ABSTRACT
The word species has a historic resonance. Entities of all kinds fall into nested categories: gold is a metal and a chemical element. It would be correct to say that you are a human, primate, a mammal, a tetra pod, a chordate, a deuterostome, an animal, a eukaryote and a living thing. Moreover, we talk of endangered species, and rates of extinction are often measured in number of species going extinct in some unit of time. The feeling that the species ranking is special is not adequately explained as a leftover of Aristotelian ways of thinking. For Aristotle, to say what species something is to give its essence: "essence will only belong to species of a genus, and to nothing else". The same would be true if we added the interbreeding criterion to the mix. It seems, then, that we just have to use different criteria on different occasions. The case for pluralism seems to be a strong one.
