According to Gregory Clark, because of regression to the mean and the lack of any (e.g., racial) barrier preventing gene flow across classes, there was never a persistent ruling class in England.
Notes from a presentation by Clark last year containing "work in progress from a planned book on social mobility over the long run" (pdf):
What is the fundamental nature of human society? Is it stratified into enduring
layers of privilege and want, with some mobility between the layers, but permanent
social classes? Or is there, over generations, complete mobility between all ranks in
the social hierarchy, and complete long run equal opportunity? [. . .]
This book systematically exploits a new method of tracing social mobility over
many generations, surnames, to measure the persistence of classes over as much as
800 years, 24 generations. It looks at societies where surnames are inherited,
unchanged, by children from fathers. In such cases they thus serve as a tracer of the
distant social origins of the modern population (and interestingly also as a tracer of
the Y chromosome).
In this role surnames are a surprisingly powerful instrument for measuring long
run social mobility. The results they reveal are clear, powerful, and a shock to our
casual intuitions.
(1) In England, where we can trace social mobility back to 1066 using surnames,
there were never any long persistent ruling and lower classes for the indigenous
population: not in medieval England, and not now. About 5-6 generations were, and
are, enough to erase most echoes of initial advantage or want. For the English class
is, and always was, an illusion. Histories such as those of the Stanley family turn out
to be rare exceptions, not the rule.
(2) Paradoxically, while England reveals complete long run mobility, the rates of
social mobility per generation, better measured by looking over multiple generations,
turn out to be lower than is conventionally estimated. But the mathematics of
mobility is such that even such slow regression to the mean, over time, will
completely erase initial advantage and want.
(3) The rate of social mobility in England was as high in the middle ages as it is now.
The arrival of the whole apparatus of free public education in the late nineteenth century, and the elimination of nepotism in government and private firms, has not
improved the rate of social mobility.
(4) The extraordinarily complete long run mobility of England is likely typical of
other western European societies. But other countries, in contrast, do exhibit
persistent social classes over hundreds of years. In the US, for example, the Black
population has persisted at the bottom of the social order, and the Jewish population
at the top. In Chile surname evidence shows the indigenous population has
remained at the bottom since the Spanish conquest of 1541. [. . .]
(7) Though parents at the top of the economic ladder in any generation in preindustrial
England did not derive any lasting advantage for their progeny, there was
one odd effect. Surname frequencies show was that there was a permanent increase
in the share of the DNA in England from rich parents before 1850. After 1850 a
frequency effect operated, but in reverse. Surname frequencies show the DNA share
of families in England who were rich in 1850 declined relative to that of poor
families of the same generation by 2010. [. . .]
What is the meaning and explanation of these results? This is a much more
contentious and difficult area. The book argues for the following conclusions:
A. Why can’t the ruling class in a place like England defend itself against downwards
mobility? If the main determinants of economic and social success were wealth,
education and connections then there would be no explanation of the consistent
tendency of the rich to regress to the society mean. Only if genetics is the main
element in determining economic success, if nature trumps nurture, is there a built-in
mechanism that ensures the observed regression. That mechanism is the
intermarriage of the rich with those from the lower classes. Even though there is
strong assortative mating, since this is based on the phenotype created in part by
chance and luck, those of higher than average innate talent tend to systematically
mate with those of lesser ability and regress to the mean.
B. Racial, ethnic and religious differences allow long persisting social stratification
through the barriers they create to this intermarriage. Thus for a society to achieve
complete social mobility it must achieve cultural homogeneity. Multiculturalism is
the enemy of long run equality.
On the Normans:
