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

Re: ...and how ranks don't work was Re: Sauropodz r kewl



Am 19.04.2012 17:20, schrieb evelyn sobielski:

 In the end, the core problem with ranked clades exists for unranked
 clades all the same, it is only a bit less visible: A clade is
 quantitatively superior** to a ranked taxon or an Aristotelian
 ideos, but that only matters so much; it is qualitatively as much a
 fiction as are the others. ALL TAXA ARE UNNATURAL CONSTRUCTS. You
 cannot draw dividing lines through a tree of *unbroken descent* and
 be factually correct. Nature knows only ancestry and progeny,
 mutation and selection. "Clades" don't exist in nature, just as
 "ranked taxa" don't exist.

I disagree. It's not all just in our heads. "Clade" is defined as "an ancestor and all its descendants". Yes, it's not trivial what to consider an ancestor -- with sexually reproducing organisms we have to resort to Mike Keesey's "ancestral sets"/"cladogens" if we aren't content with treating a population as a black box, with multicellular organisms we can look at the phylogeny of individual cells, and then there are cell trees vs. gene trees; hybridogenesis and lateral gene transfer can lead to overlapping but not nested clades; and so on -- but all these complications are _real_. Evolution happens, phylogeny exists, we can represent it as a largely tree-shaped network, define parts of it and name them.

 ** Though not necessarily. Imagine a branch-delimited or
 node-delimited clade, for which we have a complete set of specimens
 from the node and immediately around it. They need to be stored
 somewhere, in a labeled box arranged with lots of other such boxes in
 a cabinet or similar. This practical problem cannot be solved in a
 workable way if taxa are strictly made to correspond to clades [...]

When you can't have nested cabinets (...well, usually you can't), organize your collection the way Michel Laurin organizes his reprint collection. He has a lot of folders that are meant to be nested. Of course they aren't, they're in a linear sequence on shelves, but they're meant to be nested and labeled accordingly. Every paper gets put into the most highly nested appropriate folder: articles about crown-group salamanders go into the Urodela folder, articles about salamanders in general or specifically about stem-salamanders go into the Caudata folder. Many folders have paraphyletic contents like this, but they're labeled with the name of the smallest clade that contains it.

If such a system is not clear enough because you can't run up and down the collection room to see which subtaxa have their own shelf, mention on the labels which subtaxa have their own shelf.

IIRC, that's how the herbarium at Yale is organized.