorphisms, micro-satellite haplotypes, British population history, genetic anthropology,population genetic models.
Address for correspondence and reprints: Michael Weale, TheCentre for Genetic Anthropology, Departments of Biology and An-thropology, University College London, University of London, DarwinBuilding, Gower Street, London WC1E 6BT, United Kingdom. E-mail:[email protected].
more parsimonious and therefore preferable (Adams1968; Adams, Van Gerven, and Levy 1978). More re-cently, this antimigrationist stance has been questioned(Anthony 1990; Harke 1998) and migrational modelsreconsidered (e.g., Chapman and Hamerow 1997; Bur-meister 2000).
These changes in archaeological opinion have hada particular impact on interpretations of cultural transi-tions in Britain (Clark 1966). Because of its geograph-ical location on the northwestern edge of Europe, mi-grations and invasions from the continental mainlandwere once considered to be the obvious explanation forcultural transition (e.g., Hawkes and Hawkes 1942). To-day, cultural changes before the Roman invasion, whichare for the most part lacking in historical records, areno longer interpreted as automatically implying migra-tion, and for these changes the role of migration remainsunresolved. For cultural transitions after the Roman in-vasion, historical records argue against large migrationscoinciding with either Roman occupation or the NormanConquest, and the prevailing view is therefore that theselater events represent examples of elite dominance(Kearney 1989; Davies 1999). Historical and archaeo-logical research argue for some degree of Viking settle-ment in both East Anglia and the Midlands in the 9thcentury A.D. but against a substantial displacement ofthe existing people during this period (Richards 2000).
Today, the most hotly debated of all the Britishcultural transitions is the role of migration in the rela-tively sudden and drastic change from Romano-Britainto Anglo-Saxon Britain (Hamerow 1997; Burmeister2000). This transition was once widely accepted as pro-viding clear evidence for a mass migration from conti-nental Europe and the near-complete replacement of theindigenous population in England (Leeds 1954; Myres1986). Stories of migration are included in the writingsof Gildas (ca. A.D. 540) and Bede (A.D. 731) and hintedat in Anglo-Saxon sagas, such as Beowulf (Davies1999). Archaeological evidence confirmed a rapid rise
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of continental culture in England (Esmonde-Cleary1993) and suggested a contemporaneous desertion ofcontinental Germanic settlements. More recently, how-ever, authors have questioned the evidence for large-scale immigration (Crawford 1997; Hamerow 1997) andcontinental emigration (Nasman 1988; Petersen 1991)and emphasized the continuity of the Romano-Britishpopulation in England. The sudden change to an Anglo-Saxon culture has been attributed instead to rapid ac-culturation and indigenous developments, with only asmall number of Germanic immigrants (perhaps a malemilitary elite) settling in Britain (Arnold 1984; Hodges1989; Higham 1992). The contribution of Anglo-Saxonimmigration to the modern English gene pool thus re-mains uncertain.
Genetic data comprise an obvious source of infor-mation to help resolve these issues. Previous studies ex-amining biological variation in Britain have identifiedvarious patterns of genetic variation. These include stud-ies on blood groups (Bodmer 1993; Mascie-Taylor andLasker 1996), serum proteins and isoenzymes (Cart-wright, Hargreaves, and Sunderland 1977; Mastana etal. 1993), HLA genes (Papiha, Duggan Keen, and Rodg-er 1985; Bodmer 1993), and multiple classical geneticmarkers (Falsetti and Sokol 1993; Cavalli-Sforza, Men-ozzi, and Piazza 1994; Mastana and Sokol 1998), aswell as on patterns of disease incidence, such as phe-nylketonuria (Tyfield, Osborn, and Holton 1997), mul-tiple sclerosis (Poser 1994), skin cancer (Long, Darke,and Marks 1998), and haemochromatosis (Merryweath-er-Clarke et al. 1997). These data have been interpretedas reflecting historical migrations and settlement pat-terns, but formal testing of alternative migratory modelshas not been attempted.
The non–recombining portion of the Y chromo-some and the mitochondrial genome are useful sourcesof data because they provide exceptionally detailedhigh-resolution haplotypes, allowing fine definition ofthe underlying gene genealogies. The Y chromosome,which is much larger, is particularly useful because ithas many slowly mutating biallelic markers to help re-solve genealogical clades as well as rapidly mutatingmicrosatellite markers to aid in the dating of very recentevents (Thomas et al. 1998; Kayser et al. 2001). Theextra information provided by these high-resolution hap-lotypes facilitates the fitting of population genetic mod-els. Although the resulting demographic inferences arebased on only a single locus, increasing the effects ofevolutionary variance derived from chance differencesin the genealogy, such systems are still useful becausethey are the only ones that allow sex-specific demo-graphic inferences to be made.
Previous studies of mtDNA and Y chromosomevariation across Europe have reported evidence of Pa-leolithic and Neolithic expansions reflected in large-scale clines (Torroni et al. 1998; Casalotti et al. 1999;Hill, Jobling, and Bradley 2000; Malaspina et al. 2000;Richards et al. 2000; Rosser et al. 2000; Semino et al.2000; Simoni et al. 2000), but these studies did not con-sider the effects of historical migrations on more localpatterns of genetic variation. Helgason et al. (2000) ex-
amined Y chromosome and mtDNA variation in themodern Icelandic population to assess the relative pro-portions of Scandinavian and Celtic ancestry stemmingfrom historical migrations, whereas Wilson et al. (2001)compared Y chromosome, X chromosome, and mtDNAvariation in eight population samples (including theLlangefni, Norway, and Friesland samples reportedhere) to investigate genetic changes associated with cul-tural transitions in North Wales and Orkney, two areasat the fringes of the British Isles. Through a comparisonof signature haplotypes, Wilson et al. (2001) found ev-idence for Celtic male ancestry in the North Welsh and/or both Celtic and Scandinavian (Viking) male ancestryin the modern Orcadian population. Further comparisonsof these British samples with Basque data suggested thatthe male Celtic genetic component was Paleolithic inorigin, and therefore, that subsequent cultural transitionsin North Wales were not associated with substantial in-coming male gene flow. However, the study of Wilsonet al. did not directly address the effects of cultural tran-sitions in other areas of Britain.
This study is the first to analyze data from an east-west transect across Central England and North Walesto evaluate evidence of male population migration undera wide range of flexible population genetic models.Samples were collected in seven towns along this tran-sect, and a combination of slowly evolving biallelicmarkers (so-called Unique Event Polymorphisms orUEPs) and rapidly evolving microsatellites on the Ychromosome were typed to look for evidence of localor small-scale genetic transitions. We compared the datawith samples from Friesland and Norway to look forevidence of male immigration from the continent. In ad-dition to comparing signature haplotypes among popu-lation samples, we applied novel model-based methodsto make inferences about both the possible timing andextent of male continental migration into CentralEngland.
Materials and MethodsPopulation Samples and Genotyping
Buccal swabs were collected from 313 males in theBritish towns of North Walsham, Fakenham, Bourne,Southwell, Ashbourne, Abergele, and Llangefni (fig. 1).These towns were selected because they lie approxi-mately 50 km apart along an east-west transect of Brit-ain and are long established market towns (mentionedin the Domesday Book of A.D. 1086 with current pop-ulations of 5,000–10,000) that are less likely to be in-fluenced by recent migration than large cities (Pooleyand Turnbull 1998). We apply the labels ‘‘East Anglia’’to the North Walsham and Fakenham samples, ‘‘Mid-lands’’ to the Bourne, Southwell, and Ashbourne sam-ples, ‘‘North Wales’’ to the Abergele and Llangefni sam-ples, and ‘‘Central England’’ to the combined Midlandsand East Anglia samples, although these labels are forconvenience and only designate the general geographi-cal area of these samples. Samples were acquired if boththe donor and the donor’s paternal grandfather wereborn within 30 km of one of these market towns. For
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FIG. 1.—(a) Map of Britain and neighboring area. (b) Enlarge-ment showing towns within Britain along east-west transect.
