Re: The Drunken Sailor's Stumble

["Tim Williams" <twilliams_alpha@hotmail.com>]

David Marjanovic wrote:


> Drift? If I have understood the book correctly and there aren't too many
> gaping holes in my English, then Gould writes that the major theme of
> evolution is diversification into all directions, not only that of "higher
> complexity", and that there is no necessity for complex (to whatever 
> degree)
> life to evolve once life has appeared.

I don't agree with this interpretation.  I think increasing complexity may 
be be adaptively advantageous and, therefore, be positively selected for.  
Think of the benefits of being a multicellular lifeform in which discrete 
groups of cells are devoted to a single function: procuring nutrients, 
digesting nutrients, respiration, movement, reproduction.

I like to think that the reason us humans have a mouth, a gut, a brain, a 
heart, two lungs, two arms, two legs, reproductive organs (and an 
endoskeleton to connect them all to) is the result of positive selection, 
and not because of random diversification.

(I know the development of multicellularity and apportioning of functions to 
organs are just two parameters of increasing complexity, but they do 
represent increasing complexity nonetheless).

> ", and that there is no necessity for complex (to whatever degree)
> life to evolve once life has appeared.

On the contrary, I think it is probably inevitable - at least on Earth.  On 
some anoxic, sulfur-choked, volcano-ridden moon of Jupiter or Saturn (or 
some far away planet we haven't discovered yet) the metabolic and 
morphological possibilities may be more constrained.  But even in microbial 
biofilms here on Earth there is some rudimentary "division of labor".  
Bacterial colonies may exploit the benefits of certain cells specializing in 
certain functions to the advantage of the entire colony.

> > In fact, Gould's own
> > discussion on the evolution horses in the book (which correctly rebuts 
> the
> > view that equid evolution was *not* governed by forward progress) tends 
> to
> > undermine his assertion that diversity is not due to adaptive advantage.
>
> Is there one negation too much in this sentence?

Nope, there is not.  I agree with Gould's interpretation that horse 
evolution does not emulate progress, but it does examplfy diversification.  
I disagree with Gould's notion that this diversification was mostly a 
consequence of drift rather than selection.  At least, that's the point I 
thought he was making.  It was certainly the overriding theme of _Full 
House_.


Tim

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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