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Re: The Drunken Sailor's Stumble




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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