[Taxacom] Knocking Hennig off his pedestal (was: categorical systematics
kinman at hotmail.com
Fri Jan 24 21:21:02 CST 2014
Thanks. I would agree with that, but not sure about "particularly for extant taxa (a time slice of the tree)." Extant taxa at higher levels (especially Family and above) are quite variable in how much their continuum can be sampled and classified.
For instance, Diptera (which Hennig studied) went through the end-Cretaceous extinction relatively unscathed for family level taxa (as long as they had members who could feast on lots of dead plants and animals). So I was not surprised that even my own classification of Diptera turned out to be very cladistic (very little paraphyly needed).
Most vertebrate groups (especially on land) suffered far more extinction than taxa like Diptera (or Eubacteria or even many fungi). Not a good time to be at or near the top of the food chain. "A time slice of the tree" goes back pretty far for extant families and orders of bacteria in particular. And that's yet another reason why geological dates of divergence are so problematic across the board.
I guess Hennig was too fixated on Diptera to realize how inappropriate strict cladism was for many other taxa. You can get by with little or no paraphyly classifying Diptera. But it causes problems in other taxa (somewhat in higher plants, and even more so in tetrapod vertebrates).
Thus differential extinction rates in different higher taxa means that paraphyly tends to be more useful in those taxa that are extinction sensitive (often because they are higher in the food chain, or can't go dormant like buried frogs or plant seeds, or just too specialized in some other way). Too much variability for geological divergence times to be of much use in most higher taxa (even IF such divergence times were more accurate).
Seems like the time has finally come for the hero worship of Hennig to end, knock him down to at least a lower pedestal, and realistically look at what his overly strict cladism has cost us for several decades. His criticism of excessive paraphyly certainly bore much fruit, but when he swung the pendulum too far the other way (no paraphyly allowed at all), he just set the stage for a whole different set of problems to develop over time.
When it gets to the point where birds are buried within a long indented series of extinct dinosaur clades (some of which are phylogenetically controversial and unstable), it's time for a new paraphyletic break somewhere between dinosaurs and birds to be recognized. It's not quite the nice continuum it is made out to be, and the phylogeny itself periodically changes with unanticipated new fossil discoveries. Not surprising given that so many transitional forms are pretty scrappy bits and pieces of bone.
When it gets to that point, it is not surprising that many strict cladists threw up their hands and said we must abandon categories. But if you abuse any such useful tool, it is bound to break from such abuse. Early on (in the late 1970s), I choose a different approach, limiting both the number of Linnaean categories and the number of paraphyletic taxa at the same time. Many intermediate Linnaean categories (and their taxa) were replaced by a coding system (as one can see in my Protista classification). A classification is much more stable with fewer formal intermediate categories, and you can readily reflect new phylogenies by modifying the coding and/or the placement of some taxa. This approach has been particularly successful with the Protista, whose phylogeny has been very unstable for the past 20-25 years. But I am now tired of arguing about this, so I am off to bed.
Date: Fri, 24 Jan 2014 15:18:44 -0800
From: stephen_thorpe at yahoo.co.nz
Subject: Re: [Taxacom] categorical systematics
To: kinman at hotmail.com; bckcdb at istar.ca; taxacom at mailman.nhm.ku.edu
Yes, just because the totality of evolution is a continuum (which may not actually be quite true?), doesn't mean that discrete categories aren't appropriate for classification, particularly for extant taxa (a time slice of the tree), and the fossil record is so fragmentary that we will never see much of the continuum anyway.
From: Ken Kinman <kinman at hotmail.com>
To: Fred Schueler <bckcdb at istar.ca>; "taxacom at mailman.nhm.ku.edu" <taxacom at mailman.nhm.ku.edu>
Sent: Saturday, 25 January 2014 12:00 PM
Subject: Re: [Taxacom] categorical systematics
Hi Fred, But we never be able to sample but a small percentage of that continuum. Extinction has already chopped the tree of life into bits and pieces, and we can only sample a small percentage of those bits and pieces that have survived. So in my opinion we are actually sorting and categorizing what bits and pieces we can collect, and thus putting them into groups (which is the opposite of taking a whole and chopping it up). Linnaean categories have served us well in this process over many generations, and in my opinion so have many paraphyletic taxa (and I thank David Campbell for his comments on that). -----------------Ken
------------------------------------------------------------------------------------------------------------Fred Schueler wrote:Evolved taxa are naturally categorical classifications, but Linnaean categories are a partitioning of a continuum into segments, and I suppose I'm just biased against this practice.In our autobiographical whinge - http://pinicola.ca/transition.ca-we write "Fred also realized, during the composition of his thesis, that in every case where he'd classified a phenomenon into categories, the situation was better explained as an ordination or regression – a response to continuous variables, rather than a chopping-into-parts. _______________________________________________Taxacom Mailing ListTaxacom at mailman.nhm.ku.eduhttp://mailman.nhm.ku.edu/mailman/listinfo/taxacomThe Taxacom Archive back to 1992 may be searched with either of these methods:(1) by visiting http://taxacom.markmail.org/(2) a Google search specified as: site:mailman.nhm.ku.edu/pipermail/taxacom your search terms hereCelebrating 26 years of Taxacom in 2013.
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