Turrill’s Omega: A Heuristic Index for Quantifying the Support of a Taxonomic Hypothesis

Abstract

Biological research relies on the use of taxa, with species expressed in the form of a Latin binomial. Although taxa are commonly regarded as established entities, they actually represent hypotheses on the distribution of natural biological variation and may change their status as new systematic knowledge becomes available. A long-standing problem affecting systematics and taxonomy, with important consequences for other biological disciplines, is that a binomial itself conveys no information about the strength of the taxonomic hypothesis it represents. Here, we introduce the concept of a standardized heuristic index, named Turrill’s Omega Index (TOI), to estimate the degree of support for a taxonomic hypothesis. Turrill’s Omega Index is a single numerical value calculated by integrating four macro-categories of comparative data: Phenotype, Genealogy, Isolation, and Geography-Ecology. Turrill’s Omega Index provides a practical and reliable framework for quantifying the support for a taxonomic hypothesis, without requiring resolution of the long-standing debate surrounding species delimitation and species concepts. Accordingly, it has the potential to represent a valuable and transformative advance in systematics and taxonomy. In addition, TOI can support conservation decision-making by helping prioritize funding allocation among equally threatened taxa according to their degree of support.