Beyond formal equivalence: research questions and explanatory function in group and multilevel selection theory

The debate over group and multilevel selection remains central to evolutionary biology, particularly in explanations of cooperation and social evolution. A persistent issue is whether group- and multilevel-selection models and kin-selection formulations are formally equivalent, that is, whether they can represent the same evolutionary change under specified assumptions, and what follows from such equivalence for explanation. We conducted a systematic review and thematic synthesis of 94 model-centered studies, characterized by explanatory orientation, Research Question, multilevel selection I/II classification, formal tool, decomposition role, causal interpretation, and equivalence claims. Explanatory orientations were heterogeneous, and formal-tool use overlapped substantially across them. Associations involving decomposition role weakened in sensitivity analyses, while predominant Research Question showed no detectable association with multilevel selection I/II classification. Among the 68 studies that substantively discussed equivalence, qualified positions predominated and categorical rejection was rare; most addressed multiple objects of equivalence. These results indicate that explanatory orientation, Research Questions, formal representations, causal interpretation, and equivalence claims are related but non-interchangeable dimensions of the debate. Formal equivalence can establish genuine relations between representations without determining that they identify the same causal structure, serve the same explanatory function, or support the same attribution of adaptation. Persistent disagreement is therefore better understood as concerning what formal translations preserve, which biological questions they answer, and what explanatory conclusions follow from them.