🚀 go-pugleaf

Isn't just my signature convincing enough?  :-)

	I have been asked to explain further my recent comment here
that:

	Any sort of heavy negative selection (large parasite load) can
        cause speciation.  This has been shown in Tom Ray's Tierra stuff.
        If some host's dodge one way, and some the other, it can
        eventually lead to incompatibility.

Tom Ray's work has been published in the Sante Fe Institute's 
proceedings for their Artificial Life conferences.  I don't have
the paper's handy, so I can't check them right now.  The work
I am referring to may be unpublished (I saw it as a demo when
I was an undergrad at Delaware)

In Ray's system, the organisms are essentially asexual (although 
recombination occasionally occurs).  If in his system you start with
only a parasite and it's host, new forms of the host quickly arise,
(which are immune) to be followed by new forms of the parasite.          
(which can parasitize the new form).  Thus what I suggested probably
holds true for asexual organisms -- strong negative selection can
cause speciation.

What about for sexual species?  Well, the same should apply IF
the "dodges" used by different variants affect the fitness of
hybrids between those variants, such as changes in reproductive
structures (macro or micro), alterations in the timing of reproduction,
gross genetic rearrangements, etc.  


Keith Robison
Harvard University
Department of Cellular & Developmental Biology
Department of Genetics / HHMI

robison@biosun.harvard.edu