Evolution of modularity in biological networks*

At each scale of organization, living systems are composed of subsets of elements that interact closely with each other, forming modules that behave in turn as more complex elements of systems at higher levels of organization. For example, cells can be viewed as modular components that self-organize into organisms, and organisms as modules that interact to form ecologies. Understanding the underlying processes that can produce such modularity could help explain why evolution tends to form increasingly complex structures and dynamics. So far, however, we know very little about the origins of modularity in living systems.

In this work, we show that modular organization can emerge spontaneously in Boolean networks that mimic biological systems, if these are subjected to changing environmental conditions in an evolutionary process that can involve, both, the Boolean dynamical rules and the network topology. We find that modularity provides adaptive advantages that increase the effective fitness and identify the mechanisms that lead to its emergence. These analyses could provide insights into why living systems appear to favor modular structures and dynamics at all scales.