on defining species

Coyotes, Species Definitions, and Speciation : Mike the Mad Biologist:

One of the reasons I've learned to stay away from debates about "what is a species" is that practical species definitions (i.e., something we can use to classify critters) do a lousy job of describing the process of speciation, while conceptually sound species definitions (ones that describe the speciation process) are usually miserable when you actually try to classify organisms. Why? Because delineating species implies (and requires) sharp biological breaks that might not exist.