"You don't usually need to wait on random mutation. Most populations maintain a significant amount of variation at any one time, and thus can respond, often on time scales of a few years or less, to sufficiently extreme selective pressures."
Having less amount of variation in the population is the _opposite_ of evolution. In addition, what evidence is there that the variation is the result of random mutation? This is assuming the conclusion.
In addition, are you sure that in the example you give, there is positive evidence of either random mutationor of selection being the reason for the variation? I've read lots of papers that simply use "selection" for any of a range of phenomena, some quite distant from the ideas that Darwin put forth as "natural selection" (i.e. differential survival and differential reproductive ability).
Huh? How do you figure? By at least conventional definition any populational change in the organism is "evolution". Less variation, more variation, the same amount of variation but a different mix of genotypes -- its all evolution.
Besides, this state of affairs isn't permanent. If an organisms is subjected to strong selective pressure that will tend to lower the total variation in the population (at least for the selected trait) but once a new adaptaptive peak is reached variation will re-accumulate about the new mean.
In addition, what evidence is there that the variation is the result of random mutation? This is assuming the conclusion.
Again, HUH? You wanna just throw out population genetics entirely? (This would make you a bit of an oddball even among creationists.) Evidence? Thousands and thousands of experiments, both on wild and laboratory populations, documenting the spread of mutations through populations, and documented that this occurs in accordance with the core equations of population genetics.
In sum, mutations DO occur. This is a fact. At least some are beneficial, neutral, and/or only weakly deleterious. This is a fact. According to the extraordinarily well confirmed formulas of population genetics some portion (the probabilities are definite) of such mutations MUST become fixed in the population.
are you sure that in the example you give
??? I didn't give an example. I just said in general that there is available variation in a population/species, allowing it to evolve much faster than if it had to wait on new mutations to occur. This is uncontroversial even to creationists. (Indeed they insist on it. Indeed they may claim this is the only kind of evolution that happens.)
either random mutationor of selection being the reason for the variation
Pinging Ichneumon in case he knows of an exception, but I think I'm correct is saying that "selection" is never the "reason" (in the sense of being the cause of) variation. Selection, as noted, will tend to reduce variation.
Mutation on the other hand does cause variation. What other mechanism do you propose, btw? Variation obviously exists. In many cases we can look at populations that we know absolutely must have gone through a severe population bottle neck as some stage (for instance species living on volcanic islands) and we know that the small progenitor population couldn't possibly have carried the total variation found in the current population.