Class is something that 95%
of Americans don't understand at all. Yet it is one of the most
important global forces acting on humans.
Class dates back to the the cloudy mist of human social formation. The first emperor kings surrounded themselves with a class of people who were loyal to them. Together, this comprised the top social class. The people in this top class were invariably family members or members of families associated with the paramount ruling figure. The ruler and the coterie of close associates were the top social class in virtually all societies that were based on agriculture. (There were a few exceptional societies such as the Vikings.)
This coterie of the select at the top of society were nearly always members of their class by birth. This top social class was an inherited class. The inherited top class still exists nearly everywhere in the world today. The most blatant exception is the U.S.
There
is an inherited top class in England today, where I've spent plenty of
time and France as well (it remains in the British colonies including
Canada). In both England and France members of the top class are
usually taller than the rest of the society; this class has myriad
privileges in clubs, entrance to top schools and priority in government
and corporate positions. The same is true in nearly every society I
know including the rest of Europe, Russia, Latin America and India.
The societies that have great social mobility and weak social class are
Holland, Denmark, Sweden, Israel and Japan. I don't know about
several others such as Finland and Mongolia. Arab and Persian societies
are tribal with one tribe at the top for long periods. China is built
on extended families with one on the top.
There is no theory of social class necessary other than one that recognizes the top inherited social class. Most hierarchical national social structures below the top are culturally specific such as India's. Some hierarchical social structures below the top are volatile to a degree, such as Poland's and some are unstable over long periods such as Burma's.