tag:blogger.com,1999:blog-3342041114052632712.post3489408655949309513..comments2024-01-20T16:39:42.179+11:00Comments on PhyloBotanist: The hegemony (or not) of cladismAlex SLhttp://www.blogger.com/profile/00801894164903608204noreply@blogger.comBlogger1125tag:blogger.com,1999:blog-3342041114052632712.post-38109997166532130812015-12-21T09:41:09.443+11:002015-12-21T09:41:09.443+11:00“Finally, there is the question of rank-free class... “Finally, there is the question of rank-free classification. Of course, not every cladist is a PhyloCoder, but it does seem to me that one of the insights that follow logically from phylogenetic systematics is that ranks above the species level are ultimately arbitrary and meaningless. Diversity is organised in nested clades, but you cannot meaningfully compare a genus of beetles and a genus of algae; there is no genus-ness in nature.”<br /><br />It’s an important insight. That it is not universally understood goes a long way toward explaining why there is still opposition to phylogenetic systematics. While no one would compare a genus of beetles and a genus of algae, there are still taxonomists (cladists among them) who think that within a narrower community of researchers (i.e. entomologists), ranking a group of species as a genus rather than a family is a convention that implies (or should imply) something about their degree of phenetic similarity.<br /><br /><i>There is an equivalence of taxa assigned the same categorical level within broad groupings. So, for example, dogs (Canidae) are separate from cats (Felidae), and all “families” within the order Carnivora share common characteristics: a similar amount of morphological disparity, genetic divergence, and time since origin. The species in “families” of Carnivora, assessed in terms of any genetic or morphological measure, plot in hyperspace as equivalent-sized clouds of points separated from each other by equivalent distances. The decision by generations of Linnaean taxonomists to name these clusters all as families was not therefore random. The decision reflects a reality in the way taxa plot on trees, as well as evolutionary conservativeness and ecological adaptations of closely related species. It is no wonder then that generations of biologists have accepted the practical equivalence of families of carnivores, and perhaps of all mammals. It might not be unreasonable to suggest that the marsupial Family Petauridae has broad equivalence to the placental Family Canidae. But few, if any, have ever claimed that a family of fishes, bivalves or angiosperms is equivalent in any meaningful way to a family of mammals.</i><br />Acta Palaeontol. Pol. 52 (3): 651–655, 2007<br /><br />It’s surprising to hear this from Michael J. Benton, a paleontologist and a cladist, because as you’ve pointed out, the morphological disparity between cats and dogs is an illusion brought about by extinction and an incomplete fossil record. When supraspecific taxonomic ranks are applied asynchronously, their phenetic “information content” can at best be a good representation of a sampling artifact.<br /><br />Once I got out of the habit of attaching significance to taxonomic rank, it became clear that phylogenetic systematics can be just as practical and even more flexible than “evolutionary” systematics, simply by naming or emphasizing only those clades are most useful for a given purpose (distinctive apomorphies, geographic range, evolutionary novelties, whatever).Dannoreply@blogger.com