Hi Jim, I appreciate your enthusiasm about the fascinating topic and your apparent longing for a clear and fair discussion: From my perspective as a morphologist I fully agree with the first half of your sentence: "the DNA sequence of the organism IS the organism ", but I disagree with your conclusion in the second half of your sentence: "so the DNA sequence perforce defines the species." Only the last word "species" is wrong in my opinion. It might be replaced by the "individual organism". Proposal of a proof by falsification: Every individual human has its own DNA sequence, but every individual human is certainly not a species of its own. Here I took your word "DNA sequence " literally, whereas you had in mind something like the "essential DNA sequence " of a species. How works your recipe to eliminate all the individual DNA sequence differences in order to distil the DNA sequence of a species? Do you understand my and your problem. From your perspective as a biochemist, "Geography and morphology are just approximations of the species." From my perspective as a morphologist, the DNA sequence is just one morphologic character (to a certain extent the most powerful one, if well handled) to find out, how to circumscribe a species. There are different levels of morphologic characters: In botany we start with the growth form and the variations of the three basal organs, at a lower level we have anatomy. These levels can be called alpha-taxonomy. One level further down in size cytotaxonomy was the most modern taxonomy for some decades. Again further down in size chemotaxonomy followed. Since about two decades molecular taxonomy is the most modern branch of taxonomy, but good morphology always remains a healthy basis. Cheers Dietrich Am 31.10.2012 12:37, schrieb J.E. Shields: > This is indeed a fascinating topic. From my perspective as a biochemist, > the DNA sequence of the organism IS the organism, so the DNA sequence > perforce defines the species. Geography and morphology are just > approximations of the species. > > I'm not sure how deeply this notion has permeated the rest of biology from > the molecular biological side, but it is inevitably the direction things > are going to go. Until DNA sequencing becomes routine (i.e., a block box) > and really cheap, we are stuck with morphology and to a secondary extent, > geography. > > Operationally, the weakness in the biological species concept is that we > can rarely if ever actually define the "breeding population." It is not > really definable (in terms of "do this then this and you define the > breeding population" using any doable steps) so it is not really a > scientific concept. > > Jim Shields > > At 08:39 PM 10/30/2012 -0700, Nhu wrote: >> This is such a juicy subject that I have to join (just for a little). >> >> It's always good remember that no one knows what a species truly is. >> Taxonomy and the latest and fanciest science could not yet tell us that >> yet. However, taxonomy has been pretty good at *recognizing* species. What >> we humans recognize as species does not make something a species, but it >> has its practical purposes. >> ..... > ************************************************* > Jim Shields USDA Zone 5 > P.O. Box 92 WWW: http://www.shieldsgardens.com/ > Westfield, Indiana 46074, USA > Lat. 40° 02.8' N, Long. 086° 06.6' W > > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/