Essential Reading on the Species Concept

Ted Floyd has put up an absorbing (and challenging) article on the limits of the species concept at the ABA Blog.  This is essential reading, especially for birders interested in evolution, regional variation, and identification to sub-species.  Among many other things, Floyd discusses Darwin at length, talks about Arnold Shoenberg and atonality, and defends David Sibley's decision to use regional names for sub-species in The Sibley Guide to Birds.  Make sure to read the comments!