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On Tue, 19 Dec 2000 19:45:28 -0600, Susan Brassfield Cogan wrote:

[...]

[continued from "Re: the reptilian egg: a `construction project' design"]

CD>Excerpt of Chapter VI of Origin of the Species by Charles Darwin

Thanks to Susan for posting this. I will put CD> before Darwin's words
to avoid getting them confused with any replies that Susan may make.

CD>Organs of extreme Perfection and Complication
>To suppose that the eye with all its inimitable contrivances for adjusting
>the focus to different distances, for admitting different amounts of light,
>and for the correction of spherical and chromatic aberration, could have
>been formed by natural selection, seems, I freely confess, absurd in the
>highest degree.

Agreed! In what follows Darwin does not explain these at all.

CD>When it was first said that the sun stood still and the
>world turned round, the common sense of mankind declared the doctrine
>false; but the old saying of Vox populi, vox Dei, as every philosopher
>knows, cannot be trusted in science.

Rhetoric. If Darwin had an explanation he would not need to user
rhetoric.

CD>Reason tells me, that if numerous
>gradations from a simple and imperfect eye to one complex and perfect can
>be shown to exist,

If Darwin *did* have "numerous gradations from a to one complex and
perfect" he would have established its common descent.

But, as he himself said, he would not have explained the *mechanims* by
which this "one complex and perfect" arose "from a simple and imperfect
eye":

"In considering the Origin of Species, it is quite conceivable that a
naturalist, reflecting on the mutual affinities of organic beings, on
their embryological relations, their geographical distribution,
geological succession, and other such facts, might come to the
conclusion that species had not been independently created, but had
descended, like varieties, from other species. Nevertheless, such a
conclusion, even if well founded, would be unsatisfactory, until it
could be shown how the innumerable species inhabiting this world
have been modified, so as to acquire that perfection of structure
and coadaptation which justly excites our admiration." (Darwin
C.R., "The Origin of Species," 6th Edition, 1928, reprint, p.18)

And why would the "simple and imperfect eye[s]" still exist?

CD>each grade being useful to its possessor, as is
>certainly the case;

This is a truism, explaining nothing. *Everything* that an organism
possesses may be presumed to be "useful to its possessor".

CD>if further, the eye ever varies and the variations be
>inherited, as is likewise certainly the case

What actual *evidence* is there for this? This is just begging the
question.

CD>and if such variations should
>be useful to any animal under changing conditions of life,

Again, what *evidence* is there of such "variations"? And what
"changing conditions of life" are these exactly?

CD>then the
>difficulty of believing that a perfect and complex eye could be formed by
>natural selection,

This is not supposed to be about "believing". Darwin is supposed to be
giving a *scientific explanation* of how it happened. If he explained it, then
it would not have to be believed!

CD>though insuperable by our imagination,

If it is still "insuperable by our imagination" then Darwin hasn't
explained it.

This is all just *brilliant* rhetoric.

CD>should not be considered as subversive of the theory.

Of *course* it should. Darwin has not *shown* that the eye *did* or even
*could* vary and the variations be inherited. He just *assumed* all the key
points.

CD>How a nerve comes to be sensitive
>to light, hardly concerns us more than how life itself originated;

That is one of the *key* points. A light-sensitive nerve already is an eye of
sorts. How did it originate?

And how did all the other apparatus of the eye originate:

"But how did an eye or two arise? There is no evidence for any
transitional form, even if one were feasible. We are not treated to a
detailed account of the evolution of retina, cornea, rods and cones,
visual photochemistry, tears ducts, lids, muscles etc. Can such an
irrational and hollow hypothesis be called scientific? What
advantage, as far as natural selection is concerned, could accrue
from the starting of an eye when the materials forming it were not
yet transparent. In the human, coding generates biconvex lenses,
purposely free from blood vessels, and focusing apparatus which is
exquisitely refined. The eye must be perfect or near perfect.
Otherwise, it is useless. Of what survival value is a lens, forming an
image, if not intimately linked to a nervous system which will
translate that image into electrical form? Or a nerve without a brain
to interpret the data? How could a visual nervous system have
evolved before there was an eye to give it information? So
questions continue until all parts of the body are woven into a
single whole, a web of mutual necessity. Darwinism does not look
you squarely in the eye. It insists on faith in the unseen conversion
of one type of eye into another. Upon this faith a humble shrimp
imposes considerable strain. Moths, fireflies and Euphausiid
shrimps, creatures all active in the dark, have special compound
eyes which include a retina on which the multiple lenses focus at a
common point to form an upright image. These shrimps, which
seem to be, and are, classified as close 'cousins' to true shrimps,
employ lens cylinders which smoothly bend the incoming light so
that it all focuses at a common point, rather than forming multiple
images as most compound eyes do. This feat of optical engineering
has only been duplicated by humans in the last decade." (Pitman M.,
"Adam and Evolution," 1984, p.217)

