Re: Evolution of complexity

From: David C Campbell <>
Date: Mon Sep 26 2005 - 12:04:58 EDT

>Evolutionary trajectory now shows some familiar characteristics namely,
periods of stasis followed by periods of fast change. Using a somewhat
simplified concept of fitness one can understand how neutral evolution
can cross chasms of reduced fitness.<

This connects to the question of how evolution can predict both gradual
and punctuated patterns. The key is that different settings will favor
different evolutionary responses.

"If it ain't broke, don't fix it" is not only good advice for
overzealous do-it-yourselfers but also a good evolutionary principle.

If something works well, changing it is likely to be detrimental. The
impact of this depends not only on the magnitude of the effect of the
change, but also on the level of pressure experienced by the organism.
If competition is high and/or the environment is somewhat harsh, then
the pressure to stick with a tried and true genome will probably be
high and variants will probably lose out. However, if conditions are
really easy, then there will be more room for variants to survive.
Finally, if conditions are putting severe pressure on the existing
form, mutants may have a good chance of hitting on something better
than the standard form. Correspondingly, evolutionary stasis tends to
prevail in slightly unstable settings-enough to keep organisms on their
toes but not enough to push them over the edge. Another example is
the high variation seen in pets. Although the genetic changes to get
from a wolf to a miniature schnauser are quite small, the selective
pressure in the wild is much higher with regard to these changes than
it is in domestic settings.

The phrase "survival of the fittest" may be misleading in this regard.
The fit enough, not just the fittest, survive. Natural selection acts
strongly in the case of really bad options, i.e., fatal mutations.
Thus, a large unfruitful area of DNA sequence space is off limits to
evolution. However, the probability of mutation is not uniform
throughout the genome. There are several factors that affect the
mutation rate, both intrinsic to organisms and external (e.g., changing
levels of radioactivity and oxygen over time).

Dr. David Campbell
425 Scientific Collections
University of Alabama, Box 870345
Tuscaloosa AL 35487
"James gave the huffle of a snail in
danger But no one heard him at all" A.
A. Milne
Received on Mon Sep 26 12:07:05 2005

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