EXTINCTION AND SELF-ORGANIZED CRITICALITY IN A MODEL OF LARGE-SCALE EVOLUTION

A simple model of large-scale biological evolution is presented. This model involves an N-species system where interactions take place throu gh a given connectivity matrix, which can change with time. True extin ctions, with removal of less-fit species, occur followed by episodes o f diversification. An order parameter may be naturally defined in the model. Through the dynamical equations, the system moves towards the c ritical threshold, which triggers the extinctions. The frequency distr ibution N(s) of extinctions of size s follows a power law N(s)approxim ate to s-alpha With alpha approximate to 2.3, close to known palaeobio logical evidence.