CD>but I
>may remark that, as some of the lowest organisms, in which nerves cannot be
>detected, are capable of perceiving light, it does not seem impossible that
>certain sensitive elements in their sarcode should become aggregated and
>developed into nerves, endowed with this special sensibility.

Note the rhetoric: "it does not seem impossible"! And this is supposed to be
a *scientific* explanation?

*How* exactly did all this happen?

CD>In searching for the gradations through which an orgain in any species has
>been perfected, we ought to look exclusively to its lineal progenitors;

Agreed. If the eye is supposed to have descended with modification, it is no
use looking at at non-lineal progenitors.

CD>but this is scarcely ever possible,

*Why* is this "scarcely ever possible"? If the eye arose by gradual
increments, it should be possible to map out a continuum from "lineal
progenitors" just like anything else.

CD>and we are forced to look to other species
>and genera of the same group, that is to the collateral descendants from
>the same parent-form, in order to see what gradations are possible, and for
>the chance of some gradations having been transmitted in an unaltered or
>little altered condition.

OK. But Darwin doesn't even do that.

CD>But the state of the same organ in distinct
>classes may incidentally throw light on the steps by which it has been
>perfected.

Not necessarily. It is still necessary to explain *how* "the steps by which it
has been perfected" actually happened, i.e. by what *mechanism*.

CD>The simplest organ which can be called an eye consists of an optic nerve,
>surrounded by pigment-cells, and covered by translucent skin, but without
>any lens or other refractive body.

Agreed. But these already have the Pax-6 master genetic machinery:

"BECAUSE their construction is so different scientists have always
assumed that the multifaceted compound eye of flies and the single
lens eye of vertebrates evolved independently. However, this belief
has now been challenged Rebecca Quiring and Uwe Walldorf at the
University of Basel have found tantalising evidence that both types
of eye evolved from a common organ. Over hundreds of millions of
years, flies and vertebrates have retained the same genetic master
switch for eye development. The gene in question is called Pax-6;
one of a family that ensures that parts of the body emerge at the
right time and place in growing embryos. Developmental geneticists
have known for a long time that Pax-6 has a vital role in setting up
vertebrate eyes. Human and mouse embryos With defective
versions never form eyes or else have small eyes lacking irises.
Quiring and Walldorf identified a gene in the fruit fly drosophila
which is homologous or virtually identical to the Pax-6 genes of
humans, mice, quails and zebra fish. Bases are the molecular letters
that spell out the genetic code. Also, after consulting records of
fruit fly gene defects, the researchers found that the position of their
gene in the drosophila geno]ne matches that of a mutation called
eyeless, which makes fruit flies develop without eyes. In
vertebrates, Pax-6 codes for a protein, called a transcription factor,
which switches on other eye genes. It triggers a cascade effect
through a series of genes which, step by step, make cells
differentiate and build the emerging eye. In the fly Pax-6 has the
same role and triggers the same genetic developmental path, even
though the end result is very different. ...The Swiss group has also
found DNA sequences similar to Pax-6 in flatworms, which are
among the most primitive of animals to have eyes. Flatworms are
blessed with just two featureless patches of photosensitive cells,
called eyespots. If Pax-6 tums out to be crucial in forming these
simple organs that distinguish between light and shade, Walldorf
and his colleagues say that scientists must rethink the dogma that
eyes of invertebrates and vertebrates evolved completely
independently." (Luck-Baker A., "DNA Evidence of Ancestral
Age" New Scientist, 10 September 1994, p.15)

