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.
Paul Nelson replies:
>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.
Then again, one could take common ancestry to mean that
organisms share many parts from an earlier pool of components
(possibly not shared by all progenitors, but largely in common).
One could achieve such a state even if the rate of horizontal
transfer was low, relative to linear descent.
>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:
>
>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).
Paul, would you care to recount Doolittle's discussion in this
area and perhaps extrapolate to how it may pertain to things
such as mitochondrial phylogeny, deuterosomes or vertebrates?
[end of excerpt]
[quote removed..TPI]
>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.
Which levels for instance? Eukaryotes? Plastid phylogeny? Higher
primates?
In actuality, what is being discussed by Doolittle et al. is whether
large bouts of horizontal transfer preceded the split between
the eubacteria, archeabacteria and eukaryotes, which would obscure
the past evolutionary trajectories of these groups. There are certainly
instances of horizontal transfer after the split, so there is no
reason to suspect that genomes were necessarily as fixed as many are
today. I personally would not be surprised if this was the case and
I would like to note further that most of proposed episodes of
horizontal transfers discussed by Doolittle are confined to single-celled
organisms.
But based on current evidence, can one truely question monophyly
at "various levels" much higher than that delimited by, say, higher
eukaryotes? I realize Paul, that you question human/ape monophyly,
but do you suppose that Ford's comments could be used to reasonably cast
doubt on many vertebrate phylogenies? Does another Fellow at your
institute, Mike Behe, question common descent at such levels?
BTW, Paul - Here's a question I've always wondered about, but for
which 've never seen a clear answer: What's Phil Johnson's position
on common descent? Largely in agreement, partially in agreement,
not in agreement, strongly in disagreement? I would personally
love to see an answer which is not obfuscated by political sophistry.
I mean, does this guy really have a scientific position on anything
that he's willing to discuss in a forthright manner?
Regards,
Tim Ikeda
tikeda@sprintmail.hormel.com (despam address before use)
This archive was generated by hypermail 2b29 : Mon Jul 24 2000 - 19:55:51 EDT