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basic behavioral systematics (once again!)

Joe Felsenstein joe at GENETICS.WASHINGTON.EDU
Sat Apr 27 11:08:55 EST 1991


In response to Jim Danoff-Burg's posting in "bionews" (let's move this to the
more appropriate groups "population-biology" and "molecular-evolution" rather
than "bionews"):

> That is: traditionally, systematicians have looked for those
> characters that they view as being completely (or nearly so) from the
> force of natural selection.

Did you mean "completely free from the force of natural selection" or
"completely resulting from the force of natural selection"?  That was
the wrong word to forget to type in the sentence!

My impression is that many systematists tried for the former, or said they
did.  They wanted "conservative" characters and often equated characters whose
evolution was affected by natural selection with ones which could change very
rapidly in response to natural selection (for example, superficial color
patterns or size of the organism).  Of course there are also characters
affected by natural selection that change with great difficulty and only once
in a while.  (For example, if the conditions causing or allowing the change
are infrequent).

>                      However, in practice this is only weakly followed
> at best.  Most systematists that I know have openly admitted that they use
> whatever character that is most helpful.  

They in practice are more biologically sensible than their formal
prescriptions.  In practice they made an intuitive assessment of how rapidly
a character could be reversed by local and temporary selection.  If so,
the character was likely to show parallelism and reversal and was best
dropped.  But a character like having a placenta was retained even though it
was most probably caused by natural selection, because the conditions for
getting started on having one are most likely unusual and hence rare.

Taking a statistical view this makes sense as the rarer change is the more
heavily the character should be weighted if you are (for instance) doing a
parsimony analysis.  You will find a fairly detailed discussion of this in my
1981 paper in Biological Journal of the Linnean Society, on the logic of
character weighting.

> 	a) if the characterization of the traditional approach to
> 		character selection appropriate?

See above.  In short, sort of.

> 	b) if so: why is it thought that the separation of the causes
> 		from the process necessary?

I don't think traditional systematists were really trying for that, as
mentioned above, but recent phylogenetic systematists have been explicit
about trying for it.  As they have argued (I believe incorrectly) that
use of the unweighted Wagner parsimony method guaranteed this.  They have
wanted to escape from having to know the mechanism of evolution which they
consider as unknowable.  By holding that the only valid method of phylogenetic
analysis does not depend on knowing evolutionary mechanisms they have
held they have esacped from knowing this, and since they tend to view
the same data sets as the only possible source of knowledge about evolutionary
mechanisms, they have as a result argued that those mechanisms are
intrinsically unkknowable.  The extreme of this view are the pattern cladists,
but other members of the phylogenetic systematics school have also argued that
processes are unknowable and unnecessary to know.

More recently (in the last few years) there has been increased interest
in the ranks of phylogenetic systematists in character weighting, and this
is re-opening the question.  

> 	c) lastly, how does this philosophically affect someone who
> 		desires to include behavior into their phylogeny?
> 		-does it mean that we should look for behav. patterns
> 			that presumably evolution doesn't act upon?
> 		-if so, how can we characterize those patterns that
> 			are immune from evolution's action?

I think it should be clear from the above that I agree more with the
traditional systematists except that I feel that their practice (if not
always their prescriptions) can be illuminated by a statistical approach.
They would not have absolutely banned behavioral characters.  If they
are something encoded in the genome we could use them especially if we
had some way of assessing or guessing their relative probabilities of
change.  For instance, most systematists have felt that the fact that
crocodiles sit on nests and sing is a valid indication of their having common
ancestors with warblers (and other birds).

The contemporary phylogenetic systematics school is only now groping its
way toward agreement with this view, but if Danoff-Burg adopts it he may still
encounter resistance from the folks on the platform at Hennig Society meetings
even though many in the audience will quietly agree with it.

As he will realize, my own view, although gaining among that audience, is still
regarded as heretical (and worse).  Nevertheless evolutionary mechanisms and
statistical inference frameworks are currently sneaking in the back door
of the house of phylogenetic systematics.

It would be nice to have a posting here from a more orthodox defender of the
views of phylogenetic systematists, as that is the dominant school in
contemporary systematics and the view I am presenting is not theirs.

-----
Joe Felsenstein, Dept. of Genetics, Univ. of Washington, Seattle, WA 98195
 Internet:         joe at genetics.washington.edu     (IP No. 128.95.12.41)
 Bitnet/EARN:      felsenst at uwavm
 UUCP:             ... uw-beaver!evolution.genetics!joe




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