[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

pink-haired clade (was "going offlist")



Tim,
I don't really fret much over the rank of most taxa, because I generally follow what others do (taking into account tradition, stability, but new discoveries as well that may warrant occasional changes). Aves has always been a Class and will remain as such even if BCF turns out to be true (and there is a consensus that Aves should be expanded). It has nothing to do with *superiority*, but rather divergence and diversification (and whether paleontologists like it or not, extant groups sometimes get the edge over those that are non-extant, but this is a minor consideration compared to divergence).
However, since you made the comparison, I should also note that the gap between Eubacteria and Metabacteria ("Archaea") is also filling in (just as the theropod-bird gap has filled in). And although I recognize a Phylum Metabacteria (it is indeed different), raising it to a Kingdom (much less Domain) is unwarranted and misleading-----it is as if you raised Aves to Phylum level, and we all agree that this would be unwarranted and unwise. Some constraints are needed to keep classifications balanced. Furthermore, if you then used this "Phylum" Aves as an outgroup to Phylum Chordata, the whole chordate tree would be a ludicrous mess (reptiles evolving into amphibians and then to fish, and a whole lot of other distortions and reversed polarities). That is essentially what is happening in bacteriological systematics. Metabacteria is an ingroup, and using it as an outgroup to Eubacteria is mucking up the whole tree.
Now, I'll start with your pink-haired girl and then generalise from that. We have a mutant girl, the first ever with a recessive pink-hair gene. Pink hair has such survival value that all her descendants soon far outnumber the descendants of her four siblings put together. It becomes convenient to classify all the pink-hairs as a family separate from all her normal-haired relatives.
1 Family Brown-hair
Genus Brown 1
Genus Brown 2
Genus Brown 3
{{Family Pink-hair}}
Genus Brown 4
_a_ Family Pink-hair (very prolific)
Genus Pink 1
Genus Pink 2
Genus Pink 3
Genus Pink 4
Genus Pink 5
You can easily see that the ancestor of the pink-hair clade came from the Brown-hair family. It's not that I regard pink hair as "superior" to brown hair, but it is a convenient way to classify and to reflect a degree of information on diversity and divergence. If the pink-hairs diverged in a whole lot of other characters as well (or if brown-hairs go extinct), I could bump pink-hairs up to Order level (leaving a second place-marker at family level, so we don't lose track of the sister-group information of where the pink-hair ancestor came from). You could easily convert the above into a phylogenetic classification, but unfortunately biological evolution is far more complex than one clear-cut character change (and we are working from a known phylogeny above, which also made it easier).
Phylogenetic taxonomists feel constrained by the Linnean hierarchy because they want to pack way too many of their phylogenetic hypotheses into "formal" nomenclature and classification. Unfortunately phylogenies are unsettled and controversial (and will be for a long time), and therefore these restraints are useful in checking the serious side-effects of purely cladistic classifications. PhyloCode will relax these restraints. I believe stable phylogenetic information should be encoded in a somewhat constrained classification of formal names (maintaining usefulness, and providing the continuity of tradition whenever possible), and all the rest of the information should be encoded informally (coding that can reflect alternative hypotheses and newly acquired knowledge and new hypotheses).
And as much as cladists hate the idea, a small percentage of formal taxa must be paraphyletic (semi-paraphyletic in my system, so the sister group information is not lost). We can quibble how many is optimal, but taking it to zero is far too costly. Mike Keesey has noted that informal paraphyletic groups are allowed in the phylogenetic system, but the side-effects of pure cladism are too high to justify excluding formal paraphyletic groups altogether (and that is where cladists and eclecticists clash most forcefully). The price is too high and only gets higher with time. Cladists either ignore these "costs" or claim they will go back down in time, but I see it as overexuberant optimism and not realistic (and not surprisingly, cladists think the same thing about my approach).
Anyway, as Benton has noted, PhyloCode (and its relative lack of constraint) will lead to chaos in nomenclature (that will probably make today's mess look like a picnic). I understand what PhyloCode hopes to accomplish, but believe those hopes are built on unstable ground. Sorry for breaking my New Year's Resolution concerning PhyloCode, but a lot of us see a nomenclatural disaster in the making.
------Ken Kinman
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com