Response to criticisms of an updated subspecies concept

Abstract

In an attempt to resolve some contemporary controversies about the taxonomy of incompletely separated lineages, I recently proposed an updated concept of subspecies (de Queiroz 2020). According to that updated concept, subspecies are entities of the same fundamental kind as species (separately evolving metapopulation lineages) that differ from other entities considered species only in that they are incompletely separated from one another and therefore are parts of a more inclusive species (lineage). This updated concept of subspecies not only resolves various controversies about the taxonomy of incompletely separated lineages, it also brings the concept of subspecies into congruence with a unified concept of species, gives the concept of subspecies a biologically meaningful definition, and ends the treatment of the subspecies category as an artificial taxonomic rank. Despite these benefits, this new concept of subspecies is at odds with certain taxonomic traditions, and therefore I anticipated that it would meet resistance. In this context, it is not surprising that a criticism of my proposal has recently been published by Hillis (2021). Here I respond to that criticism to clarify both the nature of my proposal and why it is preferable to retaining a more traditional concept of subspecies.