According to the H-Evo-Devo Theory, megaevolution belongs to the higher taxa level, and modular-evolution pertains to the homologue level. This chapter explores the biological processes surrounding the origin, stability, and extinction of higher taxa as well as the origin and stability of homologues as modules of comparative anatomy. Concerning the origin of higher taxa, the taxonomic structure in which they arise is built from the top-down, i.e., higher-level body plans originate first, followed sequentially by lower-level body plans. Additionally, the sudden origin of these entities at various taxonomic ranks (as hopeful monsters) is highlighted. Regarding stability, higher taxa exhibit supraspecific stasis, a phenomenon described in other studies under the term “living fossils,” which is explained by developmental constraints. With respect to higher taxa extinction, this process results from mass extinctions and the loss of parts. Meanwhile, modules are produced through the phenomenon of co-option, and the cause of their stability is attributed to developmental constraints acting at the deepest level of the hierarchy. Overall, this chapter specifically emphasizes the biological causes at higher levels of the hierarchy.