Introduction
The role of migration in the Anglo-Saxon transition in England remains controversial.
Archaeological and historical evidence is inconclusive, but current estimates of the
contribution of migrants to the English population range from less than 10000 to as
many as 200000. In contrast, recent studies based on Y-chromosome variation posit
a considerably higher contribution to the modern English gene pool (50-100%).
Historical evidence suggests that following the Anglo-Saxon transition, people of
indigenous ethnicity were at an economic and legal disadvantage compared to
those having Anglo-Saxon ethnicity. It is likely that such a disadvantage would lead
to differential reproductive success. We examine the effect of differential
reproductive success, coupled with limited intermarriage between distinct ethnic
groups, on the spread of genetic variants. Computer simulations indicate that a
social structure limiting intermarriage between indigenous Britons and an initially
small Anglo-Saxon immigrant population provide a plausible explanation of the high
degree of Continental male-line ancestry in England.
The arguments of the articles
From figure 1 it can be seen that under a range of plausible combinations of selective advantage
to being Anglo-Saxon and intermarriage rate (see below), the proportion of ‘immigrant’ Y-
chromosomes rises from 20% or less immediately following migration to greater than 50% in 15
generations. We consider 50% to be a conservative estimate of the proportion of Y-chromosomes
in the present-day English gene pool that originate among Anglo-Saxon migrants in the fifth
century (Weale et al. 2002; Capelli et al. 2003). Fifteen generations marks the upper limit for the
duration of an Anglo-Saxon/British apartheid-like social structure since, by assuming an
intergenerational time of between 25 and 30 years, this is the approximate time span between the
initial immigration in the middle of the fifth century and the laws of Alfred the Great (issued
around AD 890), which do not contain any indications of legal status differences between
Britons and Anglo-Saxons (Whitelock 1979). Although others have reported a male-specific
intergeneration time of around 35 years (Tremblay & Vezina 2000), this estimate is based on
genealogical records from a rapidly growing population between the seventeenth and the
twentieth centuries. We reason that in Anglo-Saxon England, life expectancy, and as a
consequence, intergeneration time would be shorter. However, 15 generations cannot be
considered as a conservative estimate of the duration of such an apartheid-like social structure.
For this reason we also examined the rate of increase in the proportion of ‘immigrant’ Y-
chromosomes over time under a range of parameter values (figure 2). The proportion of
‘immigrant’ Y-chromosomes rises rapidly at first then levels off to its ceiling value. It is notable
that the time taken to reach a near-ceiling value is largely determined by the reproductive
parameter and is relatively unaffected by the intermarriage rate, although the ceiling value itself
is strongly affected by the by the intermarriage rate. Most importantly, the proportion of
‘immigrant’ Y-chromosomes can rise from 10% to in excess of 50% in considerably fewer than
15 generations under plausible parameter values. This is best illustrated in figure 3, where we
have explored the effects of different parameter values on the number of generations required to
reach 50% ‘incoming’ Y-chromosomes in the whole population. Comparing figure 3a–
, c (representing 5, 10 and 20% Anglo-Saxon migration, respectively), it is evident that the initial
size of the migration is a highly influential parameter here.
The model we present is necessarily simple but serves to illustrate some of the effects of
differential reproductive success among groups, with a degree of reproductive isolation, on
patterns genetic variation (Woolf 2004). We have only presented the results of simulations
assuming symmetric intermarriage rates (U=D, see §2). We also tested asymmetric intermarriage
rates whereby we multiplied U by 0.5 and D by 1.5 or vice versa and obtained very similar
results to those presented (data not shown; figures available from the authors).
