>The top-down, hierarchical pattern, however, is not forced upon the data. It
>is not generated by the classification process as Miller claims. The pattern
>is rather, a true and valid reflection of the hierarchical way that nature is
>organized.
Bob follows this by redescribing the pattern. The pattern is not in
dispute - the reason for its existence is. The "top down" pattern of taxa
appearance _is_ generated by retropectively grouping taxa hierarchically
from a diversifying tree of life. Test this for yourself, draw an upward
branching tree (use Darwin's own diagram). Now begin at the top by grouping
branches until you reach the bottom. You will find that the more inclusive
groups appear first. A higher taxonomic group begins of necessity with a
single species, which then diversifies over time. The failure of the
present classification system to capture this was one of the motivations
for the development of the cladistic classification system now in favor by
many biologists and paleontologists.
A category, any category, is not objective fact but a human construction
designed to capture certain (but not all) aspects of reality. As
classification and evolutionary theory changes the taxonomic assignments of
fossils keep changing.
> Moreover, his claim
>that the "origin of higher taxa [arose] through evolutionary processes at the
>population and species level" is challenged by the authors' {Erwin,
>Valentine and Sepkoski) claim that "The
>higher taxa do not seem to have diverged through an accumulation of lower
>taxa."
My statement is supported by the very authors that Bob cites. Valentine
("The macroevolution of phyla." In, Origin and Early Evolution of the
Metazoa, 1992, p. 525-553) states, "A phylum has had to originate as a
founding species by definition, and thus via microevolutionary processes.
The microevolutionary questions concern how and why such a speciation
occurred: what genetic, ecologic, or other features in the poplation
bioloby of the lineage conspired to produce the new species." I know of no
evolutionary biologist who would dispute this.
Keith
Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506
kbmill@ksu.ksu.edu
http://www.ksu.edu/~kbmill/