[Taxacom] Knocking Hennig off his pedestal

Patrick Alexander paalexan at polyploid.net
Sat Jan 25 23:51:08 CST 2014


Or, phrased in a manner that seems more straightforward to me:

Polyphyletic groups are based on homoplastic character states. Both 
monophyletic and paraphyletic groups are based homologous character 
states. For monophyletic groups the homologous character states are 
apomorphic, while for paraphyletic groups they are plesiomorphic.

However, this is just shoehorning phylogenetic terms into typology. It 
assumes that you start with an ahistorical, similarity-based 
classification and then examine how that classification maps onto 
descent. A grouping of species is, on its own, only monophyletic or not. 
Paraphyly and polyphyly are not characteristics of groups of species, 
they are characteristics of a typological classification of those 
species. They are only distinguishable if you accept a priori that 
typology is the appropriate approach to defining groups of 
species--which, of course, is diametrically opposed to the goals and 
concepts of phylogenetic classification, which defines groups of species 
by descent. From the viewpoint of phylogenetic classification, they are 
equally bad because they are indistinguishable.

Patrick

On 1/25/14 9:24 PM, Stephen Thorpe wrote:
> Paraphyletic groups are based on plesiomorphies. They exclude decendants whose plesiomorphies have evolved into apomorphies.
> Polyphyletic and monophyletic groups are based on apomorphies. In the former case, the apomorphies are independently evolved more than once, so the group fails to be monophyletic by excluding some decendants of the most recent common ancestor of all the apomorphic members (i.e. the ones who have retained the plesiomorphic states).
>   
> Stephen
>
>
> ________________________________
> From: John Grehan<calabar.john at gmail.com>
> To: Ken Kinman<kinman at hotmail.com>
> Cc: Stephen Thorpe<stephen_thorpe at yahoo.co.nz>; Fred Schueler<bckcdb at istar.ca>; "taxacom at mailman.nhm.ku.edu"<taxacom at mailman.nhm.ku.edu>
> Sent: Sunday, 26 January 2014 5:06 PM
> Subject: Re: [Taxacom] Knocking Hennig off his pedestal (was: categorical systematics
>
>
>
> I'm sure that there are some cladistic experts who will be able to comment better than I, but in my limited understanding, paraphyletic groups are groups that fail to include all descendants of a common ancestor (as defined by some uniquely common character state/s). In that sense, both groups (for black and for white circles) in Fig a seem to me to be paraphyletic as both fail to include all descendant taxa. But probably I have overlooked something obvious.
>
> John Grehan
>
>
>
> On Sat, Jan 25, 2014 at 8:27 PM, Ken Kinman<kinman at hotmail.com>  wrote:
>
> Dear All,
>>        I was just looking at a recent discussion by Thomas Cavalier-Smith criticizing Hennig's (1974) argument trying to convince us that paraphyletic and polyphyletic taxa are cladistically equally bad (something that strict cladists have repeated ad nauseum for decades).  Especially note the figure on the right and the discussion below it.
>> http://openi.nlm.nih.gov/detailedresult.php?img=2842702_rstb20090161f02&req=4
>> -------------------------------------------------------------------------------------------------------------
>>
>>> From: kinman at hotmail.com
>>> To: stephen_thorpe at yahoo.co.nz; bckcdb at istar.ca; taxacom at mailman.nhm.ku.edu
>>> Date: Sat, 25 Jan 2014 03:21:02 +0000
>>> Subject: [Taxacom] Knocking Hennig off his pedestal (was: categorical systematics
>>>
>>>
>>> Hi Stephen,
>>>          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.
>>>                        ----------------Ken Kinman
>>>
>>>
>>>
>>>
>>> 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.
>>>
>>> Stephen
>>>
>>>
>>>
>>>
>>> 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. ___________
>>
>>
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