Emergence of Modularity in Biology

Complex systems are often organized in terms of simpler subsystems, or modules; how this occurs in Nature is an interesting question. Biological organisms evolve in a changing environment, and I will show that the level of modularity correlates with the rapidity and severity of environmental change. Emergence of modularity is driven by noise in the environment and is facilitated by mechanisms like horizontal gene transfer; this is evident from viruses and bacteria to development and physiology. Bacterial metabolic networks show increasing modularity as the environment changes or the horizontal gene transfer rate increases; experimental protein interaction data shows that protein networks have become increasingly modular over the last four billion years. More recently, modularity provides early warnings in the evolution of influenza flu strains and in heart rate anomalies in physiology.