FIG. 2.—Y chromosome haplogroup network defined by the 11UEP markers used in this study following a nomenclature modifiedfrom Rosser et al. (2000) and Weale et al. (2001). The root has beendeduced by comparison with other great ape species (Underhill et al.[2000]; P. Underhill, personal communication for position ofSRY10831). Shading indicates haplogroups observed in this study.
comparison, we also collected DNA samples from 94males in Friesland (northern Netherlands) and 83 malesin Norway, two nearby locations with different roles inBritain’s immigration history. Friesland is thought to beone of the source locations for Anglo-Saxon immigra-tion both because of its geographical location and be-cause Frisian is considered to be the closest extant lan-guage to Old English (Nielsen 1985). Norway representsone source of the Viking invaders. Samples were col-lected anonymously, and informed consent was obtainedfrom all individuals before samples were taken.
Standard phenol-chloroform DNA extractions wereperformed. Six microsatellites (DYS19, DYS388,DYS390, DYS391, DYS392, DYS393) and 11 of thebiallelic UEP markers (92R7, M9, M13, M17, M20,SRY1465, SRY4064, SRY10831, sY81, Tat, YAP)were typed and analyzed, as described by Thomas,Bradman, and Flinn (1999). One additional UEP marker,12f2, was typed, as described by Rosser et al. (2000).Microsatellite repeat sizes were assigned according tothe nomenclature of Kayser et al. (1997). Haplogroupswere defined by the 12 UEP markers according to anomenclature modified from Rosser et al. (2000) andWeale et al. (2001) and are presented in figure 2. Thecorrespondence between this nomenclature and that pro-posed by the Y Chromosome Consortium (2002) is asfollows: hg1 5 P*(xR1a), hg2 5 BR*(xDE,JR), hg3 5R1a1, hg4 5 DE*(xE), hg7 5 A3b2, hg8 5 E3a, hg95 J, hg16 5 N3, hg20 5 O2b, hg21 5 E*(xE3a), hg265 K*(xL,N3,O2b,P), hg28 5 L, hg29 5 R1a*, hg37 5Y*(xBR,A3b2).
Statistical and Population Genetic Analysis
We tested for significant population differentiationusing the Exact Test for Population Differentiation ofRaymond and Rousset (1995). Unbiased genetic diver-sity, h, and its standard error were calculated using theformulae given by Nei (1987, pp. 178–180). We quan-
tified patterns of genetic differentiation using the geneticdistance measures FST and RST estimated from analysisof molecular variance (AMOVA) FST values (Reynolds,Weir, and Cockerham 1983; Michalakis and Excoffier1996). Confidence intervals for these statistics were con-structed using bootstrap estimates of standard errorsbased on resampling haplotypes according to observedpopulation frequencies. We visualized patterns of ge-netic differentiation using principal coordinates analysisperformed on a similarity matrix calculated as 1 2 RST.Values along the main diagonal of the similarity matrix,representing the similarity of each population sample toitself, were calculated from the estimated genetic dis-tance between two copies of the same population sample(for FST-based FST and RST values, the resulting self-similarity values simplify to n/(n 2 1), where n is thesample size).
We explored population genetic models that couldexplain our data using two methods of inference. Thefirst method involved full-likelihood Bayesian inferenceof genetic and demographic parameters under popula-tion splitting and growth using the BATWING program
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Anglo-Saxon Mass Migration 1011
Tab
le1
Pri
orD
istr
ibut
ions
ofM
ajor
BA
TW
ING
Par
amet
ers
and
Pos
teri
orV
alue
sB
ased
ona
Split
ting
Mod
elB
etw
een
Cen
tral
Eng
land
and
Fri
esla
nd.
PA
RA
ME
TE
RP
RIO
R
PR
IOR
QU
AN
TIL
ES
2.50
%50
%97
.50%
PO
ST
ER
IOR
QU
AN
TIL
ES
2.50
%50
%97
.50%
DY
S19
mut
atio
nra
te..
....
....
....
....
.D
YS
390
mut
atio
nra
te..
....
....
....
....
DY
S39
1m
utat
ion
rate
....
....
....
....
..D
YS
392
mut
atio
nra
te..
....
....
....
....
DY
S39
3m
utat
ion
rate
....
....
....
....
..
Gam
ma(
3,14
59)
Gam
ma(
5,92
9)G
amm
a(3,
878)
Gam
ma(
2,87
8)G
amm
a(1,
878)
0.00
042
0.00
170.
0007
00.
0002
80.
0000
29
0.00
180.
0050
0.00
300.
0019
0.00
079
0.00
500.
011
0.00
820.
0063
0.00
42
0.00
130.
0017
0.00
066
0.00
058
0.00
067
0.00
250.
0033
0.00
140.
0012
0.00
13
0.00
430.
0056
0.00
260.
0022
0.00
25In
itia
lef
fect
ive
popu
lati
onsi
ze..
....
....
.G
row
thra
te..
....
....
....
....
....
....
.T
ime
grow
thst
arts
(in
gene
rati
ons)
....
....
Gam
ma(
1.1,
0.00
01)
Gam
ma(
1.01
,1)
Uni
form
(0,T
MR
CA
a )
371 0.
026
—
7,90
3 0.70
3—
38,9
60 3.71
—
125 0.
029
47
356 0.
0891
987 2.
0219
2
aT
MR
CA
:ti
me
tom
ost
rece
ntco
mm
onan
cest
or.
(URL: http://www.maths.abdn.ac.uk/;ijw), extendedfrom the Markov chain Monte Carlo (MCMC) algorithmpresented by Wilson and Balding (1998). Microsatellitemutation likelihoods were calculated using an unbound-ed symmetric stepwise mutation model. The priors cho-sen for major BATWING parameters are summarized intable 1. Locus-specific priors for the mutation rate pergeneration were based on observed mutations for theseloci, as reported in Heyer et al. (1997), Bianchi et al.(1998), and Kayser et al. (2000), combined with a stan-dard exponential pre-prior. As a precautionary measure,DYS388 was excluded from BATWING analysis (andalso from the Monte Carlo likelihood method describedlater) because no published data on observed meiosesare available for this locus, and therefore, no direct ver-ification exists of stepwise mutation behavior. Unique-event mutations inferred from binary marker data wereused to condition the possible trees but otherwise didnot contribute to the likelihood. Population splitting wasmodeled under strict fission with no subsequent back-ground migration. Population growth was modeled asan exponential from an initially constant effective pop-ulation size. Weakly informative priors were given toother parameters to aid in the convergence of theMCMC process. The prior for initial effective popula-tion size covers the values commonly assumed for theglobal Y chromosome effective population size as wellas lower values to compensate for this being a regionalsample and for representing the effective size beforegrowth. The prior for population growth rate per gen-eration is very flat and gives support to a very widerange of possible values (extending beyond the 2.5%and 97.5% quantiles) to reflect the uncertainty in relatinggrowth in effective population size to growth in real(census) population size. All other parameters, such asthe start-of-growth date and the population split dates,were given flat, uninformative priors.
BATWING suffers from the drawback that infer-ence is based on a model of population differentiationthat involves population splitting only, with no subse-quent migration. In contrast, the MIGRATE method ofBeerli and Felsenstein (2001) and the GENETREEmethod of Bahlo and Griffiths (2000), both also basedon coalescent modeling, allow constant background mi-gration but do not allow population splitting or massmigration at a single point in time. Nielsen and Wakeley(2001) have presented a coalescent-based MCMC infer-ence method that allows both population splitting andmigration, but it is not suitable for microsatellite dataand does not allow for population growth or for addi-tional mass migration events that may occur at specificpoints in time. We therefore developed an alternativeinference method that allowed us to explore more flex-ible models under a range of historical scenarios in-volving both background and mass migration in thepresence of population splitting and growth. This meth-od proceeds through Monte Carlo likelihood estimationbased on summary statistics describing genetic differ-entiation. In what follows, we use the term backgroundmigration to refer to continuous gene flow occurring ineach generation and mass migration to refer to a single
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Table 2Haplogroup Frequencies and Genetic Diversities in Seven British Towns, Friesland and Norway
HAPLOGROUP
NORTH WALES
Llangefni(n 5 80)
Abergele(n 5 18)
MIDLANDS
Ashbourne(n 5 54)
Southwell(n 5 70)
Bourne(n 5 12)
EAST ANGLIA
Fakenham(n 5 53)
N. Walsham(n 5 26)
FRIESLAND
(n 5 94)NORWAY
(n 5 83)
hg1. . . . . . . . . . .hg2. . . . . . . . . . .hg3. . . . . . . . . . .hg9. . . . . . . . . . .hg16. . . . . . . . . .hg21. . . . . . . . . .hg26. . . . . . . . . .Genetic
diversity, h . .
