Doug Hayworth wrote:
> If one does NOT accept common ancestry
> (or, speaking in terms of forward time,
> speciation), then there is nothing left
> worth discussing with him/her relating
> to evolution. Such a person has turned
> him/herself off to the validity of my
> entire scientific discipline at such a
> fundamental level that we are without
> any common ground.
I take it that by "common ancestry," Doug means the
theory of the monophyly (or shared common ancestry)
of life on Earth, where any extinct or extant organism
shares at least one organismal ancestor in common
with any other organism, namely, the Last Common
Ancestor, often abbreviated LCA or LUCA.
If so, then one can certainly reject or doubt this theory
and remain fully within the discipline of evolutionary
biology. I reproduce here a portion of a post I sent
recently to another list:
[excerpt begins]
The molecular evolutionist W. Ford Doolittle
of Dalhousie University continues to cast doubt
on the historical existence of the LUCA -- i.e.,
the Last Universal Common Ancestor, the Urparent
at the base of Darwin's Tree of Life. In his most
recent article, "The nature of the universal ancestor
and the evolution of the proteome," _Current Opinion
in Structural Biology_ 10 (2000):355-358, Doolittle
argues that if the LUCA did exist, it was a cell
unlike any we know, packed with a great range of
biochemistries now distributed separately among
various groups of prokaryotes:
...there is a very large pool of genes shared among
contemporary bacteria and archaea that are never all
(or even mostly) found in any one bacterial or archaeal
genome. If we follow the simple rule of parsimony
without LGT [lateral gene transfer], we wind up with a
*totipotent ancestor*, with a proteome [protein profile]
considerably more complex than that of any modern
prokaryote. This cell must have been capable of almost
the full range of the autotrophic and heterotrophic,
anaerobic and aerobic biochemistries separately found
among all the diverse prokaryotes in today's microbiota!
(p. 356, emphasis in original)
Under the heading, "Is a single universal ancestral cell or
species really necessary?" Doolittle answers No. And
note his choice of an illustrative parallel case:
Thus, there is no more reason to imagine only a single
first kind of cell as the progenitor of all contemporary
life than there is to imagine only Adam and Eve as
progenitors of the human species. (p. 356)
In the concluding section of his paper, Doolittle grapples
with the consequences of his view for the standard definition
of homology (i.e., similarity due to common ancestry).
[end of excerpt]
See also UCLA biologist Malcolm Gordon's article, "The
Concept of Monophyly: A Speculative Essay," _Biology and
Philosophy_ 14 (1999):331-348. Gordon argues that the
concept of monophyly [common ancestry] "at the macro-
scales of evolutionary differentiation appears to be
severely limited....the phenomenon of a monophyletic
origin for the universal tree of life probably did not
occur" (p. 343).
These are minority viewpoints, of course. Most evolutionary
biologists accept the monophyly of life as a background theory
in their day-to-day research.
But that's not the point at issue. It is increasingly possible
to cast doubt on monophyly at various levels in the taxonomic
hierarchy without stepping outside the arena of reasonable
scientific discourse.
Paul Nelson
Senior Fellow
The Discovery Institute
www.discovery.org/crsc
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