  Hierarchical networks are prevalent in nature and society, corresponding to
groups of actors - animals, humans or even robots - organised according to a
pyramidal structure with decision makers at the top and followers at the
bottom. While this phenomenon is seemingly universal, the underlying governing
principles are poorly understood. Here we study the emergence of hierarchies in
groups of people playing a simple dot guessing game in controlled experiments,
lasting for about 40 rounds, conducted over the Internet. During the games, the
players had the possibility to look at the answer of a limited number of other
players of their choice. This act of asking for advice defines a directed
connection between the involved players, and according to our analysis, the
initial random configuration of the emerging networks became more structured
overt time, showing signs of hierarchy towards the end of the game. In
addition, the achieved score of the players appeared to be correlated with
their position in the hierarchy. These results indicate that under certain
conditions imitation and limited knowledge about the performance of other
actors is sufficient for the emergence of hierarchy in a social group.
