>1. First, I assume that you mean *natural selection* when you refer to,
>*evolution* and not just some vague notion of *change*. (If my assumption is
>not correct please let me know. I believe it is necessary to agree on what
>we mean by *evolution* to have a productive discussion.)
I am not sure how to answer this. If my post on limits to change does not
tell you what I believe, try to ask this again.
> Natural selection
>means that a number of random mutations must have taken place in the germ
>line of the panderichthyid fish in order for it to take the very first steps
>toward becoming a tetrapod. Let's take the mutations that resulted in the
>"the humerus, ulna and radius in the forelimb and femur, tibia and fibula in
>the hindlimb." Why would the initial mutation that started this transition
>from fins to legs have ever occurred and been selected in the first place?
No one can know why, but I can speculate. The life-style of the
panderichthyids seems to have been in shallow water (see Ahlberg and Milner,
nature 368, p. 508) where they needed rapid movement to grab their prey. The
paddle-like arms with radius-ulna-tibia-fibula may have let them move more
rapidly by pushing off the solid bottom rather than pushing against soft
flowing water.
> It would only have interfered with the adaptation of the fish to its aquatic
>environment, wouldn't it? Since natural selection has no plan or purpose for
>the future, such a mutation would seem to be useless, even detrimental when
>it first appeared. If this is true, would it not have been immediately
>eliminated from the gene pool?
If the prey were faster than a fin could move the predator, the mutation would
have been advantageous not detrimental. Remember to catch prey often requires
rapid movements of very short duration. A frog sitting still moves his tongue
very rapidly when a fly comes near. The more rapid the tongue the more
successful the catch. Same with a fish in shallow water catching smaller
fish.
>2. I assume that the panderichthyid fish was better adapted to its aquatic
>environment before the beginning of its transition to a being a tetrapod than
>it was in its initial move to land. Why, then, did it not stay put where it
>was, rather than migrating to a new environment for which it was not
>initially as well adapted? Land is a more difficult environment than the
>ocean, as J. Z. Young says (The Life of Vertebrates, pp. 14-16). Even if
>there were swamps and pools to help the fish make the transition, it probably
>remains true that their current adaptation to the ocean was easier than their
>initial adaptation to any new environment.
My understanding is that the Panderichthyids were fresh water not ocean going
animals. They are found in the Old Red Sandstone equivalents of Greenland and
Scotland. I know that this is a continental/freshwater deposit. Life invaded
the land by moving up the rivers and swamps. Because of this, the
saltwater/freshwater transistion had already been made; but that transition
was unlikely to leave a mark in the record.
> You refer to evolutionists as
>saying: "evolutionists say the tetrapods were attracted by the food." Is
>that true? If so, how do they know it's true? What food? Arachnids and
>snails? What evidence is there that food on land was more plentiful and
>better than food in the ocean.
First off the land food does not have to be "plentiful and better than food in
the ocean". It merely has to be enough to feed them. Why do Norway rats live
in Tuscon? It is not that the food is more plentiful than where they were
originally from, but it is enough to feed them.
Secondly, This is the thinking on the environment of the upper devonian
continent.
"Whether or not the above scenario is correct, the Old Red Sandstone
continent of the Devonian (essentially the present-day North America pluse
north-west Europe) saw the subsequent development of extensive terrestrial
vegetation and of several terrestrial animal phyla. The Devonian flora was
cosmopolitan and contained, as well as the 'Rhyniophyta', present in the
Silurian, Bryophyta (liverworts), Lycophyta (club-mosses), Sphenophyta
(horsetails) and Pteridophyta (ferns)....the plants effectively created
cryptozoic niches that allowed the evolution of small, desiccation-intolerant
animals. Dominant among these were myriapods and early hexapods, all
presumably feeding upon detritus." Colin Little, _The Terrestrial Invasion_,
(New York: Cambridge, 1990), p. 9-10.
Now obviously I did not run an opinion poll on the food preferences
among the early tetrapods, but the food was there for the taking and it is a
reasonable inference.
> In sum, how does natural selection explain
>the migration from an easier environment to which the fish was well-adapted
>to a more difficult one?
>3. This is all part of a more general problem that Mivart posed during
>Darwin's day, as you know: How does natural selection account for incipient
>stages of useful structures? To use your example, how do you account for the
>incipient legs between the time that panderichthyid had fins and the time
>they became full-fleged legs?
The same thing that happens between the two species of monkey flower. A few
mutations create major deformities among the fins. However, the animal
refused to die and lived with his "disability" (only 7-8 bones in the "fin')
rather than the normal hundreds. If you want to see a modern example of a
"deleterious" deformity in which the animal refused to follow its scripted
role to die, look at the Goldschmidt toad. This toad had his eyes on the roof
of his mouth. He was found in a Canadian garden happily eating bugs.("Down in
the mouth - a 'Goldschmidt toad which, despite its remarkable development
alteration, was found doing well in a garden in Hamilton, Canada."Nature Feb.