0.8880.0380.0130.013
—0.0380.0130.212
(60.0607)
0.5560.056
———
0.389—
0.569(60.0707)
0.6480.2220.0370.037
—0.056
—0.535
(60.0660)
0.6430.1860.0570.057
—0.057
—0.550
(60.0606)
0.6670.333
—————
0.485(60.1059)
0.5660.415
———
0.019—
0.517(60.0301)
0.5770.3080.0380.038
—0.038
—0.591
(60.0767)
0.5530.3400.0740.011
—0.021
—0.578
(60.0339)
0.2650.4460.2170.0240.0360.012
—0.690
(60.0290)
NOTE.—Dash indicates haplogroup was not observed. Genetic diversities (based on haplogroup frequencies) are given 6 standard error.
large gene flow event. A program was written (availablefrom M.E.W.) to simulate the coalescent under growthfrom an initially constant effective population size, al-lowing a single split TS generations ago of the parentpopulation into two descendent populations, A and B,and subsequent background migration at a rate m, wherea proportion m migrates from population A to B andsimultaneously from B to A in each generation. A fur-ther extension to the program allowed for a single uni-directional migration event from B to A at a time TFgenerations ago, such that lineages in A immediatelyafter this event had a probability F of having just mi-grated from B. Final sample sizes in each populationwere set to match those obtained in our study, and mi-crosatellite repeat sizes in these samples were simulatedusing the unbounded symmetric stepwise mutation mod-el. Parameters for population growth and mutation rateswere set as fixed constants based on BATWING poste-rior modal values and were validated firstly by checkingthat the simulated within-population microsatellite var-iances were similar to observed values and secondlythrough comparison with BATWING results under sce-narios involving no background migration. These pa-rameters were fixed as follows: initial effective popu-lation size 5 300; start of growth 5 80 generations be-fore present (BP); growth rate 5 0.06; ratio of effectivesizes of population A to population B 5 1:1; mutationrates—DYS19 5 0.0023, DYS390 5 0.0030, DYS3915 0.0012, DYS392 5 0.0011, DYS393 5 0.0012. Thesensitivity of inferences to the initial effective popula-tion size was assessed by setting its value an order ofmagnitude higher (to 3000). Inferences considered herewere little affected, and unaffected when (dm)2 was usedas a summary statistic (see below).
Confidence intervals (95%) for the remaining pa-rameters TS, m, TF, and F describing population differ-entiation were estimated by setting constant values forall but one of the parameters and finding the upper andlower limits for the remaining parameter of interest. Pre-set values for the split date TS were chosen to reflectone of the three scenarios: (1) Island model (TS 5 `),(2) Neolithic (TS 5 240 generations BP or 6,000 yearsBP assuming 25 years per generation), and (3) Anglo-Saxon (TS 5 60 generations BP or 1,500 years BP as-suming 25 years per generation). Preset values for the
background migration rate m were set at one of twoextremes: (1) an implausibly low value of m 5 0, and(2) an implausibly high value of m 5 0.1%. The lattervalue is estimated from migration statistics to and fromthe European Economic Area as a whole over the past25 years (source: http://www.homeoffice.gov.uk/rds/index.htm). We regard this as a figure well in excess ofrealistic values for continuous background migrationboth because it is based on figures for the whole ofEurope (i.e., not just Friesland) and because we expectbackground migration in recent times to be very highas a result of modern trends in communication and trav-el. In models that included the parameters F and TF, Fwas always the parameter of interest and TF was setunder an Anglo-Saxon scenario (TF 5 60).
Confidence limits (95%) for the parameter of in-terest were found using RST as a summary statistic ofpopulation differentiation, such that 2.5% of the simu-lated RST values were equal to or more extreme than theobserved RST value when the parameter was set at oneof the two limits, based on 10,000 Monte Carlo itera-tions of the coalescent simulation. Confidence limitswere determined to an accuracy of the least significantdigit stated. We also obtained confidence limits using(dm)2 rather than RST as the summary statistic (Goldsteinet al. 1995) and found these to be similar although gen-erally wider than those obtained using RST.
ResultsPatterns of Genetic Differentiation
The UEP markers defined seven haplogroups (here-after abbreviated to hg) (fig. 2 and table 2), whereas theUEP plus microsatellite markers defined 150 haplotypes(table 3). Hg1 and hg2 predominate in the samples, withhg1 occurring at the highest frequencies in North Walesand hg2 occurring at the highest frequencies in East An-glia, Friesland, and Norway. Hg2 is almost completelyabsent from North Wales. Except for the high frequencyof hg21 in Abergele, the observed haplogroup frequen-cies match their geographic distribution in Europe (Ros-ser et al. 2000). The high frequency of hg21 in Abergelemay indicate high genetic isolation and drift in someparts of North Wales, a hypothesis that is consistent bothwith the tight clustering of Abergele haplotypes within
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Anglo-Saxon Mass Migration 1013
Tab
le3
UE
P1
Mic
rosa
telli
teH
aplo
type
Fre
quen
cies
and
Gen
etic
Div
ersi
ties
inSe
ven
Bri
tish
Tow
ns,
Fri
esla
nd,
and
Nor
way
Ht
#M
icro
sate
llit
eH
aplo
type
aL
lan.
(n5
80)
Abe
r.(n
518
)A
sh.
(n5
54)
Sou
th.
(n5
70)
Bou
r.(n
512
)F
ak.
(n5
53)
N.W
al.
(n5
26)
Fri
es.
(n5
94)
Nor
.(n
583
)To
tal
Cou
nts
Hap
logr
oup
11 2 3 4 5
14-1
2-24
-11-
13-1
314
-12-
23-1
1-13
-13
14-1
2-24
-10-
13-1
314
-12-
25-1
1-13
-13
14-1
2-23
-10-
13-1
3
0.27
50.
063
0.02
50.
113
0.02
5
0.05
6— —
0.11
1—
0.13
00.
111
0.13
00.
037
0.03
7
0.18
60.
086
0.12
90.
014
0.01
4
—0.
083
—0.
083
0.16
7
0.11
30.
094
0.07
50.
038
0.01
9
0.23
10.
077
— —0.
077
0.12
80.
170
0.02
1—
0.02
1
0.06
00.
024
0.03
60.
012
—
72 43 27 18 126 7 8 9 10
14-1
2-24
-11-
13-1
415
-12-
24-1
1-13
-13
15-1
2-24
-10-
13-1
314
-12-
24-1
2-13
-13
15-1
2-23
-11-
13-1
3
0.08
80.
063
—0.
025
—
0.05
60.
056
— —0.
056
—0.
037
0.01
9— —
— — — —0.
029
— — —0.
167
—
— — — —0.
019
— —0.
038
— —
0.01
1—
0.03
2— —
0.01
20.
012
0.01
20.
012
—
10 9 6 5 411 12 13 14 15
14-1
2-25
-11-
13-1
214
-12-
25-1
0-13
-13
14-1
2-24
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314
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1-11
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8— —
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012
—
4 4 4 4 316 17 18 19 20
14-1
3-23
-11-
13-1
314
-12-
25-1
1-14
-13
14-1
2-24
-11-
13-1
214
-12-
23-1
1-13
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14-1
2-24
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13-1
2
0.02
50.
013
0.01
3— —
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0.01
9— — — —
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014
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038
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019
—
— — — — —
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011
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021
— — —0.
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—
3 3 3 3 321 22 23 24 25
14-1
1-23
-11-
13-1
315
-12-
23-1
0-13
-13
14-1
3-24
-11-
13-1
314
-12-
26-1
1-14
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14-1
2-24
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13-1
4
— — —0.
025
—
— — — — —
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019
—0.
014
— — —
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083
— — —
— — — — —
0.07
7— — — —
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021
—0.
011
— — — — —
2 2 2 2 226 27 28 29 30
14-1
2-26
-11-
14-1
314
-12-
25-1
2-13
-13
12-1
2-23
-11-
13-1
314
-12-
22-1
1-13
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16-1
2-25
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13-1
3
—0.
025
— — —
0.05
6— — — —
— — — — —
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014
0.01
4—
— —0.
083
— —
— — —0.
019
—
0.03
8— — — —
— — — — —
— — — —0.
