What is modularity?

Modularity is a quite general organizational pattern, and it’s a useful concept in several different areas, from computer science to biology. In biology, the concept is applied at practically every level or organization, from the structure of macro-molecules (Ancel and Fontana’s classic paper¹ is probably my favorite on this subject), to ecological communities.² The basic premise is the same in all these flavors of modularity: a system is modular if its constitutive elements are organized into semi-independent groups, called modules, that are internally strongly connected, leading to a internal coherence of the modules and a relative independence between modules. Influenced by Tiago, I’ve recently taken to calling these modules assortative³, to differentiate them from other possibilities for parceling elements into groups.