  A class of models for large-scale evolution and mass extinctions is
presented. These models incorporate environmental changes on all scales, from
influences on a single species to global effects. This is a step towards a
unified picture of mass extinctions, which enables one to study coevolutionary
effects and external abiotic influences with the same means. The generic
features of such models are studied in a simple version, in which all
environmental changes are generated at random and without feedback from other
parts of the system.