012
2 2 2 2 131 32 33 34 35
11-1
2-24
-11-
13-1
313
-12-
24-1
0-13
-14
14-1
2-24
-11-
14-1
214
-12-
24-1
1-14
-13
14-1
2-24
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14-1
4
0.01
3— —
0.01
3—
— — — —0.
056
— — — — —
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014
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— — — — —
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011
— —
— — — — —
1 1 1 1 136 37 38 39 40
14-1
2-21
-11-
13-1
314
-12-
24-1
2-13
-14
14-1
2-22
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13-1
314
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23-1
1-14
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12-1
2-24
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3
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014
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038
—
0.01
10.
011
— — —
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012
— —
1 1 1 1 141 42 43 44 45 46 47
14-1
2-25
-11-
13-1
413
-12-
23-1
0-13
-13
14-1
2-23
-10-
14-1
314
-12-
26-1
0-13
-13
14-1
2-24
-10-
14-1
314
-12-
24-1
0-13
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2
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1 1 1 1 1 1 1
by guest on April 16, 2013
http://mbe.oxfordjournals.org/
Dow
nloaded from
1014 Weale et al.
Tab
le3
Con
tinu
ed.
Ht
#M
icro
sate
llit
eH
aplo
type
aL
lan.
(n5
80)
Abe
r.(n
518
)A
sh.
(n5
54)
Sou
th.
(n5
70)
Bou
r.(n
512
)F
ak.
(n5
53)
N.W
al.
(n5
26)
Fri
es.
(n5
94)
Nor
.(n
583
)To
tal
Cou
nts
48 49 50 51 52
14-1
3-24
-10-
12-1
312
-12-
24-1
0-13
-13
14-1
4-24
-10-
13-1
214
-14-
25-1
0-13
-13
14-1
2-23
-12-
13-1
3
— — — — —
— — — — —
0.01
9— — — —
—0.
014
— — —
— — — — —
— — — — —
— — — — —
— —0.
011
—0.
011
— — —0.
012
—
1 1 1 1 153 54 55 56 57 58 59
14-1
2-22
-11-
13-1
215
-12-
23-1
2-13
-13
14-1
2-24
-10-
12-1
313
-12-
24-1
0-14
-13
15-1
2-24
-11-
13-1
415
-12-
24-1
1-15
-13
14-1
2-23
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11-1
3
— — — — — — —
— — — — — — —
— — — —0.
019
— —
— — — — —0.
014
—
— — — — — — —
—0.
019
— — — — —
— — — — — — —
— —0.
011
0.01
1— —
0.01
1
0.01
2— — — — — —
1 1 1 1 1 1 1
Hap
logr
oup
260 61 62 63 64 65
14-1
4-22
-10-
11-1
314
-14-
23-1
0-11
-13
15-1
4-23
-10-
11-1
315
-14-
22-1
0-11
-13
15-1
3-23
-10-
12-1
415
-13-
23-1
0-12
-15
— — — — — —
— — — — — —
0.09
30.
019
— — — —
0.02
90.
014
— —0.
014
0.02
9
0.08
30.
083
—0.
083
— —
0.09
40.
113
0.01
9— —
0.01
9
0.07
7— — —
0.07
7—
0.05
30.
032
0.02
10.
011
0.01
10.
021
0.08
40.
133
0.07
20.
048
0.02
4—
27 23 9 6 6 566 67 68 69 70
15-1
5-23
-10-
11-1
316
-14-
22-1
0-11
-13
14-1
4-22
-10-
11-1
417
-13-
25-1
1-11
-13
16-1
3-24
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11-1
3
— — —0.
025
—
— — — — —
—0.
019
— — —
—0.
014
— — —
— — — — —
0.01
9—
0.01
9—
0.03
8
0.07
7— — — —
0.01
1—
0.01
1— —
—0.
012
0.01
2— —
4 3 3 2 271 72 73 74 75
16-1
3-23
-10-
12-1
514
-14-
23-1
1-11
-13
16-1
3-23
-10-
12-1
314
-14-
22-1
1-11
-12
15-1
4-22
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11-1
3
— — — — —
— — — — —
— — —0.
019
0.01
9
— —0.
014
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019
0.01
9
— — — — —
0.02
10.
011
0.01
1— —
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012
— — —
2 2 2 2 276 77 78 79 80
15-1
3-24
-10-
12-1
514
-14-
22-1
1-11
-13
15-1
2-22
-10-
10-1
315
-12-
22-1
1-11
-14
15-1
3-22
-10-
11-1
3
0.01
3— — — —
— — — — —
— — — — —
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014
—
0.08
3— — — —
— —0.
019
— —
— — — — —
— — — —0.
011
—0.
012
— — —
2 1 1 1 181 82 83 84 85
15-1
3-22
-10-
11-1
415
-13-
23-0
9-12
-14
15-1
3-23
-10-
12-1
314
-14-
22-0
9-11
-13
13-1
4-22
-10-
11-1
3
— — — — —
— — — —0.
056
— — — — —
— — — — —
— — — — —
— — — — —
0.03
80.
038
— — —
— —0.
011
0.01
1—
— — — — —
1 1 1 1 186 87 88 89 90
15-1
3-23
-11-
11-1
315
-13-
23-1
1-12
-14
15-1
2-21
-10-
11-1
415
-14-
22-0
9-11
-13
14-1
3-22
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11-1
5
— — — — —
— — — — —
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019
— — —
— —0.
014
— —
— — — — —
— — —0.
019
—
— — — — —
0.01
1— — —
0.01
1
— — — — —
1 1 1 1 191 92
14-1
6-22
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11-1
414
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22-1
0-11
-13
— —— —
—0.
019
— —— —
— —— —
0.01
1—
— —1 1
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http://mbe.oxfordjournals.org/
Dow
nloaded from
Anglo-Saxon Mass Migration 1015
Tab
le3
Con
tinu
ed.
Ht
#M
icro
sate
llit
eH
aplo
type
aL
lan.
(n5
80)
Abe
r.(n
518
)A
sh.
(n5
54)
Sou
th.
(n5
70)
Bou
r.(n
512
)F
ak.
(n5
53)
N.W
al.
(n5
26)
Fri
es.
(n5
94)
Nor
.(n
583
)To
tal
Cou
nts
93 94 95 96
15-1
4-24
-10-
11-1
315
-14-
24-1
0-12
-15
15-1
5-22
-10-
11-1
315
-15-
22-1
0-12
-13
— — — —
— — — —
— — — —
— — — —
— — — —
0.01
9— — —
— — — —
—0.
011
—0.
011
— —0.
012
—
1 1 1 197 98 99 100
101
14-1
6-22
-09-
11-1
414
-15-
22-1
0-11
-14
14-1
5-22
-10-
11-1
316
-13-
23-1
0-13
-13
14-1
2-21
-10-
11-1
4
— — — — —
— — — — —
— — — —0.
019
0.01
4— —
0.01
4—
— — — — —
— — — — —
— — — — —
—0.
011
0.01
1— —
— — — — —
1 1 1 1 110
210
310
410
510
6
16-1
3-24
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12-1
414
-14-
22-1
0-12
-13
17-1
3-22
-10-
11-1
417
-13-
23-1
1-11
-14
17-1
3-24
-10-
12-1
5
— — — — —
— — — — —
— — — — —
0.01
4— — — —
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— — — — —
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011
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011
—
— —0.
012
—0.
012
1 1 1 1 1
Hap
logr
oup
310
710
810
911
011
1
16-1
2-25
-11-
11-1
315
-12-
25-1
0-11
-13
15-1
2-25
-11-
11-1
316
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25-1
0-11
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16-1
2-24
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11-1
3
— — — — —
— — — — —
0.01
9— —
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0.01
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4
— — — — —
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0.03
60.
048
0.02
40.
012
0.01
2
5 4 3 2 211
211
311
411
511
6
15-1
2-26
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11-1
317
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25-1
0-11
-13
15-1
2-25
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11-1
415
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26-1
0-11
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4-25
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11-1
3
— — — — —
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014
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— — — — —
— — — — —
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011
—
0.02
4—
0.01
2—
0.01
2
2 1 1 1 111
711
811
912
012
1
16-0
9-25
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11-1
316
-10-
25-1
0-11
-13
16-1
0-26
-10-
11-1
315
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25-1
0-11
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15-1
2-24
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11-1
3
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013
— —
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0.01
10.
