Gary Rosenberg writes that species concepts are "1) taxonomic vs. evolutionary, (2) theoretical vs. operational, (3) contemporaneous vs. clade, (4) reproductive vs. cohesive." So an old-fashioned paleontologist might favor a taxonomic operational contemporaneous cohesive species concept, but a new-fangled molecular biologist might prefer an evolutionary theoretical cladistic reproductive species concept. With all shades of variation in between, and bearing in mind that each of Gary's oppositions are also intergradational. Is that clear, Art? Don't make me come over there! Andrew K. Rindsberg Geological Survey of Alabama Tuscaloosa, Alabama, USA