Re: [asa] How big a deal is homology?

Bad choice of words on my part. Continuum has been used by oponants of evolution for what they think darwinism should predict: a seamless continuum without limits among fossil and living species. And of course there are real breaks. The continuum I was referring to was strictly in terms of the methods of using genitic markers to establish family, racial, species, and genus groupings. And I said it "seems" like a continuum to me, to emphasize my uncertainty. Again I'm no geneticist, and I welcome the input of someone who can correct me on that. But it sure seems to me that the same methods are used to establish links among related organisms at all of these taxonomic levels, from individual clans on up.

But I have to stick by my statement that these divisions are arbitrary. Morphological taxonomy does indeed work work well. It's the basis of paleontology. And when I say it is arbitrary I don't mean unimportant. But Linean classification is decidedly arbitrary. With the exception of species and perhaps Kingdom and Phylum, the divisions are completely arbitrary. Certainly there are objective criteria that are used to establish the divisions, but that doesn't make it any less of a judgement call. It's the splitters vs. the lumpers. There is no natural, intrinsic distinction between the family, order or class levels. The position and even the number of divisions is totally dependant on the judgement of human researchers. Within the constraints of the branching hierarchical nature of life, (which is real and compelling evidence for evolution as Terry says), numerous classification systems could have been devised depending on the researcher. But my point in saying that the divisi!
 ons are arbitrary was not to undermine the significance or importance of morphological classification. It was to point out that the divisions do not represent natural limits to evolution. And I ask again how does a micro-evolving population know where to stop to keep from forming a new genus, or family or "kind"? All of the major divisions, fish, amphibian, reptile etc had to begin with a simple speciation. A micro-evolving population just kept going until the morphological separation between the cousin populations could warrent a major taxonomic distinction. The individual organisms just kept reproducing after their own kind and didn't know they were supposed to stop before they crossed the human-conceived line between micro- and macro-evolution.

Brent

---- James Mahaffy <mahaffy@dordt.edu> wrote:

=============
>>> Brent Foster <bdffoster@charter.net> 03/27/07 4:08 PM >>>
Yes that was my point actually. I accept the argument that a common
designer would use common designs. But I was thinking more along the
lines of your examples Terry. We know that DNA sequences can be
inherited. And genetic markers are used to establish identity, family
lines etc. I don't think too many YECs had a problem with the DNA
evidence against O.J. If the same genetic markers are used to establish
phylogenetic relationships between related species, I don't see how one
can except one and not the other. To bring in the Micro- vs.
Macro-evolution contrast, there seems to be a continuum between family
groupings, racial groupings, species groupings, genus groupings etc.

****** me ********

Woa!!!! In at least Zoology and angiosperm taxonomy there seem to be
real breaks (you can argue continuum on some) but the breaks seem to me
who is now teaching Zoology real and must be dealt with. One of the
problems is that a monphylogentic system tends to de-emphasise them as
much or more than a classical system that tended to emphasize groups.
In its very philosophical foundations cladism assumes all (or at least
almost all variation occurs with in a monophyletic line). In case you
wonder I am not TE either or ID for that matter.

The divisions between them are arbitrary.

****** me ********
No they really aren't. Morphological taxonomy worked quite well and
still is fairly important.

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Received on Wed Mar 28 13:46:18 2007