Facing permanent taxonomic change

Four major taxonomic revisions published between 1982 and 2020 brought the total number of recognized mammalian species from the initial 4,629 species to the current 6,554 species, i.e. an astonishing increase of 57% in merely 38 years.Closer look at these lists shows that the estimate in each next edition is not merely the number in the previous issue with the addition of new discoveries in the interim period.Frequently, species are split through gain of new evidence which is not surprising given that taxonomic decisions are hypotheses rather than the reality itself.It comes more as a surprise that two globally used lists from 2020 reported widely different estimates: 5,899 species in the IUCN Red list versus the already quoted 6,554 species in the Checklist of the Mammals of the World.To make confusion even worse, experts involved in zoological systematics in general and species delimitation in particular take quite a variety of positions about the defining properties of a species.Over thirty species concepts are currently in circulation, each defining the species in at least slightly different ways.This may come as a surprise given that species are believed to be one of the fundamental units of biological organization underpinning every discipline of biology.Indeed, species lists have a wide range of users who have little time, interest or knowledge to interpret intelligently the results of taxonomic labour.The instability of taxonomic names is therefore perplexing to them, even more so when such changes are seemingly unnecessary.