On Fri, 19 Apr 96 00:16:06 GMT you wrote:
[continued]
AM>It is also important to realize that even with misaligned
>crystallographic axes, a lens composed of calcite would *not* be useless
>(contrary to the claims of some of your quotes), just not as effective as
>it could be.
I cannot recall any of my quotes claimed that a misaligned calcite eye
would be "useless". I would not claim this myself, but I would claim
that the *whole system* must be substantially in place before even a
partial eye can be useful:
"The first step towards a new function-such as vision or ability to
fly-would not necessarily provide any advantage unless the other parts
required for the function appeared at the same time. As an analogy,
imagine a medieval alchemist producing by chance a silcon microchip;
in the absence of a supporting computer technology the prodigious
invention would be useless and he would throw it away. Stephen Jay
Gould asked himself "the excellent question, What good is 5 per cent
of an eye?," and speculated that the first eye parts might have been
useful for something other than sight. Richard Dawkins responded
that:
`An ancient animal with 5 per cent of an eye might indeed have used it
for something other than sight, but it seems to me as likely that it
used it for 5 per cent vision. And actually I don't think it is an
excellent question. Vision that is 5 per cent as good as yours or
mine is very much worth having in comparison with no vision at all.
So is 1 per cent vision better than total blindness. And 6 per cent
is better than 5, 7 per cent better than 6, and so on up the gradual,
continuous series.'
The fallacy in that argument is that "5 per cent of an eye" is not the
same thing as "5 per cent of normal vision." For an animal to have
any useful vision at all, many complex parts must be working together.
Even a complete eye is useless unless it belongs to a creature with
the mental and neural capacity to make use of the information by
doing something that furthers survival or reproduction."
(Johnson P.E., "Darwin on Trial", InterVarsity Press: Downers Grove
Ill., Second Edition, 1993, p34)
But is there any evidence that any of the early trilobite's eyes
*were* "misaligned"?
SJ>To do this, a two-part
>lens is needed which has a waved surface at the junction between its
>two elements. And this is exactly what these trilobites have
>developed. The lower element of the double lens was formed by chitin
>and the surface between the two conforms to a mathematical principle
>that man discovered only three hundred years ago when trying to
>correct the spherical aberration of lenses in his telescopes."
>(Attenborough D., "Life on Earth: A Natural History", Collins-British
>Broadcasting Corporation: London, 1979, p54),
AM>I am not denying that these amazing corrective optics were present
>in trilobites, only that they were *not* present at the start. They occur
>later. The "doublet" structure is not known in the earliest trilobites.
>I suppose it is possible they were down there (the record for Cambrian
>trilobite eyes is not great because of the way the skeleton was shed by
>many at that time), but there is no sign of them.
OK. But is there any evidence for a trilobites holochroal eye
transforming step-by-step into a "schizochroal eye? If not it must
be assumed by evolutionists that the latter did originate in the
"Cambrian".
>AM>They do not occur until the Ordovician, considerably after the
>initial occurrence of trilobites near the base of the Cambrian. The
>earliest trilobites had holochroal eyes
SJ>Raup, speaking particularly of later trilobite eyes, says they were
>"nearly identical to designs published independently by Descartes and
>Huygens in the seventeenth century" and "used an optimal design which
>would require a well trained and imaginative optical engineer to
>develop today":
AM>Yes. The later schizochroal eyes.
Yes. That's what I said: "speaking particularly of later trilobite
eyes"! :-) That's still amazing, is it not? How did a blind
watchmaker achieve "an optimal design which his require a well trained
and imaginative optical engineer to develop today" by a trial and
error random search, and where is the evidence of the trials?
[....]
SJ>"[T]he lens systems were very different from what we now have.
>Riccardo Levi-Setti (a Field Museum research associate in geology and
>professor of physics at the University of Chicago) has recently done
>some spectacular work on the optics of these lens systems. Figure 7
>....
>
>trilobites lived, the lower lens was necessary. Thus, the trilobites
>450 million years ago used an optimal design which would require a
>well trained and imaginative optical engineer to develop today-or one
AM>I highly recommend Levi-Setti and Clarkson's papers (cited in my
>first comment). They provide far more detail than I could ever
>communicate here. The point I tried to make is not that schizochroal eyes
>are "simple". They are impressive. I was trying to make the point that
>they did not appear at the point trilobites first appeared. The "450
>million year" time frame mentioned in this quote refers to the Ordovician,
>when schizochroal eyes are first known, not the Cambrian, when trilobites
>are first known.
