I find it difficult to respond to your questions and comments piece-meal. As
I indicated to you in a private post, I will prepare a summary of my position
on phylo-development and send it out for comment from all. Meanwhile let me
say a few things about some of your comments and questions.
I tried to identify your position with regard to some clearly defined
meanings of the word "evolution." I suggested that "change through time", the
most inclusive definition of evolution, fairly describes your position. You
reponded:
"I would object here. My post was specifically aimed at showing that there
is NO limit to change via mutation. As such, I did not feel the need to
raise the natural selection issue in that context."
I am puzzled. I don't know what you are objecting to. Isn't change
through time what you are describing for yourself. Second, I have never
heard the claim made that there is no limit to via mutation, except from
people like Dawkins and Dennett. Your model may show it where I can't find
it; where is the empirical evidence to support your statement? There are
boundaries and limits to the amount to change that can be wrought in the
biological world. The fact that body plans, on the whole have not changed,
or at least one phylum has not changed into another one since the Cambrian,
would suggest that mutational change is not limitless.
Further, evolutionary theory calls for a selecting agent. Your limitless
muational change does not have one. Do you define evolution exlusively in
terms of mutations sans selection?
I dwelt on the transition from aquatic to terrestrial animals and asked the
question about the fate of the *first* mutation that would initiate the
change fromm a fin to a leg. I questioned how such a mutation or series of
mutations would be adaptive since it would interfere with an already
well-adapted, well-functioning organ, the fin. You did not respond to my
question. Instead you went on to discuss front paws. What I want to know is
how you get to front paws in the first place when the very first mutation in
that direction is presumably inadpative?
On the other hand, if one assumes that there was a developmental program for
the transition from fins to paws, then the first step does not depend on
selection. The program simply drives the animal through the incipient
stages, come hell or high water, until the final stage of paws, or claws or
hooves has been attained. That doesn't mean that there wasn't any shaping of
the incipient stages along the way by natural selection. Developmment theory
holds that the main line of change was developmentally driven, with side
lines and adpative embellishments added by natural selection.
Your next question is the tough one. Did the germ line of the original
vertebrates contain all the genomic developmental programs for all the
subsequent fish, amphibians, reptiles, mammals, humans? Logically my
position calls for it. That's not to say that I'm comfortable with this
position. At this point I am assuming that the germ line genome of Pikaia,
one of the presumed first vertebrates, was rich in genomic developmental
programs even though its individual somatic genome was quite simple. A
small, simple body carrying a germ line that was loaded with developmental
programs.
In defense of this position, I refer to a hint made by Vefmeij in his
commentary on Wray, et. al.'s, article "Molecular Evidence for Deep
Precambrian Divergences Among Metazoan Phyla" in Science of 25 Oct. 1996.
Vermeij said, "Contrary to some perceptions of the Early Cambrian, *a large
array of developmental patterns* was already available when the momentous
spurt of the latest Neoproterozoic and earliest Paleozoic eras ensued"
[referring to the Cambrain explosion] (p. 526). It was developmental
programs that were synthesized in the Precambrian according to Vermeij's
comment which were then organized and ordered into the array of Cambrian
animals.
My second comment is that the structural developmental programs may not have
required as much space in the germ line as might be supposed since the genome
of mammals is made up of a large amount of silent genetic material. I
hypothesize that the developmental patterns suggested by Vermeij may not have
been physically very large or taken up large amounts of genomic space. I do
not know of experiemental evidence for developmental regions.
Another difficult problem I encounter is how to account for the sequence of
expression of the developmental program throughout millions of years. Why
did fish come before amphibians, which came before reptiles, etc? I have no
answer for this question.
Were these phyletic developmental programs immune from mutations, you ask? I
would say yes, just as the developmental programs for the body plan
apparently are. They have lasted with little or no change for hundreds of
millions of years. Or they may have unusually effective repair mechanisms.
But the position that a series of developmental programs drove the main
changes in various phylas suggests that the relatively sudden breaks between
the various taxonomic levels in a given phyla was produced by discreet
programs, acting in a more or less holistic manner, not by gradualistic
changes (or even punctuations) that is the hall mark of natural selection.
Still, many mysteries remain.
You asked, "Are you denying that natural selection operates? Is not the
development of immunity by disease causing bacteria a result of natural
selection?" I do not deny the operation of natural selection. I only say
that it works on a sliding scale. Early in the Phanerozoic, developmental
programs were in the driver's seat, and natural selection came along for the
ride, pitching in wherever it could. Starting in the Cenozoic, our current
era, natural selection gradually took over the reins of biologic change and
became the dominant force in the organic world because developmental programs
were all already in place and there were no more left to be expressed.
Development also works on a sliding scale. It starts out high, and ends
low. NS starts low and ends high.
Has the unfolding ceased, you asked. From my perspective, yes. There are a
finite number of developmental programs in a phyletic germ line, after which
no further developmental unfolding can take place. In fact, the germ line of
phyletic lineages begins to enter into a time of increasing decline and
disorder, after the developmental programs are played out. Note, for
instance, the large number of genetic diseases ascribed to the human germ
line, which does not suggest a lineal germline full of potential for the
future, but rather one that is gradually losing its steam and decling.
Did the immune system develop or evolve? The same developmental principles
apply. The early structure of the immune system arose exclusively through
developmental programs. (Dare I mention that the functioning of the immune
system is one of Behe's irreducibly complex biological systems? I have
argued with Behe that he should claim development as the biological process
underlying his irreducibly complex biological systems, rather than leaping
immediately to an Intelligent Designer.) The fine tuning of the immune
system was done increasingly by natural selection after the basic structure
and function was laid down by development.
I'll have to get a copy of Gilbert's Developmental Biology in order to
address vertebrate embryology. Can you give me the publisher.
I don't think I answered all your questions. But it's a start. I like your
questions. Obviously many of my answers are speculative, or hanging only on
a shred of evidence. That's where I am right now.
With appreciation,
Bob