Extinction: Bad Genes or Weak Chaos?

The dynamics of extinction and diversification of life is not a simple stochastic process, driven by random inputs. Biotic interactions are known to play a very important role in the population response to physical factors. In spite of this fact, it is not clear how the ecological scale is related with the macroevolutionary one. In this paper we suggest that both levels are, at least to some extent, decoupled. Using a simple model of large-scale evolution, we show how an $n$-species ecosystem evolves toward a critical state where extinctions of all sizes are generated. This state involves a situation where high unpredictability is present. The basic properties of the overall macroevolutionary pattern are well reproduced and a new interpretation for this process is suggested.