011
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—
— — — —0.
012
1 1 1 1 112
212
312
412
512
612
7
16-1
2-25
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11-1
414
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25-1
0-11
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16-1
2-26
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11-1
317
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24-1
0-11
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17-1
2-23
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11-1
317
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23-1
1-11
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— — — — — —
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4— — — — —
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—
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1 1 1 1 1 1
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logr
oup
912
812
913
013
1
14-1
6-23
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11-1
216
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24-1
0-11
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5-26
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11-1
214
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23-1
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013
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4
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038
—
— — — —
0.01
2— — —
3 1 1 113
213
313
413
513
6
14-1
6-24
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11-1
215
-15-
23-1
0-11
-12
15-1
5-24
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11-1
215
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9-11
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11-1
3
— — — — —
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019
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011
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—
1 1 1 1 1
by guest on April 16, 2013
http://mbe.oxfordjournals.org/
Dow
nloaded from
1016 Weale et al.
Tab
le3
Con
tinu
ed.
Ht
#M
icro
sate
llit
eH
aplo
type
aL
lan.
(n5
80)
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r.(n
518
)A
sh.
(n5
54)
Sou
th.
(n5
70)
Bou
r.(n
512
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ak.
(n5
53)
N.W
al.
(n5
26)
Fri
es.
(n5
94)
Nor
.(n
583
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tal
Cou
nts
Hap
logr
oup
1613
713
813
9
15-1
2-23
-11-
14-1
414
-12-
23-1
1-14
-14
14-1
2-24
-11-
14-1
4
— — —
— — —
— — —
— — —
— — —
— — —
— — —
— — —
0.01
20.
012
0.01
2
1 1 1
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logr
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2114
014
114
2
13-1
2-24
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11-1
313
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13-1
2-25
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3
0.02
5— —
0.22
20.
056
—
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—
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029
0.01
4
— — —
— —0.
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— — —
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—
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2— —
7 6 2
143
144
145
146
147
148
149
14-1
2-24
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11-1
313
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23-1
0-11
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13-1
2-24
-10-
11-1
413
-12-
22-1
0-11
-13
13-1
2-24
-12-
11-1
313
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23-1
0-12
-13
14-1
2-23
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11-1
3
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— —0.
056
— — —0.
056
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019
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— — — — — — —
— — — — — — —
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038
—
— — — — — — —
— — — — — — —
1 1 1 1 1 1 1
Hap
logr
oup
2615
013
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23-1
0-12
-13
0.01
3—
——
——
——
—1
Gen
etic
dive
rsit
y,h
0.89
96
0.02
390.
954
60.
0394
0.94
96
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945
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0.97
06
0.04
430.
954
60.
0123
0.93
56
0.03
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952
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0134
0.96
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0.00
96
NO
TE.—
Mic
rosa
tell
ite
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otyp
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ithi
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plog
roup
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ear
rang
edin
decr
easi
ngor
der
ofto
tal
freq
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y.D
ash
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cate
sha
plot
ype
was
not
obse
rved
.G
ene
tic
dive
rsit
ies
(bas
edon
hapl
otyp
efr
eque
ncie
s)ar
egi
ven6
stan
dard
erro
r. aM
icro
sate
llit
eha
plot
ypes
are
defi
ned
bya
stri
ngof
six
num
bers
givi
ngth
ere
peat
size
atlo
ciD
YS
19,
DY
S38
8,D
YS
390,
DY
S39
1,D
YS
392,
and
DY
S39
3,re
spec
tive
ly.
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nloaded from
Anglo-Saxon Mass Migration 1017
Table 4Genetic Distances and P-values
Llangefni Abergele Ashbourne Southwell Bourne Fakenham N. Walsham Friesland Norway
Llangefni . . . .Abergele . . . . .Ashbourne . . .Southwell . . . .Bourne . . . . . .Fakenham. . . .N. Walsham . .Friesland. . . . .Norway. . . . . .
0.1230.1680.1260.2020.2340.1740.1840.310
0.008*
0.0810.0630.0820.1120.0820.0970.175
,0.001*0.002*
20.01320.03420.00420.02420.001
0.081
,0.001*,0.001*
0.707
20.0310.006
20.0240.0040.093
,0.001*0.048*0.0930.082
20.03020.05220.031
0.067
,0.001*,0.001*
0.1880.2330.117
20.01720.007
0.038
,0.001*,0.001*
0.0800.1410.0610.032*
20.0170.065
,0.001*,0.001*
0.1810.1150.1720.1530.551
0.044
,0.001*0.002*
,0.001*,0.001*
0.2370.037*0.008*
,0.001*
NOTE.—Upper right triangle reports P-values of pairwise exact tests for population differentiation (Raymond and Rousset 1995) based on UEP 1 microsatellitehaplotype frequencies. Asterisk indicates a significant value (P , 0.05). Lower left triangle reports AMOVA-based RST values (Michalakis and Excoffier 1996)based on microsatellite haplotypes defined from six loci: DYS19, DYS388, DYS390, DYS391, DYS392, and DYS393.
FIG. 3.—Principal coordinates plot of RST values reported in table4. The first and second projections (PCO1 and PCO2) explain 59%and 20% of the variation, respectively.
this haplogroup and with the lower genetic diversityfound in Llangefni.
Several patterns emerge from analyses of geneticdistance and population differentiation (table 4 and fig.3). Firstly, little genetic differentiation exists among theCentral English towns. The only significant differencein haplotype frequencies occurs between the neighbor-ing towns of Fakenham and North Walsham (P 5 0.032for individual pairwise comparison or P 5 0.035 forcombined test of all English towns). Although more hg1and fewer hg2 chromosomes were observed in the Mid-lands than in East Anglia (table 2), Mantel tests on thegenetic versus geographic distance correlation and linearregression on hg1 and hg2 frequencies reveal no signif-icant within-England clinal patterns.
Secondly, in contrast to the Central English towns,the two North Welsh towns show highly significant dif-ferences, both from each other and from the five CentralEnglish towns. Llangefni has a very high frequency ofhg1, tightly clustered around the modal haplotype (hap-lotype #1 in table 3; haplotype 1.15 in Wilson et al.2001) that has been found at high frequency in otherAtlantic populations, including Ireland (Hill, Jobling,and Bradley 2000) and the Orkneys (Wilson et al. 2001).
Both Llangefni and Abergele have very low frequenciesof hg2 and dispersed haplotypes within this haplogroup,a pattern which is consistent with these haplotypes en-tering the North Welsh populations through separate, in-frequent admixture events.
Thirdly, no significant differences in haplotype fre-quencies exist between Friesland and any of the CentralEnglish towns. Comparisons between Norway and theCentral English towns, on the other hand, are all signif-icant, apart from Bourne (P 5 0.237), which may beexplained by the small number of samples collectedfrom this town (n 5 12). Furthermore, bootstrap testson RST values revealed that the Central English (all fivetowns combined) are significantly more closely relatedto the Frisians than they are to the North Welsh (Llan-gefni: P , 0.001; Abergele: P 5 0.046) or to the Nor-wegians (P 5 0.005). Both Friesland and Norway aresignificantly different from the North Welsh towns. Sim-ilar results were obtained using FST values based on hap-logroup frequencies, but tests on FST values based onhaplotype frequencies were not significant because ofthe large number of singletons at this level. Taken to-gether, these results suggest considerable male-line com-monality between Central England and Friesland.
Wilson et al. (2001) identified two haplotypes—(1)2.47 (haplotype #60 in our table 3), and (2) 3.65 (hap-lotype #107 in our table 3)—that proved useful in in-ferring a Viking contribution to the Orcadian gene pool,although they noted that it might not be possible to dis-tinguish 2.47 from an Anglo-Saxon contribution in otherparts of Britain. We compared the frequencies found inthe Central English, Frisian, and Norwegian samples of(1) the 2.47 and 3.65 haplotypes on their own, (2) thesetwo haplotypes plus their one-step mutational neighbors,and (3) these two haplotypes plus their one-step net-works (defined as all haplotypes within a sample con-nected to the named haplotype by a series of one-stepmutations via observed intermediate haplotypes). Assuggested by the results in the previous paragraph, ineach case the frequency distribution in Central Englandmore closely matched that in Friesland than that in Nor-way. Thus, neither of these two haplotypes provided anypositive evidence of a (Norwegian) Viking contributionto the Central English gene pool that could not be ex-
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plained by a substantial contribution originating inFriesland only.
