 Once these types of developmental mechanisms have been distinguished, several conceptual issues become salient. The first pertains to how the two types of mechanisms are interrelated during ontogeny, and how different investigative approaches do or do not successfully provide integrated accounts of them  (Section 3.3).  A second is their distinct patterns of generality. Molecular genetic mechanisms are widely conserved across phylogenetically disparate taxa as a consequence of evolutionary descent, whereas cellular-physical mechanisms are widely instantiated as a consequence of shared physical organization but not due to evolutionary descent (Love 2017a). The divergence of these patterns has prompted explicit epistemological reflection by developmental  biologists.[3]