  The occurrence of discrimination is an important problem in the social and
economical sciences. Much of the discrimination observed in empirical studies
can be explained by the theory of in-group favoritism, which states that people
tend to act more positively towards peers whose appearances are more similar to
their own. Some studies, however, find hierarchical structures in inter-group
relations, where members of low-status groups also favor the high-status group
members. These observations cannot be understood in the light of in-group
favoritism. Here we present an agent based model in which evolutionary dynamics
can result in a hierarchical discrimination between two groups characterized by
a meaningless, but observable binary label. We find that discriminating
strategies end up dominating the system when the selection pressure is high,
i.e. when agents have a much higher probability of imitating their neighbor
with the highest payoff. These findings suggest that the puzzling persistence
of hierarchical discrimination may result from the evolutionary dynamics of the
social system itself, namely the social imitation dynamics. It also predicts
that discrimination will occur more often in highly competitive societies.
