  Under the conditions prevalent in the late Pleistocene (small hunter-gatherer
groups and frequent inter-group conflicts), coevolution of gene-related
behavior and culturally transmitted group-level institutions provides a
plausible explanation for the parochial altruistic and reciprocator traits of
most modern humans. When, with the agricultural revolution, societies became
larger and more complex, the collective nature of the monitoring and punishment
of norm violators was no longer effective. This led to the emergence of new
institutions of governance and social hierarchies. Likely, the smooth
acceptance of the new institutions was possible only because, in the majority
of the population, the reciprocator trait had become an internalized norm.
However the new ruling class has its own dynamics which in turn may lead to new
social crisis. Using a simple model, inspired on previous work by Bowles and
Gintis, these effects are studied here.