We reason that an apartheid-like social structure is a likely outcome of the Anglo-Saxon
immigration into post-Roman Britain on theoretical and evidential grounds. The theoretical
argument derives from the migration context and the relative sizes of the two groups. The
immigration led to an encounter of two blocks of different ethnic groups with different, mutually
incomprehensible languages (Celtic and some Latin on the part of the natives, Germanic
languages on the part of the immigrants) and probably rather different degrees of social
complexity and military mobilization (the native population having been largely unarmed and
untrained in Roman times). At the same time, the natives are likely to have been in the majority:
current population estimates for late third-century Roman Britain are as high as 3.7 million
(Millett 1990), and allowing for a population decline in the fourth and early fifth century, one
would still have to assume a native population in the region of 2 million. By contrast, estimates
for migrating populations in the early middle ages are between tens and low hundreds of
thousands; for example, Heather (1991) has estimated that the Ostrogoths moving from the
Balkans into Italy in the late fifth century numbered more than 100 000. As a consequence, the
minority immigrants faced the danger of losing their identity and their political and military
control by assimilating in the much larger autochtonous population. The imposition of an
apartheid-like social structure is one of the strategies open to a dominant ethnic minority, and it
is one which is historically and ethnographically documented under such conditions (Thurnwald
1931).
The evidential argument rests on a textual source and some skeletal evidence. The laws of Ine,
the late seventh-century ruler of the Anglo-Saxon kingdom of Wessex, distinguish clearly
between Saxons and ‘Welsh’ (native Britons) and accord them different legal status even though
the laws imply that the two groups live in close proximity, and often under the same roof
(Whitelock 1979). Such a distinction is unlikely to have arisen in the seventh century, two
centuries after the initial contact. It is much more likely to have originated in the immigration
situation of the fifth and early sixth centuries. On the other hand, this ethnic distinction of two
intermingling populations and its formalization in law cannot have survived for such a long
period without some mechanism that perpetuated the distinction. Physical segregation could have
this effect, but this is not what the laws of Ine imply; therefore an apartheid-like social structure
seems to be the most obvious mechanism.
Skeletal evidence for the existence of two populations that are to an extent reproductively
isolated is more circumstantial, and rests on the stature differential between men buried with, and
those buried without weapons in cemeteries of Anglo-Saxon England. Men with weapons (47%
of male adults) have been suggested, on a number of archaeological and skeletal indicators, to be
immigrants and descendants of immigrants, while men without weapons (53%) are a more
disparate group that appears to include a sizeable proportion of native Britons (Härke
The role of migration in the Anglo-Saxon transition in England remains controversial.
Archaeological and historical evidence is inconclusive, but current estimates of the
contribution of migrants to the English population range from less than 10000 to as
many as 200000. In contrast, recent studies based on Y-chromosome variation posit
a considerably higher contribution to the modern English gene pool (50-100%).
Historical evidence suggests that following the Anglo-Saxon transition, people of
indigenous ethnicity were at an economic and legal disadvantage compared to
those having Anglo-Saxon ethnicity. It is likely that such a disadvantage would lead
to differential reproductive success. We examine the effect of differential
reproductive success, coupled with limited intermarriage between distinct ethnic
groups, on the spread of genetic variants. Computer simulations indicate that a
social structure limiting intermarriage between indigenous Britons and an initially
small Anglo-Saxon immigrant population provide a plausible explanation of the high
degree of Continental male-line ancestry in England.
The arguments of the articles
From figure 1 it can be seen that under a range of plausible combinations of selective advantage
to being Anglo-Saxon and intermarriage rate (see below), the proportion of ‘immigrant’ Y-
chromosomes rises from 20% or less immediately following migration to greater than 50% in 15
generations. We consider 50% to be a conservative estimate of the proportion of Y-chromosomes
in the present-day English gene pool that originate among Anglo-Saxon migrants in the fifth
century (Weale et al. 2002; Capelli et al. 2003). Fifteen generations marks the upper limit for the
duration of an Anglo-Saxon/British apartheid-like social structure since, by assuming an
intergenerational time of between 25 and 30 years, this is the approximate time span between the
initial immigration in the middle of the fifth century and the laws of Alfred the Great (issued
around AD 890), which do not contain any indications of legal status differences between
Britons and Anglo-Saxons (Whitelock 1979). Although others have reported a male-specific
intergeneration time of around 35 years (Tremblay & Vezina 2000), this estimate is based on
genealogical records from a rapidly growing population between the seventeenth and the
twentieth centuries. We reason that in Anglo-Saxon England, life expectancy, and as a
consequence, intergeneration time would be shorter. However, 15 generations cannot be
considered as a conservative estimate of the duration of such an apartheid-like social structure.
