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Date: Thu, 17 May 2001 13:26:28 -0400
From: David Baum <dbaum@oeb.harvard.edu>
To: PhyloCode@ouvaxa.cats.ohiou.edu
Subject: Stepping back
Hi All, I have been rather dismayed by the discussion over the last month because it can only have served to confuse people. In an attempt to bring the discussion back into focus I have jotted down some of the reasons that I think rank-free nomenclature is such a good idea and why it is worth putting some thought into how best to arrive at that aim. I have done this fairly quickly so the points listed below reflect my internal reasoning rather than the formal arguments one might present if the aim was to convince a skeptic/cynic. But maybe it is better to articulate why I am committed to this new brand of nomeclature rather than trying to convince other people to get on board? Anyway here it is. 1) The capacity to formally name any taxon that a systematist sees as worthy of naming and to regulate subsequent usage of that name is a necessity to avoid nomenclatural chaos. [i.e., we cannot depend on informal names and conventions] 2) The traditional systems depend heavily on ranks - but we all know that ranks (as opposed to clades that have been assigned historically to a particular rank!) are not real. Unless you will claim that there is something inherent in the distinction between, say, a family and an order, then it is ridiculous to build a system around ranks. 3) Getting rid of ranks is not possible with the current system because a rank defines the intension of a name. For example, Malvaceae <bold>IS</bold> that family containing Malva sylvestris L. 4) To get rid of ranks one needs new ways to attach names to taxa via concrete types (or specifiers). The phylocode allows for three (can we think of more). 1) Node-based: lists two or more types and refers to the smallest clade including all these internal types. 2) Stem-based: Refer to one internal type (in my view only one internal types should be listed - but the draft code allows multiple internal types) and one or more external types and refers to the largest clade including the internal types but none of the external types. 3) Apomorphy-based (personally I wish this mechanism were disallowed): Refers to one internal type plus an apomorphy manifested by that type and reference to the smallest clade composed of individuals manifesting that apomorphy. 5) While the PhyloCode elegantly gets rid of ranks it represents a big change from traditional system because the correct application of names depends upon phylogenetic knowledge (rather than opinions about rank). If people define names based on an incorrect tree then the content of those taxa could change later. This is a inconvenience but not, to my mind a big one. If people are responsible in only naming well-supported clades then it should not occur too often. And even when such a shift does happen, biologists will quickly learn. 6) I like the rank-free system because provided two biologists agree on a tree then the correct name of each clade is unambiguous. So any arguments about nomenclature are about phylogeny - and I view phylogeny as a useful thing for biologists to be studying. In contrast under the traditional code nomenclatural arguments rarely turn on issues of biology. 7) As a new code, names can be registered from the outset avoiding the problem of overlooked names being discovered that have priority over familiar names. 8) The PhyloCode does not need new names whenever familiar names fit with clades. For example, Angiospermae turns out to correspond to a real clade so that name can be retained but given a rigorous definition. 9) Since names can exist simultaneously as both ranked names governed by the traditional codes and unranked clades governed by the PhyloCode there needs to be an convention for distinguishing the two. [We have proposed a forward slash as a clade mark, thus distinguishing family Malvaceae from clade /Malvaceae] 10) No hybrid system is possible because ranks are intrinsic to the traditional codes and incompatible with the PhyloCode. Thus, any transition that might occur (as I hope it will) will involve a period of coexistence. 11) The phylocode must deal with species. There are several viable ways in which it could but, due to differences of opinion among the code's developers, no one approach has been approved. 12) There are other subtle issue within the PhyloCode that warrant discussion but those can only be got into once there is agreement on the preceeding points. I hope that is helpful. David David Baum Dept. Organismic and Evolutionary Biology Harvard University Herbaria 22 Divinity Avenue Cambridge MA 02138 Tel: (617)496-6744, -8766 Fax: (617)495-9484 dbaum@oeb.harvard.edu http://www.herbaria.harvard.edu/~dbaum After July 15: Dept. Botany, University of Wisconsin 430 Lincoln Drive, Madison WI 53706 dbaum@facstaff.wsic.edu