On Price's equation and average fitness

A number of recent discussions have argued that George Price's equation for representing evolutionary change is a powerful and illuminating tool, especially in the context of debates about multiple levels of selection. Our paper dissects Price's equation in detail, and compares it to another statistical tool: the calculation and comparison of average fitnesses. The relations between Price's equation and equations for evolutionary change using average fitness are closer than is sometimes supposed. The two approaches achieve a similar kind of statistical summary of one generation of change, and they achieve this via a similar loss of information about the underlying fitness structure.