🚀 go-pugleaf

[Disclaimer:  I have missed the beginning of this thread.  If I repeat
anything below which has been said before, I apologize in advance.]

In article <1992Dec16.144720.18569@husc3.harvard.edu> robison1@husc10.harvard.edu (Keith Robison) writes:
>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I am referring to may be unpublished (I saw it as a demo when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 exactly does "negative" selection mean?  I would argue that
selection is selection:  some genotypes are more likely to reproduce
than others.

As for parasites leading to speciation, I suppose it depends on how
you define "species" in the case of asexual organisms.  The definition
above seems to be, "any new genotype."  Mind you, I am what W. D.
Hamilton has referred to as a "host-parasite coevolution freak"
myself, and I'm glad when anything can be explained in terms of
parasites :-), but it doesn't seem like any sort of new mechanism has
been offered here; since "incompatibility" means nothing in an asexual
population, there's no need for it here.

>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.  

Here's where "incompatibility" is more likely to become important.  I
would argue, however, that any "revolutionary" strategy for avoiding
parasitism (or any other strong selective pressure) would spread
rapidly through a sexual population, and not cause speciation unless
there was significant population subdivision.  If population
subdivision was being assumed, I apologize for reinventing the wheel.

>Keith Robison
>robison@biosun.harvard.edu 
-- 
--Andy
     "God is a real estate developer / with offices around the nation
          They say one day he'll liquidate / his holdings on High
             I say it's all speculation." -- Michelle Shocked