  In a laboratory experiment, round by round, individual interactions should
lead to the social evolutionary rotation in population strategy state space.
Successive switching the incentive parameter should lead to successive change
of the rotation ---- both of its direction and its strength. In data from a
switching payoff matrix experiment of extended 2x2 games (Binmore, Swierzbinski
and Proulx, 2001 [1]), we find the changing of the social evolutionary rotation
can be distinguished quantitatively. The evolutionary rotation can be captured
by evolutionary dynamics. With eigenvalue from the Jacobian of a constrained
replicator dynamics model, an interpretation for observed rotation strength is
given. In addition, equality-of-populations rank test shows that relative
response coefficient of a group could persist cross the switching parameter
games. The data has successively been used to support Von Neumann's minimax
theory. Using the old data, with observed evolutionary rotation, this report
provides a new insight into evolutionary game theory and experimental social
dynamics.
