Sorry everybody,

[Nick Thompson]

If the formatting did not survive your server, the attachment has exactly the same message.

N

Nicholas Thompson
nickthompson at earthlink.net
http://home.earthlink.net/~nickthompson


----- Original Message -----
From: Nicholas Thompson
To: friam at redfish.com;Jaan Valsiner;ppgb at cam.ac.uk;lrudolph;dwilson at binghamton.edu;rsokol at clarku.edu;echarles;elescak;sbarr;jogreen;Gbarker
Cc: w-wimsatt at uchicago.edu; jcshank at ucdavis.edu
Sent: 5/20/2006 5:17:39 PM
Subject: Generative Entrenchment and the Possiblity of Inheritance.


Dear Loose group of Correspondents,  
 
For a couple of years now, you all have been suffering with my inability to state what seems to me a fundamental paradox arising from the Developmental Systems Theory: that natural selection is impossible without inheritance and inheritance seems increasingly impossible given the complexity and chaos of developmental systems as we are coming  to know them.   I have just come across a clear statement of this paradox in Wimsatt, W. C. and Shank, Jeffrey C. (2004).  Generative entrenchment, Modularity, and Evolvability; When Genic Selection Meets the Whole Organism.  In, Schlosser, G. and Wagner, G. P.  Modularity in development and evolution.  Chicago: University of Chicago Press.   The title would seem to suggest that the problem they identify relates ONLY to the relation between the organismic and the genic level, but in fact it is potential troublesome at all levels of selection.  
 
The generative structure of the system (including the organism plus relevant aspects of its environment) has a characteristic set of causal interactions which could be variously represented.  One of the simplest representations is a directed graph, where nodes are parts, processes, or events, and arrows are consequences of the presence or operation of notes on other nodes.  For each node, consider how many other nodes can be reached from it by following the arrows.  This indicates how much of the phenotype is downstream of, causally dependent on, or affected by a given node.  We define Generative Entrenchment as the magnitude of this downstream dependence.  [Page, 360, Caps and italics by nst]
 
Darwinian processes should almost inevitably give rise to generative structures (Wimsatt 2001).  However, we are still left with two perplexing questions:  How can complex adaptive systems evolve and continue to evolve in any other than a predominantly accretionary way if their generative elements become increasingly entrenched with increasing complexity (Shank and Wimsatt 2000). How does this permit continued modular evolvability? It is no surprise, therefore, that fundamental research focus of the evolutionary sciences is to figure out how complex systems can continue to evolve when evolutionary processes generically give rise to entrenched structures.  We call this the G[enerative] E[ntrenchment] paradox.  [Page 363
 
In these passages, Wimsatt and Shank lay out with perfect clarity the problem I have been fumbling with.  However, by focusing on Generative Entrenchment, they conceal one startling implication that I see in their view (possibly because they don’t believe it).   Generative Entrenchment threatens Natural Selection because Natural Selection requires some sort of inheritance, and, so far as I can see, any trait that is Generatively Entrenched cannot be inherited at the level at which it is entrenched.   I think I perhaps have a solution to this problem, but I will hold off offering it until I have convinced anybody of the existence of a problem to be solved.  

I apologize for intruding on your otherwise Peaceful saturday.

Nick


Nicholas Thompson
nickthompson at earthlink.net
http://home.earthlink.net/~nickthompson
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