terms

David J. Patterson paddy at EXTRO.UCC.SU.OZ.AU
Fri Jun 17 00:59:57 EST 1994


ROGER

I work with ASHLOCK's definitions, which I think are more sophisticated 
than those normally adopted.  I do so because I know of cases where 
PARAPHYLETIC taxa have to be used.

Do read your copy of Hennig again.  Hennig was rather vague about his 
concepts, and I think that Ashlock did a fine job of clearing up a little 
bit of the uncertainty.  

my usage is:
Monophyly - single origin included in group
Holophyly - monophyly and all descendents
Paraphyly - monophyly and not all descendents
Polyphyly - not single origin

Is this helpful?

David Patterson


On 16 Jun 1994 AROGER at ac.dal.ca wrote:

> >By cladistic point of view, I should have said a cladistic
> >point of view on higher level taxonomy... i.e., that only
> >monophyletic taxa deserve a formal name.  And by monphyletic, I mean
> >those that comprise ALL descendants (to avoid the monophyly holophyly
> >paraphyly business).  The ancestor of all protozoa is also an ancestor
> >of elephants.
> 
> Mark, 
> I disagree with your usage of monophyly.  I have noticed that the 
> Hennigian definition of monophyly is usually insisted upon by 
> those cladistically 
> inclined, eventhough it is not a necessary component of the 
> cladist
>  viewpoint.  As Ashlock pointed out in 1971 (Syst. Zool., 20:63-69),
>  the word monophyly has a root meaning of "tribe of one".  
> A monophyletic
> group is one derived from a single ancestor with the group 
> characteristics.
> The alternative to "mono", is polyphyletic...a tribe derived from at least
> two independant ancestors and whose most recent common ancestor
> was, therefore, not a member of the group.  These two terms form a
>  nicely exhaustive set of alternatives- one, or more than one.  
> And the difference between the two is solely one concerned with 
> the number of common ancestors which give rise to the group.    Hennig
>  invented the term 
> paraphyletic, whose definition depends not on the nature of the 
> ancestors but on
> whether or not all the descendants are included in the group and ranked
> it equally with  mono and polyphyletic.  He redefined monophyletic
> in a more restricted sense as a group comprised of all the descendants of
> a single biological species.   This is confusing because a 
> paraphyletic group  is still a tribe derived from one ancestor 
> and is therefore sort of
>  monophyletic in the earlier but non-Hennigian sense of the word.  
> To rectify the confusion that redefining monophyletic caused,
>  Ashlock
> cleverly preserved the  distinction between mono and polyphyletic
> (which is concerned with the nature  ancestors of the groups) and
>  subdivided monophyletic into holophyletic (containing all descendants of
>  the single most recent ancestor) and paraphyletic
> (not containing all descendants of the most recent ancestor).
> Do you agree with the logic of these definitions?  A cladist could accept
> these terms and still argue that only holophyletic taxa deserve formal
> names.....Clarity and agreement in terms would certainly make the arguments
> about the latter point easier to follow.
> 
> Andrew Roger
> aroger at ac.dal.ca
> Dept. of Biochem.
> Dalhousie University
> Halifax, N.S.    
> 
> 
> 
> 



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