Re: [asa] Randomness in evolution (was Review of Behe in Books and Culture)

A couple of ways in which mutation rates can increase under stressful
situations may be of interest for this thread:

Although under ordinary conditions, high mutation rates are usually
detrimental, under stressful situations a high mutation rate may be
advantageous in that it occasionally hits on something useful (while
also producing a bunch of failures). Such a high mutation rate can be
generated by a mutation affecting genes involved in DNA copying or
error checking. Examples include bacteria that were engineered to not
process a particular sugar and then were given only that sugar.
Researchers were surprised when they took descendants of lineages that
mutated to regain ability to use the sugar and re-disabled them.
These regained the ability to use the sugar much more readily than the
original, and there was speculation about Lamarckian evolution until
it was figured out that the bacteria had high mutation rates across
the board, not a special ability for the selected feature. Another
example is dodging an immune system, as practiced by cancer, HIV, etc.

Another way to generate higher mutation levels in the face of stress
is to release previously undetected mutations, giving them more chance
to have an impact. This occurs because a number of proteins, often
called heat shock proteins, have multiple functions. Under ordinary
conditions, they help stabilize other proteins. In this role, they
can mask the effects of mutations in those proteins. However, they
also play a role in responses to high stress (such as heat, hence the
name). When they are pressed into duty to deal with a shock, the
other proteins have to manage on their own and accumulated mutations
may have an effect.

High variability is often associated with the early populations
expanding into new niches. This is seen in the fossil record in the
Cambrian radiation and in populations in the aftermaths of several
extinctions, as well as in some modern examples of new habitats
(species introduced into new areas; creation of a new lake; etc.).
This would fit with a release from competitive pressure allowing
mutants a better chance to survive and establish themselves-flattening
the adaptive landscape.

-- 
Dr. David Campbell
425 Scientific Collections
University of Alabama
"I think of my happy condition, surrounded by acres of clams"
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