Gehring, et al., found that this Pax-6 was "a master control gene
throughout the metazoa", i.e. "in vertebrates, ascidians, insects,
cephalopods, and nemerteans", etc:

"The Drosophila gene eyeless (ey) encodes a transcription factor
With both a paired domain and a homeodomain. It is homologous
to the mouse Small eye (Pax-6) gene and to Aniridia gene in
humans. These genes share extensive sequence identity, the position
of three intron splice sites is conserved, and these genes are
expressed similarly in the developing nervous system and in the eye
during morphogenesis. Loss-of-function mutations in both the
insect and in the mammalian genes have been shown to lead to a
reduction or absence of eye structures, which suggests that ey
functions in eye morphogenesis. By targeted expression of the ey
complementary DNA in various imaginal disc primordia of
Drosophila, ectopic eye structures were induced on the wings, the
legs, and on the antennae. The ectopic eyes appeared
morphologically normal and consisted of groups of fully
differentiated ommatidia with a complete set of photoreceptor cells.
These results support the proposition that ey is the master control
gene for eye morphogenesis. Because homologous genes are
present in vertebrates, ascidians, insects, cephalopods, and
nemerteans, ey may function as a master control gene throughout
the metazoa." (Halder G., Callaerts P., & Gehring W.J., "Induction
of Ectopic Eyes by Targeted Expression of the eyeless Gene in
Drosophila", Science, Vol. 267, 1988, p1788)

This Pax-6 "`master control gene' for eye development ... sits at the top of
the network of genes, estimated at more than 2,000, used to form eyes":

"Several years ago, Walter J. Gehring of the University of Basel in
Switzerland was working on a zoology textbook. When it came
time to write a section that dealt with the evolution of eyes,
Gehring unhesitatingly recited the traditional view that eyes had
evolved independently dozens of times. For the next edition, he'll
pen a different scenario. The discovery of a gene shared by fruit
flies, mice, squid, and humans and the creation of unusual fruit flies
that sprout eyelike structures in places such as wings, legs, and
antennae have persuaded Gehring that all modern animals with eyes
evolved from a common ancestor that possessed a primitive image-
forming organ.... In essence, he contends that the eye probably
evolved just once in life's evolutionary history -- an assertion not
everyone is willing to accept. The eye has always been a thought-
provoking organ in discussions of evolution. Creationists have
regularly pointed to it as something so complex and specialized that
it could not have developed on its own. Charles Darwin also
considered eyes a formidable challenge to his theory of natural
selection. "To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different distances, for
admitting different amounts of light, and for the correction of
spherical and chromatic aberration, could have been formed by
natural selection, seems, I freely confess, absurd in the highest
possible degree," he wrote in On the Origin of Species. Yet Darwin
quickly dismissed this concern, arguing that the complex eyes of
modern animals could have evolved slowly from light-sensitive
nerve cells and not much else. In more recent years, evolutionary
biologists have been asking a different question: How often can
such an organ develop from scratch? While many creatures have an
ability to sense light, a survey of the animal world shows that a
minority of the major animal groups, or phyla, have true eyes. ...
While image-forming eyes are commonplace, no one design for
eyes dominates. Scientists have described almost a dozen distinct
blueprints, from the alien-seeming compound eyes of insects and
many other species to the cameralike single eyes of vertebrates like
us. The exotic appearance of the compound insect eye, with its
hundreds of miniature eyes called ommatidia, helps explain why
scientists have assumed that it evolved independently of the
vertebrate eye. Even superficially similar eyes provide evidence of
independent evolution. At first glance, the eyes of cephalopods such
as squid and octopuses closely resemble those of vertebrates. A
closer examination reveals that the organs emerge from different
embryonic tissues and differ considerably in the fine details of their
construction. Consequently, the two groups of eyes have been
thought a classic example of convergent evolution. ... Indeed, the
majority of scientists studying eye evolution ultimately decided that
the wide variety of eyes spread across the animal kingdom is
evidence that the organ could not have developed just once. In
1977, L. Von Salvini-Plawen and Ernst Mayr, both of Harvard
University, placed this conventional wisdom solidly on the record
when they published a landmark paper concluding that eyes had
arisen independently at least several dozen times. That's where the
story of eye evolution stood until 1993. That year, Gehring and
Rebecca Quiring, also of the University of Basel, were studying
fruit flies and looking for transcription factors -- proteins that
regulate the activity of genes. ... the researchers sent information on
the discovery of this protein and its gene to a worldwide computer
database to see if any similar genes, or homologues, had already
been reported. The database search highlighted two genes, one
from mice that is called Pax-6 (or small eye) and one from people
that is called Aniridia. Both genes, which are nearly identical to the
fruit fly gene, encode proteins crucial to eye development. ...
Gehring was surprised that the fly gene was so similar to the two
vertebrate genes, but the real astonishment came when he realized
that the insect gene also plays a role in eye development.... The new
gene, named eyeless, turned out to be more than just a cog in the
genetic machinery that makes a compound eye. When eyeless was
turned on in parts of the developing fruit fly where it is normally
inactive, it could sometimes initiate the development of additional
eyes in odd places. Even more remarkable, Pax-6 and Aniridia did
the same. Gehring's group added to fruit flies copies of the
vertebrate genes that had been engineered to become active in
imaginal disks, embryonic tissues that give rise to adult insect
structures like wings and legs. ... Moreover, the squid gene, like the
vertebrate genes, initiated formation of extra eyes when activated in
developing fruit flies. ... Gehring likes to call eyeless a "master
control gene" for eye development, one that sits at the top of the
network of genes, estimated at more than 2,000, used to form eyes.
"It's like the main electrical switch in a building. You turn on the
main switch and all the lights can go on," explains Gehring. ... Even
more controversial than Gehring's calling eyeless the master control
gene for eye development is his belief that its discovery in several
disparate species shatters the dogma that eyes evolved
independently on many occasions. "We now think that this event
happened only once," asserts Gehring. ... As for Gehring, he's
already confident enough in his interpretation that eyes probably
developed just once that he has begun to plan how he should revise
his textbook's section on eye evolution. "It's nice to disprove your
own text, as long as it doesn't happen too many times," he laughs."
(Travis J., "Eye-opening Gene: How many times did eyes arise?"
Science News, May 10, 1997.
http://www.sciencenews.org/sn_arc97/5_10_97/bob1.htm)

