A simply physical model of biological evolution of an ecology of interacting species is introduced. The model self-organizes into a critical steady state with intermittent coevolutionary explosions and exhibits the ‘‘punctuated equilibrium’’ phenomenon. The dynamics of the model markedly differs from that of an earlier (and simpler) one of Bak and Sneppen [Phys. Rev. Lett. 71, 4083 (1993)], but allows for similar conclusions, which allows one to speculate about their universality.

• Received 8 June 1995

DOI:https://doi.org/10.1103/PhysRevE.52.5700