NOT fractals or chaos theory, what theory explains group behavior based on tiny individual decisions?

I'm looking for info but can't remember the name for this idea about the seeming intelligence of a large group of individual's behavior can be understood by looking at each individual's decision. I think it dovetails into fractal study, chaos theory and some Rupert Sheldrake ideas. Thanks for help, especially links!|||Check out Philip Zimbardo, one of the pioneers of group behavior study.|||Game theory.