So how did that master gene which coded for all eyes, arise before it was
needed (but where and when it *had* to arise to give proper eyes to
everything downstream):

"I am in agreement with Mr. Gross when he refers to "new and
astonishing evidence" about the origin of the eye. Herewith the
facts. Halder, Callaerts, and Gehring's research group in
Switzerland discovered that the ey gene in Drosophila is virtually
identical to the genes controlling the development of the eye in
mice and men. The doctrine of convergent evolution, long a
Darwinian staple, may now be observed receding into the darkness.
The same group's more recent paper, "Induction of Ectopic Eyes by
Targeted Expression of the Eyeless Gene in Drosophila" (Science
267, 1988) is among the most remarkable in the history of biology,
demonstrating as it does that the ey gene is related closely to the
equivalent eye gene in Sea squirts (Ascidians), Cephalopods, and
Nemerteans. This strongly suggests (the inference is almost
irresistible) that ey function is universal (universal!) among
multicellular organisms, the basic design of the eye having been
their common property for over a half-billion years. The ey gene
clearly is a master control mechanism, one capable of giving general
instructions to very different organisms. No one in possession of
these facts can imagine that they support the Darwinian theory.
How could the mechanism of random variation and natural
selection have produced an instrument capable of anticipating the
course of morphological development and controlling its expression
in widely different organisms?" (Berlinski D., "Denying Darwin:
David Berlinski and Critics", Commentary, September 1996,
pp28,30.
http://www.commentarymagazine.com/9609/letters.html#CDD)

[continued]

Steve

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"Biology is the study of complicated things that give the appearance of
having been designed for a purpose." (Dawkins R., "The Blind
Watchmaker," [1986], Penguin: London, 1991, reprint, p.1)
Stephen E. Jones | Ph. +61 8 9448 7439 | http://www.iinet.net.au/~sejones
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