Species: Turning a Conundrum into a Research Program


  • Daniel R. Brooks
  • Deborah A. McLennan


evolutionary, species concept, historical ecology, phylogenetic species concept, phylogeny, speciation


The most appropriate ontological basis for understanding the role of species in evolutionary biology is the Evolutionary Species Concept. The ESC is not an operational concept, but one version of the Phylogenetic Species Concept is. Linking the ontology of species with the epistemological basis of actual biological studies requires that we specify both a discovery mode for identifying collections of organisms that we believe are evolutionary species, and a series of evaluation criteria for assessing those entities we have discovered. Simply naming a collection of specimens, no matter how strong one's evolutionary beliefs, is not sufficient for declaring that evolutionary species have been discovered. All operational historical species concepts represent discovery modes with minimal evaluation criteria; all operational non-dimensional species concepts represent evaluation criteria that do not specify discovery modes. Thus, both categories of knowledge are necessary and neither is sufficient for assigning species status. This leads naturally to a hierarchical research program in historical ecology, beginning with phylogenetic analysis of a group of entities postulated to be evolutionary species, which provides a productive arena for our arguments about species concepts.