Population Genetic Models
We explored various population genetic models(see Materials and Methods) to evaluate whether or nota large Anglo-Saxon migration event is needed to ex-plain the extremely high Central English-Frisian affinity.We started with a simple model of population fissionwith no background migration. We found a 95% credibleinterval for the split date using BATWING of 0–88 gen-erations (0–2,200 years BP, assuming 25 years per gen-eration), which corresponded well with the 95% confi-dence interval from the Monte Carlo likelihood methodwith no background migration (0–91 generations or 0–2,275 years BP assuming 25 years per generation).
Next, we looked at the levels of background mi-gration, operating continuously from generation to gen-eration, needed to maintain the Central English-Frisiangenetic similarity under two other scenarios not involv-ing Anglo-Saxon mass migration. Under an Island Mod-el scenario (constant background migration between twopopulations that split at TS 5 `) the 95% confidenceinterval for m, estimated from the Monte Carlo likeli-hood method, is 0.3%–50% (where 50% indicates com-plete panmixia and is a maximum value for m). Thesame result (to the significant digit given) is found undera Neolithic mass migration scenario (population split240 generations BP). We note that a figure of m 5 0.3%is three times higher than the figure we estimated asrepresenting an implausibly high value for m, well inexcess of realistic values, based on migration statisticsto and from the European Economic Area as a wholeover the past 25 years. If we set m at the implausiblyhigh value of 0.1%, the 95% confidence interval for aCentral English-Frisian split date is 0–97 generations(0–2,425 years BP, assuming 25 years per generation).The figure of 97 generations BP represents an extremeupper limit for the migration event in this case bothbecause it is based on such an implausibly high valuefor background migration and because it requires themost severe mass migration event imaginable, namely a100% replacement of the English Y chromosome pool.
Next, we assumed that an Anglo-Saxon migrationevent did take place 60 generations ago (i.e., 1,500 yearsBP assuming 25 years per generation) and asked howbig an event would be needed to explain the CentralEnglish-Frisian genetic similarity. If the Central Englishand Frisian populations were very different at the timeof the event, a larger mass migration would be needed.We therefore started by assuming complete genetic iden-tity of the two populations at the time of the Neolithic(i.e., a Central English-Frisian population split 240 gen-erations BP). Assuming no background migration, the95% confidence interval of the proportion F of the Cen-tral English population derived from an Anglo-Saxonmass migration event is 65%–100%. If a backgroundmigration rate since the Neolithic of m 5 0.1% is al-lowed, the 95% confidence interval for F widens to50%–100%. This result is unchanged if a 30-year gen-
eration time is assumed (i.e., an Anglo-Saxon migrationevent 50 rather than 60 generations ago).
Discussion
Our results indicate the presence of a strong geneticbarrier between Central England and North Wales andthe virtual absence of a barrier between Central Englandand Friesland. Any attempt to explain these results interms of demographic history and migration needs toencompass both these findings satisfactorily. The Cen-tral English-North Welsh barrier cannot be explainedpurely as a simple isolation-by-distance phenomenonbecause it contrasts strongly with the lack of evidencefor a cline among the five widely separated Englishtowns. Our findings are particularly striking, given thehigh resolution and rapid mutation rate of the Y chro-mosome haplotypes on which they are based. These al-low genetic barriers, if they exist, to be clearly defined.
The best explanation for our findings is that theAnglo-Saxon cultural transition in Central England co-incided with a mass immigration from the continent.Such an event would simultaneously explain both thehigh Central English-Frisian affinity and the low CentralEnglish-North Welsh affinity. If we use a rate of 0.1%,as observed over the past 25 years, to represent an ex-tremely high value for continuous background migrationbetween Central England and continental Europe, thenwe estimate that an Anglo-Saxon immigration event af-fecting 50%–100% of the Central English male genepool at that time is required. We note, however, that ourdata do not allow us to distinguish an event that simplyadded to the indigenous Central English male gene poolfrom one where indigenous males were displaced else-where or one where indigenous males were reduced innumber. Furthermore, although our models assume asingle instantaneous migration event, we would also ex-pect a more gradual process lasting several generationsbut still resulting in the same degree of admixture (apicture which may fit the historical data better [Harke2002]) to produce very similar genetic patterns.
We accept that our data do not prove conclusivelythat an Anglo-Saxon mass migration event took place.If a background migration rate of 0.3% is allowed be-tween Central England and Friesland, then the need fora mass migration event disappears. However, we notethat this is an extremely high rate even by modern stan-dards and would have to have been maintained contin-uously over thousands of years. A background migrationrate of 0.3% would imply that one in six of today’sCentral English males descend from Frisians (or a pop-ulation identical to Frisians) that emigrated to Englandafter the Anglo-Saxon period and that an equal propor-tion of today’s Frisians descend from English in a likemanner. We also note that under a unidirectional geneflow model involving immigration into Central Englandonly, the rate of background migration would then haveto double to be at least 0.6% on a continuous basis.
It is also true that a mass migration event couldhave occurred outside the Anglo-Saxon migration periodbecause the 95% confidence interval for a Central En-
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glish-Frisian split extends as far back as 425 B.C. (if oneallows a background migration rate of 0.1% and a gen-eration time of 25 years). Archaeology and the testi-mony of Caesar combine to suggest an immigration ofthe Belgae, a Celtic tribe from northern Gaul, into cen-tral southern England (Hampshire and West Sussex) be-tween 100 and 80 B.C. (Hawkes 1968; Cunliffe 1988,pp. 147–149; Cunliffe 1991, pp. 108–110). Furthermore,although Friesland lay outside the maximum extent ofthe Roman Empire, small numbers of Frisian mercenar-ies were recruited by the Romans and stationed as farnorth as Hadrian’s Wall (Breeze and Dobson 1978, pp.139–140; Collingwood, Wright, and Tomlin 1995, p.501). However, most historians would see these move-ments, if they would acknowledge them at all, as pre-ludes to post-Roman Anglo-Saxon migration, and itwould be odd indeed to deny the latter while at the sametime assigning an extremely large mass migration statusto the former.
Finally, we accept that our inferences are based onpopulation genetic analyses that assume a particularmodel of microsatellite evolution under selective neu-trality and growth and that departures from these as-sumptions may influence our results. However, we notethat the accuracy of the mutation model is diminishedin importance by the small number of generations thatwould allow new mutations to accumulate since Anglo-Saxon times and also that any selective sweeps wouldalso have to have been very recent in order to haveinfluenced our conclusions greatly, especially becausethe effects of such sweeps would partly be accommo-dated by our model of exponential population growth.In addition, the estimates provided by BATWING foreffective population sizes at the time of the Anglo-Sax-on migration event are very small (table 1). Thus, alarge amount of error caused by drift is already allowedfor by our BATWING and Monte Carlo likelihood anal-yses. We do not presume an exact correspondence be-tween real and effective population size dynamics orbetween the real population history of England, whichhas seen many different changes in size, and our simplemodel of exponential growth. However, we note that theposterior mode of the effective population growth rateper generation provided by BATWING (6.0%) almostexactly matches the real estimated population growthrate averaged over the past 1,500 years (Hatcher 1977,pp. 1348–1530; Wrigley and Schofield 1989, pp. 1541–1871; Harke 2002), whereas our 95% credible intervalcovers both the lower average growth rates of A.D. 500–1750 (approximately 3% per 25 years, albeit with largefluctuations) and the higher average growth rates of A.D.1750–2000 (approximately 23% per 25 years).
Anglo-Saxon settlements and culture appearedthroughout England but, importantly, did not extend intoNorth Wales, where many of the original Celtic Britonsliving in England are thought to have fled (Kearney1989; Davies 1993, 1999). Conflict between the Welshand Anglo-Saxon kingdoms continued over a long pe-riod. Offa’s Dyke (an earthwork barrier 240 km long)was constructed ca. A.D. 790 and provided a well-de-fined boundary between England and Wales. The lin-
guistic, cultural, and political separation of the two re-gions lasted at least until A.D. 1282 when Edward I ofEngland defeated the Welsh King Llywelyn II (Davies1993). Our results suggest that this separation has alsorestricted male-mediated gene flow between the two re-gions over the past approximately 1500 years.
