Under the conditions prevalent in the late Pleistocene epoch (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. The transition from an egalitarian society
and the acceptance of the new institutions may have been possible only
if, 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 a new social crisis. Using a simple model
inspired by previous work by Bowles and Gintis, these effects are studied
here