We consider two, apparently similar, models of biological evolution that have been claimed to exhibit self-organized critical behavior. A careful reanalysis of these models, including several analytic results for one of them, suggests that they are qualitatively different. We demonstrate the limitations of the mean field description of these systems. We argue that a more precise definition of self-organized criticality is desirable and establish several criteria in this connection.

• Received 16 September 1994

DOI:https://doi.org/10.1103/PhysRevE.51.1059