Re: Oldest Plant species?

Arthur V. Chadwick (chadwicka@swac.edu)
Mon, 06 Oct 1997 15:25:08 -0700

At 03:25 PM 10/6/97 -0400, David wrote:
> There's no particular difficulty for evolutionary theory in the
>long persistance of certain kinds. "If it ain't broke, don't fix it"
>applies to evolution as well as machines. Anything that works well is
>likely to have stabilizing selection (i.e., anything that mutates too far
>from the norm will beat a disadvantage and gets selected against). Such
>renaming can reflect evolutionary preconceptions or varying views of what
>should constitute a genus (e.g., splitter versus lumper or strict
>cladistics versus more traditional approach), as well as the discovery of
>actual differences. Convergence may be argued for if there are no known
>similar forms between the older and modern examples; however, such gaps can
>also represent a lack of known fossils rather than original absence.

True, stabilizing selection is a possible explanation for apparent
persistence in the fossil record, but it does little to explain how these
forms got to be so perfect that when they first appeared as a class, they
needed no modification in the subsequent "50 million years". There is no
sense in speaking about convergence when for example the Acer I cited is
known from leaves, flowers and fruit. The renaming of plant form genera
has been in general a rather undisguised effort to dilute the effect of
having no evolution subsequent to first appearance. Nearly all angiosperm
families are known by upper Cretaceous and this is mostly based on leaf
morphologies and some pollen, both of which are characteristically modern
in form and clearly assignable to modern taxa at the genus level.
Art
http://chadwicka.swau.edu