Unraveling the specific spirit which animated some seminal works in the first half of the twentieth century could increase our understanding of the contemporary diversity of theoretical biologies and, more generally, of the biological studies which are based on theoretical models, especially as far as growth and morphogenesis are concerned. Going back to the main epistemological ideas of d’Arcy Thompson, Lotka, Woodger, Rashevsky and Rosen, this chapter follows a historical, epistemological but also comparative line. Its guiding questions are the following: to what extent can one say that there was and there still exists a diversity of mathematical biologies, but also a diversity of biophysics and theoretical biologies? In what precise terms nonetheless can we formulate the core problem that all theoretical biologies have to solve - whatever their diversity? How each of these diverse approaches leads us to conceive the nature of the complexities of life? And, how accordingly, does each one lead us to think the epistemic role of theorizing and modeling once it has assumed for itself the very nature and origin of these complexities?