Lucy in Newsweek

[John Grehan]

At 07:44 AM 4/2/04 -0800, Curtis Clark wrote:
>At 06:01 2004-04-02, John Grehan wrote:
>>It is my opinion that the DNA data
>>has more potential for being misleading as it seems to be phenetic - for
>>all that it may be run through clustering algorithms used by cladists.
>
>"Phenetic" is a type of analysis, not a type of data. And you have yet to
>present evidence that the "clustering algotithms" used for morphological
>analysis are inappropriate for DNA sequences.

Don't think I ever said they were inappropriate - just that they don't make
the characters cladistic.


>>It's only numbingly difficult if one takes that to be the case. The
>>alternative is to consider that overall similarity of DNA sequences really
>>have little to do with the phylogenetic sequence.
>
>Perhaps "overall similarity" is not the best measure, but I can't believe
>that you are suggesting that evolutionary history leaves traces in the
>morphology, but not the genome.

Nope - never said that. Just as there may be morphological similarities
that don't track phylogenetic sequences, there may be 'genomic'
similarities that also don't track phylogeny. In the orangutan case I am
inclined to the view that the preponderance of human-orangutan
synapomorphies is so great (and the subjective role of these characters are
sometimes so prominent) that I view the DNA evidence to be more
questionable. Others feel differently.


>>I have proposed that the
>>only sequences that are relevant to such a sequence are those involved with
>>the morphological synapomorphies (and if I understand my genetics well
>>enough, the DNA representation of each synapomorphy may be scattered in
>>different locations on DNA strands as they are brought together through RNA).
>
>So what you are saying is that you choose the evidence that supports your
>case, and then only consider the genes that putatively code for it? Nice.

Not necessarily. If there was a preponderance of human-chimp morphological
synapomorphies the argument would still hold - although I do not believe
genes 'code' 'for' anything. Too preformationist for my liking.


>>So far I do not see the DNA being verified as synapomorphies at all.
>
>The procedure is the same as for morphology: root with an appropriate
>outgroup. Since you are familiar with the literature, you should be able to
>ascertain whether this has happened.

Rooting phenetic characters seems to me to be problematic. Often enough the
orangutan is CHOSEN to root the tree, and thus it is already left out of
the picture (as in that recent example I posted).

John Grehan



>--
>Curtis Clark                  http://www.csupomona.edu/~jcclark/
>Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
>Professor, Biological Sciences                   +1 909 869 4062