Recent experimental results with humans involved in social dilemma games
suggest that cooperation may be a contagious phenomenon and that the selection
pressure operating on evolutionary dynamics (i.e., mimicry) is relatively weak.
I propose an evolutionary dynamics model that links these experimental findings
and evolution of cooperation. By assuming a small fraction of (imperfect)
zealous cooperators, I show that a large fraction of cooperation emerges in
evolutionary dynamics of social dilemma games. Even if defection is more
lucrative than cooperation for most individuals, they often mimic cooperation
of fellows unless the selection pressure is very strong. Then, zealous
cooperators can transform the population to be even fully cooperative under
standard evolutionary dynamics.Comment: 5 figure
