A model of evolution

The theory of evolution is too general to be able to make predictions. However, like every other hypergeneral scientific theory, it can be enriched with specific assumptions and data, and thus become a specific model for a particular evolutionary line. This paper exhibits such a model. It accounts for the evolution of a biopopulation in terms of genetic and environmental variables. The results is a system of linear finite difference equations that enable one to pin down the necessary and sufficient conditions for evolution proper to occur, as well as to predict the average numbers of the final varieties originating from the parent population. It is estimated that the main value of the paper is methodological rather than substantive, in that it suggests a way of building models of biological lineages.