Of all the taxonomic ranks species is the most clear, distinct, and concrete. More practically, it is the level which most naturally falls out of the patterns of life’s tree. Or does it? If the term “species concept” does not ring a bell, please see this entry. If it does, how do you define species in a non-arbitrary manner?
John Hawks and Jerry Coyne are mooting the ‘species concepts’ debate, with particular focus on recent human origins (specifically, the relationship of modern humans to Neandertals and Denisovans). Coyne, who coauthored the book Speciation and remains preoccupied with the issue in his academic work, knows of what he speaks. And of course he wouldn’t think that the discussion of species, how to delineate them, and what they are, is a sterile exercise. He has chosen to allocate a significant portion of his life to the topic. I think very few would disagree with Coyne when he contends that “Species are not arbitrary divisions of an organic continuum.” If there is one taxonomic category which has a concrete basis in reality, that would seem to be species. But, I would observe that I’m not sure that species are necessarily so clear and distinct. After all, we know that there is here and there, but where does here end, and there begin?
I’m of a reminded of the classic Zeno’s paradox: