genetic vs morphological trace of phylogeny

John Grehan jgrehan at SCIENCEBUFF.ORG
Wed Apr 14 11:23:32 CDT 2004

>Curtis wrote:
>This was a long time ago, as such things progress. "Genetically more
>similar" implies a distance measure, and that is no longer done. If
>substitution rates are much higher in one lineage than another, sister
>lineages may be genetically "less similar" than one or the other is to the
>outgroup (just as birds are "less similar" to lizards than crocodiles are).

Perhaps this could be clarified for me as it seems to agree with my view
that genetic similarity is not necessarily a measure of phylogenetic
relationship ["sister lineages may be genetically "less similar" than one
or the other is to the outgroup

>Nothing can be tested with absolute rigor. But our understanding of the
>parameters of DNA evolution is much better, and we can consequently model
>the process better.

I guess this is something that I will need to confirm for myself if there
really has been an advance that changes the underlying assumption from what
Caccone and Powell said.

>I'm no longer exactly responding to John, per se, but addressing those
>points that he brings up that I believe need clarification for others on
>the list. I should mention also (and John to his credit has never accused
>me of this) that I do not discount the similarities among orangs, humans,
>and fossil hominids. I suspect that they will turn out to be
>symplesiomorphies, but I haven't studied the specific issue well enough to
>have an informed position.

I have no problem with that possibility. Unfortunately primate
archeologists and systematists have, for the most part, just ignored the
problem of orangutan evidence. Perhaps in the future.

On a related item posted earlier I have an off list response for general

 >>>I thought the goal of a cladistic analysis using parsimony was to
 >>>identify the tree with the minimum amount of homoplasy. If this is not
 >>>the way you reconstruct your phylogenetic trees I guess all the previous
 >>>discussions have been a waste of time.

Wrong! Parsimony finds the cladogram with the least number of steps so it
can be compared with other 'most parsimonious' cladograms. This is why it
is referred to as an Occcam's razor. It has nothing to do with the least
amount of homoplasy. A cladogram with 100 steps can be less homoplastic than
one with 99 steps.

John Grehan

Dr. John Grehan
Director of Science and Collections
Buffalo Museum of Science
1020 Humboldt Parkway
Buffalo, New York 14211-1293
Voice 716-896-5200 x372
Fax 716-897-6723
jgrehan at

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