joe@ENTROPY.MS.WASHINGTON.EDU (Joe Felsenstein) (10/09/88)
In response to Dan Davison's remarks on the Roger Lewin articles on
the Sarich-Sibley ruckus. These are good articles which fairly
well air the issues in this controversy. There are a number of
unrelated issues:
(1) Whether Sibley and Ahlquist's data is marred by "corrections"
which were (a) not explained and (b) perhaps not justified. This
remains to be seen when they explain the corrections and release the
original data. Certainly they owe everyone an explanation.
(2) Whether DNA hybridization data on relationships is fatally flawed
owing to presence of some repeated sequences. I am not convinced of this
(indeed, it is not an issue raised by Sarich and Marks except in their
advocacy of delta-mode rather than delta-T50H or delta-Tm as a measure
of the extent of hybridization. Presumably they feel that this
different measure would avoid any such problem. Here I would ask
Dan Davison for some details on why he thinks "fractured, highly
repetitive elements" would cause trouble. If there are enough different
repeated sequences involved, then we should still be able to use them
to measure average divergence of sequences.
(3) Whether there is a fatal flaw in the use of any data like
DNA hybridization which must be analyzed as distances rather than
by reference to individual sites. Sarich is NOT raising this issue
-- he is a long-term DEFENDER of use of distance measures and methods.
But without knowing Marks, I get the impression that he comes from
the "phylogenetic systematics" tradition which considers that there
is something fatally wrong with distances. In any case, although the
issue is not being raised by Sarich and Marks, it is clear that many
phylogenetic systematists consider this to be the issue and that any
discomfiture of Sibley reinforces this position. Even if everything
Sarich and Marks say is accepted I don't see that this point follows
at all. I have argued (in papers controversying with Farris) that
there is not a fatal flaw in distance methods.
(4) Whether Sibley is a fast-talking super-salesman who overstates his
case. Here there is no controversy at all. The fact that he is has
caused lots of people, particularly avian systematists, to be rooting
against him. I think it would be sad if this led to acceptance of
objections (2) and (3) (and too-easy acceptance of (1) before the
evidence is in). There are similar objections involving style of
communication that could be raised about Sarich.
It is sad and counterproductive in science when issues become confused.
This seems to be happening in this case, and the Lewin articles will
be useful to the extent that they allow people to separate some of the
issues.
Dan -- care to expand on your remarks?
---
Joe Felsenstein, Dept. of Genetics SK-50, Univ. of Washington, Seattle WA 98195
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