Systematic Review of the Research on Morphological Modularity

The modular organization of the phenotype is an emergent property that derives from a semi-independent relation of body parts in their inheritance, development, function, and evolution. Understanding the modular organization of living beings is essential to understand the evolvability and plasticity of organismal form, and how morphological variation is structured during evolution and development. For this reason, delimiting morphological modules and establishing the factors originating them is a lively field of inquiry in biology today. However, unifying the results of the available body of knowledge is a challenge because of the large number of species studied and the disparity of morphological system, from the flower of angiosperms to the wing of insects and the head of primates (to name a few). The specific factors behind each pattern of modularity and the methods used to identify vary widely as well. This review summarizes more than 190 original research articles since 1958, in order to get a quantitative appraisal on what is studied, how is studied, and how results are explained. The results reveal an heterogeneous picture, where some taxa, systems, and approaches are over-studied, while others receive minor attention; other major trends and gaps in the study of morphological modularity through time are also discussed. In sum, this systematic review seeks to offer an objective view of this research field and highlight future research niches.