Yeast Mutation Vs. Harvest Starter

So, I've heard the rumor that "eventually" yeast will mutate to their environment and in fact, this is how "house" strains can be cultivated.

1st question: Is this really true? Really?

2nd question: If so, how many generations until you notice a difference?

Here's the background. I've had great luck at harvesting yeast. Especially Bell's yeast. My Two Hearted clone (turned barleywine) kicked major arse.
Now I'm giving a go at Oberon, like so many others... I'm harvesting the yeast as we speak in a starter. Here's the issue. I'm in the habit of using leftover wort runoff for my starters (after a good boil, of course). The question is (3rd I guess) the wort I'm using to harvest my Oberon yeast is from a dark amber batch. Will the Oberon yeast notice a difference in it's environment and mutate enough to cause a difference in flavor just from my starter? Or am I worried about nothing but hearsay and speculation

Forgive my verbosity, I'm a sixer of Oberon down. Cheers!
-B

Yes, it is true. Microorganisms evolve very quickly because they can go thru several generations in hours as opposed to years. I think it would many generations to notice a change, providing the yeast is handled properly.

handling the yeast properly is the key. the brewer at a local pub is up to about 150 generations (repitches) and has told me that things move very slowly when it comes to mutation (his experience). the wort you use to grow the yeast with doesn't seem to be a big deal. apparently he's looking to find the certain point where he really likes the 'current' characteristics of the yeast and then he'll consider banking it. i've only done about 30 rinse/reuse cycles and have only noticed a slight difference in attenuation. too many variables involved with homebrewing to really make a good assessment though.

The environment the yeast is grown in provides selective pressure on the yeast. The selective pressures will influence the yeast that will survive in the next generation. You have to assume there will be variation in population(major principle of genetics) and that the environment, among other things, will select for organisms with good fitness to survive to propagate. What it goes on to mean is that using a strain over time to brew specific recipes will respond to the recipes over time by allowing the yeast that better utilize the ingredients provided to out compete the less efficient yeast. Another example would be selecting for ethanol resistant strains. You brew the beer and the high ethanol will kill off the ethanol intolerant yeast while leaving, or selecting, the yeast that are ethanol resistant. Constant use of this technique can change the characteristics of the original strain you may have had. Continual use of that strain can and likely will be repopulated by a modified version. Microbes are constantly responding to their environments!