But now a name just popped into my head which may or may not be correct. I want to say a prolific experimentalist named "Hall," publishing in major journals like Cell and The Journal of Molecular Biology and so on, had some results suggesting directed mutation. I also *think* this may have been around the early to mid 80's. After reading furball4paws quote from the latest Futuyma textbook in msg #123:
"Environmental factors may affect the rate of mutation, but they do not preferentially direct the production of mutations that would be favorable in organism's specific environment" p.26, 3rd edition.
I'm now *thinking* that *maybe* this was how the issue of Hall's (?) seemingly directed mutations in bacteria was eventually resolved: That is that some stress induced hyper-mutation mechanism kicked in, so the calculations saying that the mutations were too improbable to be random were wrong.
Warning: these are *very* hazy recollections.
This is the main problem with discussing science with those who are neophytes in science. There is almost always an exception, especially is biology. We have generalizations to help frame problems, but there are always outliers. It comes from trying to "force" order where there is only a semblance.
E.coli has what are called mutator genes. These genes produce a product that causes high levels of mutations to occur - say they facilitate mutations. But the mutations they "facilitate" are the same ones that occur naturally, just at higher frequencies. There are "hotspots" also in bacteria where high mutation frequencies occur, but again they don't do anything that doesn't happen naturally. I could dig up some references if you want them.
There are also quite different frequencies for mutation between genes. Some mutate at high frequencies (as high as 10^-4) and some are quite resistant and mutate only at lower frequencies (as low as 10^-9). Because of all this mixing together, it would be quite difficult to prove some direction in mutation.
Having said that, I have left out transposons (the infamous "jumping genes") since they are another complicating factor. Their mutation sites are known, but I can't see much predictability in this area. Perhaps there's a molecular biologist out there that can clear this stuff up?
Warning: these are *very* hazy recollections.