[Taxacom] "Natural" groups

[Kenneth Kinman]

Hi Barry,
         The idea of monophyly in the broad sense
(including both holophyly and paraphyly) being the basis of natural
classifications and natural taxa goes all the way back to Darwin.  He
clearly argues that classifications must be "genealogical in order to be
natural, but that the amount of difference in the several branches or
groups, though allied in the same degree in blood, to their common
progenitor, may differ greatly, being due to the different degrees of
modification which they have undergone, and this is expressed by the
forms being ranked under different genera, families, sections or
orders."  Of course, he doesn't use the terms monophyly, holophyly, or
paraphyly (which were coined later), but his meaning seems clear.            
        In the case of Reptilia, although crocodylians
and birds have common reptilian progenitors (the first amniote, the
first diapsid, and many others along that stem lineage, "they differ
greatly" due to different degrees of modification, and this can be
expressed by these "forms being ranked under different" ranks. In that
case, during the 20th Century, Crocodylia was ranked as an Order and
Aves as a Class.       
        Ernst Mayr strongly endorsed this Darwinian concept (of
strikingly different degrees of modification being reflected at
different ranks) during his career which spanned much of the 20th
Century (as did a majority of taxonomists). It wasn't until Hennig came
along that such paraphyly was branded as being unnatural.  Hennig
created a great tool for phylogenetic analysis, but branding all
paraphyly as unnatural was overkill (in response to sloppy and excessive
paraphyly).  Reactionary swinging of a pendulum almost never has good
results, whether you are a strict cladist reacting to excessive
paraphyly, or Communists reacting to bad czars, and even the French
cutting off too many heads because Marie Antoinette was so spoiled and
ignorant.  Anyway, Darwin was far ahead of his time, while Hennig made
mistakes in spite of another century of information available to him.
There's no comparison, and strict cladists who put Hennig on a pedestal,
while bad-mouthing Darwin (and his 20th Century supporters) are making a
big mistake.  Too much Hennigianism and too little Darwinism does not
create an optimal mix.                    
               ----------Ken Kinman               

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Barry Roth wrote:
     Use of the term "natural group" goes back a long way, to before the
art or science of estimating phylogenetic relationships was very far
advanced. It would be interesting to see some definitions from, say, the
1920s. Has that term always implied monophyletic (in the broad sense,
paraphyly having become a concern later) groups?