Three-taxon analysis

pierre deleporte pierre.deleporte at UNIV-RENNES1.FR
Wed Apr 9 13:04:26 CDT 2003

A 12:40 08/04/2003 +0200, René Zaragüeta i Bagils wrote :
>( P. Hovenkamp wrote ):
>"Apart from that, my point stands: if any of these proposed mechanisms 
>results in a particular pattern of sister-group relationships, we may 
>reasonably hope that we can find that pattern by studying the characters 
>of the taxa. Of course, many of these mechanisms will result in very 
>similar-looking patterns of relationship, and that is why there still
>may be controversy and uncertainty"
>We agree. Now you talk pattern. Mechanisms come after, this was what I tried
>to say.

Well, seems that Peter talks "mechanisms" first, and thus evolutionary 
models first, not "pattern" for pattern's sake first, contrary to 3TA.
Strange indeed that René reads exactly the reverse than Peter's words mean...

Now, René further wrote :
>The point is that the ultimate source of knowledge are not observations. 
>This is not my idea, but Karl Popper's. You cannot learn anything from 
>observations alone, you need a theory FIRST to know what to observe 
>(observations can only be tests of theories).

Yes René, you get it: theory first, mechanisms first, evolutionary models 
first, not just-so patterns first (not even 3TA patterns).

>So the study of complex things is often complex.

But much simpler when conceived logically. You really need a theory of 
evolution in order to infer the patttern of evolution. If not, then you 
will infer a pattern of what? (Please don't just answer "relationships", 
"cladistics", "hierarchy" and "improved precison").

Otherwise, Peter Hovenkamp wrote :
"Owen's derivation of vertebrate parts does not make sense in a 
non-evolutionary world. It is
one of the "explananda" of which evolution is the "explanans".

and David Williams answered :
"Yes it did make sense to Owen and many others, after all much 
'homologising' was done during that period (theories which still stand the 
test of time). You seem to have indulged in
judging Owen and his contemporaries by our standards, which is the wrong 
way to do it -- and which why I used the example."

I think it's likely that Owen's views "made sense" some way in his world, 
in his own "theory of life" (creationist ?), however difficult for us to 
conceive exactly what this sense may have been. But they do not make sense 
in the world of evolutionary theory, even if some vertebrae happen to be 
identifed as "similarities" in both worlds.

A frequent mistake of some phylogeneticians is to consider that the 
similarity between some pre-evolutionary homologies and post-evolutionary 
ones demonstrates that we can dispense with the theory of evolution in 
order to identify self-standing "homologies". As if indisputable homologies 
were just features to be observed in the real world out there without any 
theory of life in mind. The further step is this way is the ill-conception 
that these "obvious homologies" could be dealt with an "obvious procedure" 
in or der to reveal an "obvious hierarchy of life", to be explained afterwards.

Fortunately, René (himself !) reminds us that theory comes first, not 
"observation" like that. I am thus pretty certain that René is now able to 
dig out the necessary theory of character evolution standing behind 
three-taxon-analysis, or alternatively to aknowledge the lack of it. Such a 
theory is nevertheless presently completely missing in the whole 
three-taxon-analysis literature.

((Another post of mine entitled "3TA..." just appeared on the list, dated 
from 7 April because of problems with our local mailing system.
It talks of semantics -peculiar acception of "phenetic" in the 3TA literature-
and of lack of explicit evolutionary models in 3TA)).


Pierre Deleporte
CNRS UMR 6552 - Station Biologique de Paimpont
F-35380 Paimpont   FRANCE
Téléphone : 02 99 61 81 66
Télécopie : 02 99 61 81 88

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