Near decomposability and the speed of evolution

This paper proposes an explanation for a fundamental property that appears to be shared by all multicelled organisms. Such organisms consist of a hierarchy of components, such that, at any level of the hierarchy, the rates of interaction within components at that level are much higher than the rates of interaction between different components. Systems with this property are called nearly completely decomposable, or more briefly, nearly decomposable (ND). The explanation for the ubiquity of the ND property is that, under the usual conditions of mutation and/or crossover and natural selection, ND systems will increase in fitness, and therefore reproduce, at a much faster rate than systems that do not possess the ND property.