2, 1995, p. 398.)
I do not know if this is heritable but the point is that this deleterious
mutation or development, did not deter this toad from living. (Shame on his
dirty little heart).
> Gould says Mivart's question has never been
>answered. Do you agree?
NO see my post on limits to change. The Sante Fe Institute is doing a lot of
work in this area. Mivart didn't have any knowledge of nonlinear systems.
That has only been developed in the last 25 years.
>4. How would a non-Darwinian like me try to explain the transition you
>described? That's a tough question. I too, like you, want a larger,
>historical context. In fact, I want a cosmic one. I believe the universe
>was created by God for the final purpose of bringing into existence human
>beings on earth (and possibly on other earths, maybe in alternate forms),
>whose purpose, to paraphrase the Westminster catechism, is "to know God and
>enjoy Him forever." The Big Bang, all the cosmological constants, the large
>number coincidences, the origin of life, the transition from aquatic to
>terrestrial life, the parade of vertebrates leading to and culminating in
>human beings, are all driven by that purpose. It is very difficult for me to
>use Darwinian evolution as a large explanatory framework because of its
>avowed purposelessness and materialism.
I do not believe it is purposeless. God designed the phase spaces (see my
limitation to change post). God determined what the world of living systems
would be like by this means.
> I do not find it possible to explain
>the transition of fish to terrestrial life in an evolutionary, purposeless,
>materialistic framework which I believe Darwinian evolution is. How do you
>deal with this unabashed purposelessness and materialistic naturalism of
>Darwinian evolution?
see the other post.
>5. To explain the transition from aquatic to terrestrial life in
>non-Darwinian terms, I would use principles of development, expanded to
>include the development of large groups of animals as well as individuals. I
>find developmental principles, more compatible than Darwinian mechanisms for
>dealing with the transition you described, and other changes in the fossil
>record.
If by this you mean what is happening in the case of the Monkeyflower, then I
would agree. The mutation changes the developmental pathway. Evolutionists
are already using this mechanism to explain evolution. Scott F. Gilbert
writes:
"How, then, can one modify one Bauplan to create another Bauplan? The
first way would be to modify the earliest stages of development. According to
von Baer, animals of different species but of the same genus diverge very late
in development. The more divergent the species are from one another, the
earlier one can distinguish their embryos. Thus, embryos of the snow goose
are indistinguishable from those of the blue goose until the very last stages.
However, snow goose development diverges from chick embryos a bit earlier, and
goose embryos can be distinguished from lizard embryos at even earlier stages.
It appears then, that mutations that create new Bauplan could do so by
altering the earliest stages of development."~Scott F. Gilbert,Developmental
Biology (Sunderland, Mass.: Sinauer Associates, Inc., 1991),p. 831-832
> For me principles of development apply to changes in the great
>animal phyla as well as to individual organisms. Development has several
>critical characteristics that make it a better candidate than evolution for
>explaining transitions and other phenomena in the fossil record.
As far as I can see, developmental pathway changes via mutation are a major
means of evolution taking place. I don't see the difference between what you
propose and evolution.
> It is
>*end-directed* and *purposive* as Mayr noted; the goal is the sexually mature
>adult. It is *internally driven* largely by genetic instructions. That is,
>it is largely *autonomous from the environment*. It is *hierarchically
>organized,* as von Baer asserted long ago (1828), with the general
>structures, most common to the phylum to which the organism belongs,
>appearing first in embryogenesis, and more specific structures appearing
>later and emerging from the general structures. The germline posseses
>developmental programs that are expressed over time in the offspring of the
>phylum. The individual genome is inherited from the germline, thus forming a
>*seamless genetic connection* with the history of the phyletic lineage.
> Individual development provides a window on phyletic developmment. As much
>if not more change in the biological world comes about by evolution than by
>Darwinian mechanisms. In development the *form* of an organism appears
>before its *function or behavior.* In this view the *form* and *structure of
>legs* in the panderichthyid fish developed first, followed later by its
>*function* of terrestrial behavior.
So why isn't this evolution? That is exactly what evolutionists think
happened. The evolutionist thinks that the form came first in the legs then
the use came later.
"Note that the forelimb of Acanthostega is
more fish-like than the hindlimb and could probably not be
brought into a weight-bearing position."~P. E. Ahlberg, "Tetrapod
or Near-tetrapod fossils from the Upper Devonian of Scotland,"
Nature, 354, Nov. 28, 1991, p. 301
> Development is more compatible with a
>purposive Creator, IMHO, than is purposeless Darwinian evolution. I like to
>think of development as the process by which the Intelligent Deisgner brought
>biological design into the world.
Not if you view the DNA phase space the way I do. See the limits to change
post.
glenn
Foundation,Fall and Flood
http://members.gnn.com/GRMorton/dmd.htm