Tree thinking and species delimitation: Guidelines for taxonomy and phylogenetic terminology

By tradition, phylogenetic trees are presented in such a way that species-poor taxa are placed on the left side and their more diverse sister taxa on the right (usually with humans on the far right). This often leads to reading the tree as a “ladder of progress” from left (allegedly primitive, basal or even ancestral) to right (allegedly advanced, derived, descendant). Although biologically and logically wrong and often bemoaned, the evolutionary literature teems with language perpetuating this phylogenetic misconception. Likewise, the splitting of one into two or more species based on different versions of the Phylogenetic Species Concept has recently found a growing number of adherents, resulting, in the eyes of many, in a trivialization of the species category (“taxonomic inflation”). This editorial briefly summarizes these phylogenetic and taxonomic issues and provides guidelines to authors submitting their studies to Mammalian Biology in order to avoid errors in phylogenetic discussions and to do justice to the fundamental nature of species in biology.