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

> "> <quote>On the basis of much evidence, scientists
> > have concluded that mutations occur randomly. The term "random" here has
> > a specific meaning that is often misunderstood, even by
> > biologists. What we mean is that mutations occur irrespective of whether they
> > would be useful to the organism. Mutations are simply errors in DNA
> > replication. Most of them are harmful or neutral, but a few of them
> > can turn out to be useful. And there is no known biological mechanism
> > for jacking up the probability that a mutation will meet the current
> > adaptive needs of the organism. Bears adapting to snowy terrain will
> > not enjoy a higher probability of getting mutations producing lighter
> > coats than will bears inhabiting non-snowy terrain.</quote>

Actually, the probability of a mutation being harmful, neutral, or
beneficial depends on the starting point and the "goal" as well. For
example, if the bears adapting to snowy terrain were black bears,
almost any mutation affecting their color would improve their match to
the background. This does not affect the likelihood of the mutation
happening but rather the likelihood that it will be successful if it
comes. (This is probably gross oversimplification, as other factors
besides match with background are likely to influence bear color, such
as mate preference and ability to absorb or reflect heat).

> A couple of months ago, a (non-scientist) friend of mine mentioned the following lizard experiment (see: http://www.dinosauria.com/jdp/evol/lizard.html for a
> quick summary, though I suspect you're already familiar with it) in which a study intended to understand extinction ended up producing rapid evolution on the macro-scale.

> Now, if evolution is really "random" in the sense that there is "no known biological mechanism for jacking up the probability that a mutation will meet the current adaptive needs of the organism.", how is it that these lizards were able to mutate in exactly the needed way in a relatively short amount of time? (even given that they probably have faster reproduction rates) I can think of at least two hypotheses: 1) the new environment increased the stress levels of the lizards, influencing the chemical and hormone levels in such a way as they triggered an increase in the frequency of mutations (i.e. the difference between scribbling a note quickly versus carefully crafting a letter), therefore increasing the likelihood of mutations and/or 2) the lizards already had the DNA for the adaptations they needed, but it was dormant until triggered.<

> Have these possibilities been studied, and if so, are they supported? Even if true, (particularly in the case of hypothesis #1), would it be an adequate mechanism to produce the observed evolutionary effects in such a quick time period?<

An additional factor is 3) competition may have been lower in the new
habitat (fewer lizards), making it easier for mutants to survive and
evolve towards a novel form.

 I don't know what has specifically been examined in the lizards. The
fact that the same sort of morphology appears repeatedly (not only in
the experiment but also naturally in species of lizards throughout the
Caribbean) strongly suggests that some version of 2 plays a
role-whether it's exactly latent or else only a few steps away.
Interplay between the genetic ability to readily adapt and the
opportunity/pressure to do so would produce the result. Information
on the main selective pressures affecting the lizards would help
assess relative roles of stresses versus opportunities in the change.
Stress and opportunity can coincide, in that a situation in which
everybody is having a hard time can lower competition, just as a
situation where things are easy for everyone can lower competition.

> As for my friend, he concluded that this was God's work, not evolution's per se--wonder if he's right?

God did it according to a pattern describable as evolution, so it
depends on what level you look at. God's role is much more important,
but that does not make a properly restricted crediting of evolution
wrong.

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