Comparisons of Central English and Norwegianhaplotypes reveal no evidence of distinctive commonsignature haplotypes indicative of Viking origin, in con-trast to Orcadian-Norwegian comparisons (Wilson et al.2001). However, the Vikings who may have settled inEast Anglia and the Midlands are thought to have beenpredominantly from Denmark, rather than Norway(Richards 2000). Previously published data suggest thatthe Danish have greater Y chromosome genetic affinitywith the English than with the Norwegians (Malaspinaet al. 2000; Rosser et al. 2000). However, the Danish-German border is believed to be another source locationof the Anglo-Saxons (Kearney 1989; Davies 1999), soany Danish Viking influence on the English gene poolmay prove difficult to distinguish from Anglo-Saxon in-fluence. Further studies within Scandinavia and else-where are needed to resolve this issue.
This study shows that the Welsh border was moreof a genetic barrier to Anglo-Saxon Y chromosome geneflow than the North Sea. Remarkably, we find that theresultant genetic differentiation is still discernible in thepresent day. These results indicate that a political bound-ary can be more important than a geophysical one inpopulation genetic structuring and that informative pat-terns of genetic differentiation can be produced by mi-gration events occurring within historical times.
Acknowledgments
We thank all of the Y chromosome donors whocontributed to this study and M. A. Strøksnes, Drs. P.Clark, M. Gee, P. R. Gage, S. J. Keen, M. R. Green-wood, J. D. Peterson, Kirtley, A. Hawkes, L. J. Moore,and M. Sears for helping to collect the samples. Wethank Heinrich Harke, Lounes Chikhi, and two anony-mous referees for valuable comments on an earlier draftof this paper. M.G.T. is supported by a Nuffield Foun-dation grant (NUF-NAL).
LITERATURE CITED
ADAMS, W. Y. 1968. Invasion, diffusion, evolution? Antiquity42:194–215.
ADAMS, W. Y., D. P. VAN GERVEN, and R. S. LEVY. 1978. Theretreat from migrationism. Annu. Rev. Anthropol. 7:483–532.
ANTHONY, D. W. 1990. Migration in archaeology: the baby andthe bathwater. Am. Anthropol. 92:895–914.
ARNOLD, C. J. 1984. From Roman Britain to Saxon England.Croom Helm, London.
BAHLO, M., and R. C. GRIFFITHS. 2000. Inference from genetrees in a subdivided population. Theor. Popul. Biol. 57:79–95.
BEERLI, P., and J. FELSENSTEIN. 2001. Maximum likelihoodestimation of a migration matrix and effective populationsizes in n subpopulations by using a coalescent approach.Proc. Natl. Acad. Sci. USA 98:4563–4568.
by guest on April 16, 2013
http://mbe.oxfordjournals.org/
Dow
nloaded from
1020 Weale et al.
BIANCHI, N. O., C. I. CATANESI, G. BAILLIET, V. L. MARTINEZ-MARIGNAC, C. M. BRAVI, L. B. VIDAL-RIOJA, R. HERRERA,and J. S. LOPEZ-CAMELO. 1998. Characterization of ances-tral and derived Y-chromosomal haplotypes of New Worldpopulations. Am. J. Hum. Genet. 63:1862–1871.
BODMER, W. F. 1993. The genetics of Celtic populations. Proc.Br. Acad. 82:37–57.
BREEZE, D. J., and B. DOBSON. 1978. Hadrian’s Wall, Revisededition. Pelican, Harmondsworth.
BURMEISTER, S. 2000. Archaeology and migration: approachesto an archaeological proof of migration. Curr. Anthropol.41:539–567.
CARTWRIGHT, R. A., H. J. HARGREAVES, and E. SUNDERLAND.1977. Serum protein and isoenzyme polymorphisms fromNottingham, England. Hum. Biol. 49:629–640.
CASALOTTI, R., L. SIMONI, M. BELLEDI, and G. BARBUJANI.1999. Y-chromosome polymorphisms and the origins of theEuropean gene pool. Proc. R. Soc. Lond. B 266:1959–1965.
CAVALLI-SFORZA, L. L., P. MENOZZI, and A. PIAZZA. 1994. Thehistory and geography of human genes. Princeton Univer-sity Press, Princeton, NJ.
CHAPMAN, J. 1997. The impact of modern invasions and mi-grations on archaeological explanation. Pp. 11–20 in J.CHAPMAN and H. HAMEROW, eds. Migrations and invasionsin archaeological explanation. BAR International Series664, Oxford, UK.
CHAPMAN, J., and H. HAMEROW, eds. 1997. Migrations andinvasions in archaeological explanation. BAR InternationalSeries 664, Oxford, UK.
CLARK, G. 1966. The invasion hypothesis in British archaeol-ogy. Antiquity 40:172–189.
COLLINGWOOD, R. G., R. P. WRIGHT, and R. S. O. TOMLIN.1995. The Roman inscriptions of Britain, Vol. 1, 2nd edi-tion. Sutton, Stroud.
CRAWFORD, S. 1997. Britons, Anglo-Saxons and the Germanicburial ritual. Pp. 45–72 in J. CHAPMAN and H. HAMEROW,eds. Migrations and invasions in archaeological explana-tion. BAR International Series 664, Oxford, UK.
CUNLIFFE, B. 1988. Greeks, Romans and Barbarians: spheresof interaction. Batsford, London.
———. 1991. Iron Age communities in Britain. 3rd edition(Archaeology of Britain series). Routledge, London.
DAVIES, J. 1993. A History of Wales. Penguin Press, London.DAVIES, N. 1999. The Isles: a history. Macmillan, London.ESMONDE-CLEARY, A. S. 1993. Approaches to the differences
between Late Romano-British and Early Anglo-Saxon ar-chaeology. Anglo-Saxon Stud. Archaeol. Hist. 6:57–63.
FALSETTI, A. B., and R. R. SOKOL. 1993. Genetic structure ofhuman populations in the British Isles. Ann. Hum. Biol. 20:215–229.
GOLDSTEIN, D. B., A. RUIZ LINARES, L. L. CAVALLI-SFORZA,and M. W. FELDMAN. 1995. Genetic absolute dating basedon microsatellites and the origin of modern humans. Proc.Natl. Acad. Sci. USA 92:6723–6727.
HAMEROW, H. 1997. Migration theory and the Anglo-Saxon‘‘identity crisis.’’ Pp. 33–44 in J. CHAPMAN and H. HAM-EROW, eds. Migrations and invasions in archaeological ex-planation. BAR International Series 664, Oxford, UK.
HARKE, H. 1998. Anthropologists and migrations: a problemof attitude? Curr. Anthropol. 39:19–45.
———. 2002. Kings and warriors: population and landscapein early medieval Britain. Pp. 145–175 in P. SLACK and R.WARD, eds. The peopling of Britain: the shaping of a hu-man landscape. Oxford University Press, Oxford.
HATCHER, J. 1977. Plague, population and the English econo-my. Palgrave Macmillan, London.
HAWKES, C. F. C. 1968. New thoughts on the Belgae. Antiquity42:6–16.
HAWKES, J., and C. HAWKES. 1942. Prehistoric Britain. Pen-guin, Harmondsworth, United Kingdom.
HELGASON, A., S. SIGURDARDOTTIR, J. NICHOLSON, B. SYKES,E. W. HILL, D. G. BRADLEY, V. BOSNES, J. R. GULCHER, R.WARD, and K. STEFANSSON. 2000. Estimating Scandinavianand Gaelic ancestry in the male settlers of Iceland. Am. J.Hum. Genet. 67:697–717.
HEYER, E., J. PUYMIRAT, P. DIELTJES, E. BAKKER, and P. DE
KNIJFF. 1997. Estimating Y chromosome specific microsat-ellite mutation frequencies using deep rooting pedigrees.Hum. Mol. Genet. 6:799–803.
HIGHAM, N. 1992. Rome, Britain and the Anglo–Saxons. Sea-by, London.
HILL, E. W., M. A. JOBLING, and D. G. BRADLEY. 2000. Y-chromosome variation and Irish origins. Nature 404:351–352.
HODGES, R. 1989. The Anglo–Saxon achievement: archaeologyand the beginnings of English society. Duckworth, London.
HUNTER, J., and I. RALSON, eds. 1998. The archaeology ofBritain. Routledge, London.
