"So it seems to me that you have not given much support for your claims.
Can you clarify for me what your assumptions are and what evidence you
have for them?"
Not without writing a book, but I'll see what I can do.
"Do we really KNOW that the function (resistance to X, Y, Z) NEVER existed
before? Has this been conclusively demonstrated? COULD it ever be
conclusively demonstrated? Is it absurd to suppose that at least some
organisms in a large population already had the function (due to the
presence of the protein, etc. needed for resistance) before the presence of
the toxin? Kevin, you appear to simply assume this and do not present an
argument to support it."
The mutations which create the proteins certainly have occurred before, but
that's another reason why I concentrated on function. If the mutations
occur each generation, only a small percentage of the population at any one
time will have that function. They will certainly try to pass the mutat
ions on to their own progeny, depending upon the vagaries of meiosis, but
with no selective pressure to retain the mutations the functions can be
lost be so-called back mutations that destroy the genes that code for the
proteins that provide the function. If the mutations occur less frequently
than once a generation, then it is likely there can be generations when no
one in the population has the mutations. 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. 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.
"The even stronger claim is made that such a function 'COULD NEVER exist
before'. Why do you believe this? If the only way the function could have
arisen were through a mutation, and if such a mutation occurred only after
the toxin or threat appeared, then you could make such a case. But this is
quite a stretch."
I did not literally mean that the necessary mutations only occurred after
the toxin appeared. However, what I said in the previous section goes
double here. Just as when I said that a function never existed before I
meant as a permanent part of the population (not as a fleeting phenomenon
that comes and goes but never stays), when I say that a function could
never have existed before I also mean permanently. The mutations that
produce the functions could appear and disappear at frequent intervals, but
the functions could never have existed permanently until DDT, nylon and
artificial antibiotics had been invented. And if they had never been
invented, then the functions could never have become permanent.
A function that comes and goes is of no use to a population; it must be
established permanently. For that to happen, however, the conditions the
function is meant to handle must be in place to provide the selection
pressure needed to make the function permanent. Until a function does
become permanently established, it does not exist and technically has never
existed, and if the conditions needed to make the function permanent never
occur, the function itself can never exist.
Kevin L. O'Brien
klob@lamar.colostate.edu