Multilevel selection in a broader hierarchical perspective

Since Darwin, multilevel selection has been the key concept of the hierarchical approach to evolution. The debate around the significance of group selection as an evolutionary phenomenon (in both an early controversial version and subsequent mathematical definition) has been the main entrance to multilevel selection theories. We present here a historical sketch of the debate prior to the formalization proposed by Samir Okasha. We also consider two extensions of Okasha’s multilevel theory: the diachronic perspective made possible by the study of major evolutionary transitions; the cross-level exaptive by-products. The double hierarchy, first proposed by Niles Eldredge and Stanley Salthe is a different kind of multilevel approach to evolution that avoids some theoretical impasses produced by a strictly selection-centered approach to extend the levels of evolutionary change. We argue that a dual hierarchical approach has a major heuristic power in order to embrace the complexity of evolutionary phenomena, from molecules to ecosystems, and is a candidate for an updated and unifying meta-theory of evolutionary patterns.