"(…) the problem with contemporary evolutionary theory is not that its essential neo-Darwinian paradigm is incorrect. The problem is that the consistency argument of the synthesis (…) is itself troubled. That argument says that the core neo-Darwinian paradigm (the theory that deals with the origin, maintenance, and modification of within-population genetic structure) is consistent with all other known evolutionary phenomena. This credo, innocuous and undeniable as it is, has been expanded to mean that the neo-Darwinian paradigm of selection plus drift, are both necessary and sufficient to explain all other known evolutionary phenomena. My position here, and the position of all other doubters of the completeness of the synthesis that I know of, is simply that the neo-Darwinian paradigm is indeed necessary-but is not sufficient-to handle the totality of known evolutionary phenomena. And it may not even be necessary to explain certain particular phenomena. It is thus not a matter of either/or" Niles Eldredge (1985, p. 119) Unfinished Ontologies of the Modern Synthesis: The Hierarchical Structure of Nature and the Neglected Processes in Evolutionary Thought Written almost 35 years ago, the words of Niles Eldredge that we chose as our epigraph still resonate in the contemporary landscape of evolutionary biology (see Laland et al. 2014; Love 2017). As has been claimed many times (e.g. in Wagner 2014), the ontology and language of population genetics, the explanatory heart of the Modern Synthesis (MS), are far too limited and abbreviated to capture Abstract Contemporary evolutionary biology comprises a plural landscape of multiple co-existent conceptual frameworks and strenuous voices that disagree on the nature and scope of evolutionary theory. Since the mid-eighties, some of these conceptual frameworks have denounced the ontologies of the Modern Synthesis and of the updated Standard Theory of Evolution as unfinished or even flawed. In this paper, we analyze and compare two of those conceptual frameworks, namely Niles Eldredge's Hierarchy Theory of Evolution (with its extended ontology of evolutionary entities) and the Extended Evolutionary Synthesis (with its proposal of an extended ontology of evolutionary processes), in an attempt to map some epistemic bridges (e.g. compatible views of causation; niche construction) and some conceptual rifts (e.g. extra-genetic inheritance; different perspectives on macroevolution; contrasting standpoints held in the "externalism-internalism" debate) that exist between them. This paper seeks to encourage theoretical, philosophical and historiographical discussions about pluralism or the possible unification of contemporary evolutionary biology.