 A basic presumption about model organisms is that they bear appropriate similarity relationships to larger groups of animals. This presumption is an instantiation of what is discussed generally for  models in science  meant to represent phenomena. Model organisms represent developmental phenomena in species that are either studied little or never studied at all: “we study flies and frogs as examples for the development of animals in general” (Nüsslein-Volhard 2006: 87). One source of confidence in treating them as exemplars derives from an inductive inference over discovered patterns of evolutionary conservation with respect to developmental phenomena (e.g., gastrulation or somite formation). If all or most model organisms share a developmental feature, then all or most animals will share the feature. This inference can be circumscribed more or less narrowly (e.g., if all or most vertebrate model organisms share somite formation, then all or most vertebrates will share it).