> This research has consistently shown that the phyla have developed
> in the top-down direction, from general to specific taxonomic forms, from
> Phyla, to Classes, to Orders, etc. This is just the opposite direction from
> what Darwin predicted.
We've been through this before! As I have said repeatedly, the "top down"
pattern is the consequence of retrospective taxonomy applied to a branching
tree of life. Below is a paragraph from my recent article in Perspectives
"The Precambrian to Cambrian fossil record and transitional forms."
>Battson (1994) emphasizes the pattern of appearance of higher taxa in
>which phylum-level diversity reaches its peak in the fossil record before
>class-level diversity, and class-level diversity before that of orders,
>etc. Battson and other critics of macroevolution interpret this apparent
>"top-down" pattern as contrary to expectations from evolutionary theory.
>However, this pattern is generated by the way in which species are
>assigned to higher taxa. When a hierarchical classification is applied
>retrospectively to a diversifying evolutionary tree, a "top-down" pattern
>will of necessity result. Consider, for example, species belonging to a
>single evolving lineage that is given genus-level status. This genus is
>then grouped with other closely related lineages into a family. The
>common ancestors of these genera are by definition included within that
>family. Those ancestors must logically be older than any of the other
>species within the family. Thus the family level taxon would appear in
>the fossil record before most of the genera and species included within
>it. The "top-down" pattern of taxa appearance is therefore entirely
>consistent with a branching tree of life.
I also discuss this in my web article on the ASA webpage "Taxonomy,
Transitional Forms, and the Fossil Record." If people are interested in
this please read both the Perspectives and web articles.
I will be away from e-mail until January 9, so I will be unable to respond
to any questions directed to me until then.
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506