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.
>>>>
