Thanks for your reply and explanation about mutations leading to
resistance functions in a population. I have a few follow-up questions:
1. Your first paragraph concluded:
"... So when I say that a function has never existed, I do not mean that it has
never appeared; rather I mean it has never before been a permanent part of
the population."
I hope you now understand my confusion. I was assuming that "appearance"
and "existence" could be used interchangably. Is there some technical
reason to distinguish these terms, or was your original statement somewhat
misleading? No offense, but it seems you are now saying something very
different from your original statement.
2. You stated:
" So there is a good chance no
individual had the function when the toxins appeared. More importantly we
can demonstrate experimentally that we can take plants, insects or bacteria
that do not have the function (so they cannot pass it on to their progeny),
introduce the toxin, and watch as their progeny develop resistance due to
mutation. The point is a function may appear and reappear more or less
frequently as the mutations themselves occur, but if there is no selective
pressure to retain the new function, it can be just as easily lost. "
Perhaps you could point me to a reference on one of these studies. If
such an experiment is done, and if the toxin is introduced into a population of
bacteria, none of which have the resistance function, don't they all simply
die? If not, how is it that they can live to produce progeny, unless they
already have some form of protection against the toxin? Perhaps there is
more than one protective function involved, but this is confusing to me.
It might be due to my ignorance of the methodology involved, so if you
could either explain it to me or point me to a good reference, I would
appreciate it.
3. Semantically there is a big difference between saying that a function
never could exist before the inttroduction of the toxin, and your much more
nuanced statement above:
"The point is a function may appear and reappear more or less
frequently as the mutations themselves occur, but if there is no selective
pressure to retain the new function, it can be just as easily lost."
To me, the argument that such a function, present by mutation BEFORE the
introduction of the toxin, "CAN be just as easily lost" in the absence of
the toxin to provide a selctive pressure, is QUITE DIFFERENT from the
absolute-sounding claim that the function "could NEVER exist". I don't
mean to pick on you, but this kind of semantic shift is what drives me
and perhaps others crazy at times. If the claim is conditional and tentative,
then it needs to be explained that way.
However, as a teacher, I know I am also guilty of this when I explain
concepts to my introductory physics class...so I live in my own glass house.
Anyway, your comments on the above would help me a great deal.
Thanks,
Stan Zygmunt