Comparison is fundamental to any evolutionary developmental analysis (e.g. Alberch 1985, Rieppel 1988, Dohle 1989, Minelli 2003, Scholtz 2005, Deutsch 2006, Jenner 2006, Breidbach and Ghiselin 2007). However, evo-devo as a discipline evolved from a mix of experimental and descriptive approaches to development. Accordingly, different weight is put on the method of studying development in an evolutionary framework depending on a researcher's scientific background. Here I want to evaluate the different approaches and their contribution to addressing evolutionary questions. I stress that only the comparative approach offers a direct method of studying development with respect to evolutionary changes. Descriptive and comparative approaches are often interpreted as being less ‘exact’ than experimental studies because they deal with untestable scenarios. Here I want to show that comparative approaches are a direct means to study evolution if the latter is accepted as the general framework for reasoning about causality and changes and the link between the two.