On Thu, 15 Apr 2004 23:44:55 +0000 (UTC), "Malcolm"
 wrote:

>
>"r norman"  wrote in message
>>
>> Another way to look at it is as a random walk process.  Evolution
>> tends to spread out organisms in all directions.  However, it started
>> with simple things and there is a lower bound to how simple an
>> organism can be and still be alive.  So there is necessarily an
>> increase in average complexity with time. Still, most things remain
>> simple.
>>
>This was Sephen Gould's argument. The problem is that a "random
walk" could
>only produce something that looked random - big agglomerations of cells
>maybe, but to exquisitely structured into a co-operative organism.
>It is true that some simple solutions to the problems of living still work.
>However for a substantial subset of organisms the more complex form offers
>an advantage. For instance, jawed mouths are more complex than jawless
>mouths and look longer to evolve. However the jawed fishes have radiated to
>fill a huge variety of niches, and even spread to the land, whilst the
>jawless solution is only viable in a few specialised niches, such as the
>parasitic hagfish and lampreys.
>
>
A number of people have commented on my statement about evolution as a
random walk with no specific tendency to evolve towards more
complexity.  Here is a better description of what I was trying to
explain.

Imagine an abstract "phenotype landscape" spread out, each point
representing one possible type of organism. Imagine it organized by
"complexity", something we can't really define or measure but we know
it when  we see it.  On one side are the simple things, on the far end
are the most complex.  There is a wall on the simple end -- too simple
and you can't sustain life.  We don't know (or haven't reached) a wall
on the complex end.  In the beginning, you start with a bunch of cells
all bunched along the wall at the simple end.  Evolution is a random
walk.  There is no specific tendency to get more complex nor is there
any specific tendency to get less complex.  There is only a tendency
to change, to move from where you are to another location.  The
changes are random in direction; a "drunkard's walk".  Over time,
organisms tend to fill the landscape, spreading out over everything.
As time goes on, organisms spread farther and farther into the complex
region.  The leading edge always gets more and more complex.  The
average always gets more and more complex.

Still, the mechanism of evolution in no way demonstrates a tendency to
produce complexity.  The mechanism of evolution is to produce and
select for change.  The "move towards complexity" is simply a product
of the diffusion process (the random walk) and the boundary conditions
(a barrier at the simple end) and the initial condition (start
concentrated at the simple end).

The existence today of a huge variety of less complex organisms (most
genomic variability lies in the prokaryotes) shows that there are
enormous numbers of habitats and niches where simple shows a high
degree of fitness. On the other hand, there are enormous numbers of
niches where complex shows higher fitness.  We rather large
terrestrial organisms tend to focus on the latter, completely
overlooking the former.  If we were microscopic aquatic organisms, we
might have a different perspective.
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