KAYSER, M., S. BRAUER, G. WEISS, W. SCHIEFENHOVEL, P. A.UNDERHILL, and M. STONEKING. 2001. Independent histo-ries of human Y chromosomes from Melanesia and Austra-lia. Am. J. Hum. Genet. 68:173–190.
KAYSER, M., A. CAGLIA, D. CORACH et al. (30 co-authors).1997. Evaluation of Y-chromosomal STRs: a multicenterstudy. Int. J. Legal Med. 110:125–133.
KAYSER, M., L. ROEWER, M. HEDMAN et al. (14 co-authors).2000. Characteristics and frequency of germline mutationsat microsatellite loci from the human Y chromosome, asrevealed by direct observation in father/son pairs. Am. J.Hum. Genet. 66:1580–1588.
KEARNEY, H. 1989. The British Isles: a history of four nations.Cambridge University Press, Cambridge.
LEEDS, E. T. 1954. The growth of Wessex. Oxoniensia 19:45–60.
LONG, C. C., C. DARKE, and R. MARKS. 1998. Celtic ancestry,HLA phenotype and increased risk of skin cancer. Br. J.Dermatol. 138:627–630.
MALASPINA, P., F. CRUCIANI, P. SANTOLAMAZZA et al. (24 co-authors). 2000. Patterns of male-specific inter-population di-vergence in Europe, West Asia and North Africa. Ann.Hum. Genet. 64:395–412.
MASCIE-TAYLOR, C. G. N., and G. W. LASKER. 1996. Furthernotes on possible changes in the geographic distribution ofABO and Rh blood groups in Great Britain. Hum. Biol. 68:473–478.
MASTANA, S. S., R. JAYASEKARA, P. FISHER, R. J. SOKOL, andS. S. PAPIHA. 1993. Genetic polymorphism of orosomucoid(ORM) in populations of the United Kingdom, Indian sub-continent, and Cambodia. Jpn. J. Hum. Genet. 38:289–296.
MASTANA, S. S., and R. J. SOKOL. 1998. Genetic variation inthe East Midlands. Ann. Hum. Biol. 25:43–68.
MERRYWEATHER-CLARKE, A. T., J. J. POINTON, J. D. SHEAR-MAN, and K. J. H. ROBSON. 1997. Global prevalence ofputative haemochromatosis mutations. J. Med. Genet. 34:275–278.
MICHALAKIS, Y., and L. EXCOFFIER. 1996. A generic estimationof population subdivision using distances between alleleswith special reference for microsatellite loci. Genetics 142:1061–1064.
MYRES, J. N. L. 1986. The English settlements. Oxford Uni-versity Press, Oxford.
NASMAN, U. 1988. Den folkvandringstiden krisen i Sydskan-dinavien, inklusive Oland och Gotland. Pp. 227–255 in U.
by guest on April 16, 2013
http://mbe.oxfordjournals.org/
Dow
nloaded from
Anglo-Saxon Mass Migration 1021
NASMAN and J. LUND, eds. Folkevandringstiden i Norden:En krisetid mellem œldre og yngre jernalder. Aarhus Univ-ersitetsforlag, Aarhus.
NEI, M. 1987. Molecular evolutionary genetics. Columbia Uni-versity Press, New York.
NIELSEN, H. F. 1985. Old English and the continental Germaniclanguages: a survey of morphological and phonological in-terrelations. 2nd edition. Institut fur Sprachwissenschaft derUniversitat Innsbruck, Innsbruck.
NIELSEN, R., and J. WAKELEY. 2001. Distinguishing migrationfrom isolation: a Markov chain Monte Carlo approach. Ge-netics 158:885–896.
PAPIHA, S. S., M. F. DUGGAN KEEN, and R. S. E. RODGER.1985. DR antigens and Bf allotypes in northeast England,UK. Hum. Hered. 35:246–250.
PETERSEN, P. V. 1991. Nye fund af metalsager fra yngre ger-mansk jernalder: Detektorfund og danefæ fra perioden1966–88. Pp. 49–65 in P. MORTENSEN and B. M. RASMUS-SEN, eds. Fra Stamme til Stat i Danmark 2:Høvdingesamfund og Kongemagt. Aarhus Universitetsfor-lag, Aarhus.
POOLEY, C., and J. TURNBULL. 1998. Migration and mobilityin Britain since the eighteenth century. UCL Press, London.
POSER, C. M. 1994. The dissemination of multiple-sclerosis—a viking saga—a historical essay. Ann. Neurol. 36:S231–S243.
RAYMOND, M., and F. ROUSSET 1995. An exact test for popu-lation differentiation. Evolution 49:1280–1283.
RENFREW, C. 1987. Archaeology and language: the puzzle ofIndo–European origins. Jonathan Cape, London.
REYNOLDS, J., B. S. WEIR, and C. C. COCKERHAM. 1983. Es-timation of the coancestry coefficient: basis for a short-termgenetic distance. Genetics 105:767–779.
RICHARDS, J. D. 2000. Viking age England. Stroud, Tempus.RICHARDS, M., V. MACAULAY, E. HICKEY et al. (37 co-au-
thors). 2000. Tracing European founder lineages in the NearEastern mtDNA pool. Am. J. Hum. Genet. 67:1251–1276.
ROSSER, Z. H., T. ZERJAL, M. E. HURLES et al. (63 co-authors).2000. Y-chromosomal diversity in Europe is clinal and in-fluenced primarily by geography, rather than by language.Am. J. Hum. Genet. 67:1526–1543.
SEMINO, O., G. PASSARINO, P. J. OEFNER et al. (17 co-authors).2000. The genetic legacy of Paleolithic Homo sapiens sa-piens in extant Europeans: a Y chromosome perspective.Science 290:1155–1159.
SIMONI, L., F. CALAFELL, D. PETTENER, J. BERTRANPETIT, andG. BARBUJANI. 2000. Geographic patterns of mtDNA di-versity in Europe. Am. J. Hum. Genet. 66:262–278.
SHENNAN, S. 2000. Population, culture, history, and the dy-namics of culture change. Curr. Anthropol. 41:811–835.
THOMAS, M. G., N. BRADMAN, and H. M. FLINN. 1999. Highthroughput analysis of 10 microsatellite and 11 binary poly-morphisms on the human Y-chromosome. Hum. Genet.105:577–581.
THOMAS, M. G., K. SKORECKI, H. BEN-AMI, T. PARFITT, N.BRADMAN, and D. B. GOLDSTEIN. 1998. Origins of Old Tes-tament priests. Nature 394:138–140.
TORRONI, A., H. BANDELT, H. D’URBANO et al. (11 co-au-thors). 1998. mtDNA analysis reveals a major Late Paleo-lithic population expansion from southwestern to north-eastern Europe. Am. J. Hum. Genet. 62:1137–1152.
TYFIELD, L. A., M. J. OSBORN, and J. B. HOLTON. 1997. Se-quence variation at the phenylalanine hydroxylase gene inthe British Isles. Am. J. Hum. Genet. 60:388–396.
UNDERHILL, P. A., P. SHEN, A. A. LIN et al. (21 co-authors).2000. Y chromosome sequence variation and the history ofhuman populations. Nat. Genet. 26:358–361.
WEALE, M. E., L. YEPISKOPOSYAN, R. F. JAGER, N. HOVHAN-NISYAN, A. KHUDOYAN, O. BURBAGE-HALL, N. BRADMAN,and M. G. THOMAS. 2001. Armenian Y chromosome hap-lotypes reveal strong regional structure within a single eth-no-national group. Hum. Genet. 109:659–674.
WILSON, I. J., and D. J. BALDING. 1998. Genealogical inferencefrom microsatellite data. Genetics 150:499–510.
WILSON, J. F., D. A. WEISS, M. RICHARDS, M. G. THOMAS, N.BRADMAN, and D. B. GOLDSTEIN. 2001. Genetic evidencefor different male and female roles during cultural transi-tions in the British Isles. Proc. Natl. Acad. Sci. USA 98:5078–5083.
WRIGLEY, E. A., and R. S. SCHOFIELD. 1989. The populationhistory of England. Cambridge University Press,Cambridge.
THE Y CHROMOSOME CONSORTIUM. 2002. A nomenclature sys-tem for the tree of human Y-chromosomal binary haplo-groups. Genome Res. 12:339–348.
EDWARD HOLMES, reviewing editor
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