For this reason we also examined the rate of increase in the proportion of ‘immigrant’ Y-
chromosomes over time under a range of parameter values (figure 2). The proportion of
‘immigrant’ Y-chromosomes rises rapidly at first then levels off to its ceiling value. It is notable
that the time taken to reach a near-ceiling value is largely determined by the reproductive
parameter and is relatively unaffected by the intermarriage rate, although the ceiling value itself
is strongly affected by the by the intermarriage rate. Most importantly, the proportion of
‘immigrant’ Y-chromosomes can rise from 10% to in excess of 50% in considerably fewer than
15 generations under plausible parameter values. This is best illustrated in figure 3, where we
have explored the effects of different parameter values on the number of generations required to
reach 50% ‘incoming’ Y-chromosomes in the whole population. Comparing figure 3a–
, c (representing 5, 10 and 20% Anglo-Saxon migration, respectively), it is evident that the initial
size of the migration is a highly influential parameter here.
The model we present is necessarily simple but serves to illustrate some of the effects of
differential reproductive success among groups, with a degree of reproductive isolation, on
patterns genetic variation (Woolf 2004). We have only presented the results of simulations
assuming symmetric intermarriage rates (U=D, see §2). We also tested asymmetric intermarriage
rates whereby we multiplied U by 0.5 and D by 1.5 or vice versa and obtained very similar
results to those presented (data not shown; figures available from the authors).
We reason that an apartheid-like social structure is a likely outcome of the Anglo-Saxon
immigration into post-Roman Britain on theoretical and evidential grounds. The theoretical
argument derives from the migration context and the relative sizes of the two groups. The
immigration led to an encounter of two blocks of different ethnic groups with different, mutually
incomprehensible languages (Celtic and some Latin on the part of the natives, Germanic
languages on the part of the immigrants) and probably rather different degrees of social
complexity and military mobilization (the native population having been largely unarmed and
untrained in Roman times). At the same time, the natives are likely to have been in the majority:
current population estimates for late third-century Roman Britain are as high as 3.7 million
(Millett 1990), and allowing for a population decline in the fourth and early fifth century, one
would still have to assume a native population in the region of 2 million. By contrast, estimates
for migrating populations in the early middle ages are between tens and low hundreds of
thousands; for example, Heather (1991) has estimated that the Ostrogoths moving from the
Balkans into Italy in the late fifth century numbered more than 100 000. As a consequence, the
minority immigrants faced the danger of losing their identity and their political and military
control by assimilating in the much larger autochtonous population. The imposition of an
apartheid-like social structure is one of the strategies open to a dominant ethnic minority, and it
is one which is historically and ethnographically documented under such conditions (Thurnwald
1931).
The evidential argument rests on a textual source and some skeletal evidence. The laws of Ine,
the late seventh-century ruler of the Anglo-Saxon kingdom of Wessex, distinguish clearly
between Saxons and ‘Welsh’ (native Britons) and accord them different legal status even though
the laws imply that the two groups live in close proximity, and often under the same roof
(Whitelock 1979). Such a distinction is unlikely to have arisen in the seventh century, two
centuries after the initial contact. It is much more likely to have originated in the immigration
situation of the fifth and early sixth centuries. On the other hand, this ethnic distinction of two
intermingling populations and its formalization in law cannot have survived for such a long
period without some mechanism that perpetuated the distinction. Physical segregation could have
this effect, but this is not what the laws of Ine imply; therefore an apartheid-like social structure
seems to be the most obvious mechanism.
Skeletal evidence for the existence of two populations that are to an extent reproductively
isolated is more circumstantial, and rests on the stature differential between men buried with, and
those buried without weapons in cemeteries of Anglo-Saxon England. Men with weapons (47%
of male adults) have been suggested, on a number of archaeological and skeletal indicators, to be
immigrants and descendants of immigrants, while men without weapons (53%) are a more
disparate group that appears to include a sizeable proportion of native Britons (Härke