>
>The quote from Sunderland also says, while talking about the
>doublet structure, "... and it is bound into another layer that has to be
>just exactly right for them to see anything..." This is an exaggeration.
>For them to collect light and see *optimally*, this is correct, but if the
>arrangement were otherwise, they would still see. The eye would still
>function as a light detector at least. Not all features would have to be
>present at the same time in order for the eyes to be effective to some
>degree. In fact, this is empirically demonstrated by trilobite eyes
>without these features.
Agreed. YECs sometimes claim too much because they are trying to prove
that everything arose instantaneously. PC does not claim this.
>AM>Many trilobites were also blind. The visual system of
>trilobites is unusual because it stands a reasonable change of
>preservation. This is quite different from the preservation potential of
>eyes in most organisms. The difference in preservational potential
>occurs because the lenses consist of calcite -- CaCO3 -- the mineral
>which is the main ingredient of limestone. The lenses are also closely
>integrated with the rest of the skeleton in many trilobites.
SJ>Indeed, Taylor writes of this "calcite" eye:
>
>"Kenneth Towe of the Smithsonian Institute reported that the lenses in
>the eyes of fossil trilobites consisted of precisely aligned crystals
>of calcite.
AM>Aligned along the "c" optical axis to minimize (but not eliminate)
>the effect of birefringence and maximize the refractive index.
Thanks.
SJ>with the transparency of glass only if they are exactly aligned
>with the beam of light entering them. At any other angle, the light
>bounces off the walls and splits into various colours. Some modern
AM>This is a reference to the birefringence. It does not "split" the
>light into "various colours", but colours can be an effect when the rays
>emerge and interfere at the surface of the lens.
OK.
SJ>arthropods have calcite crystals in their eyes, but these- and Towe
>finds this 'an altogether surprising thing' - are arranged randomly,
>and do not correspond with the ommatidia or optical units of which the
>compound eye is composed.
AM>Incidentally, from what can be determined about holochroal
>trilobite eyes from the lenses, they appear to have had similar structure
>and function to the ommatidia of other "arthropods".
OK.
>By what mechanism did these 'primitive'
>creatures discover how to incorporate calcite crystals, align them
>precisely and protect them with a cornea? Answer comes there none."
>(Taylor G.R., "The Great Evolution Mystery", Abacus: London, 1983,
>p96)
AM>Hard to say. Alignment of crystallographic axes in calcite is
>common in other organisms for structural reasons, because one of the other
>problems with calcite is its three perfect cleavages -- i.e. it has 3
>orientations of parallel planes of weakness that are related to the
>crystal structure. For example, crinoids and other echinoderms, whose
>platey skeletons are composed of single crystals of calcite, do this. It
>is completely unrelated to optical alignment, but many organisms do have
>ways to align calcite crystal growth, mainly by establishing organic
>templates upon which the crystals can grow. I am not sure of the details,
>but if you look up the subject of biomineralization, you could probably
>find them. As to how trilobites aquired this ability specifically for
>optics, it is impossible to tell from the fossil record, just as it would
>be for determining crystal alignment in the rest of the skeleton without
>having the corresponding soft tissues.
OK. I do not rule out physical contraints (as Brian Goodwwin points
out in "How the Leopard Changed its Spots) as a factor in Intelligent
Design. An Intelligent Designer would be expected to use the physical
laws he had created.
AM>[reiteration of what is contained in the earlier quote, based upon
>Levi-Setti and Clarkson's work]
SJ>Thus the trilobites evolved a lens shaped to correct for optical
>aberration identical to that proposed (quite independently of any
>knowledge of trilobites) by Descartes and Huyghens half a billion
>years later.
>
>Why was such perfection needed? Dr Clarkson suggests that trilobites
>may have lived in very muddy, turbid water. Or perhaps they only came
>out at night or at dusk. The thick lenses, thanks to the optical
>correction, would be more efficient light-collectors.
AM>It is interesting that this develops later, as more and nastier
>predators start appearing (e.g., cephalopods).
OK. I have no problem with natural selection fine-tuning an
already present design.
SJ>But to make the
>matter more puzzling still there is the fact that some trilobites were
>blind. How did the earliest trilobites collect together the intricate
>genetic information needed to construct this semi-miraculous
>structure?"
>
>(Taylor G.R., "The Great Evolution Mystery", Abacus: London,
>1983, p96-97)
AM>Without at least skeletal remains going back much further, it is
>impossible to tell.
[...]
>AM>The first occurrence of trilobites is not as simple as a general
>>examination of the fossil record would indicate. There are many
>trace fossils (trails, burrows, etc.) of trilobite-like animals
>prior to the first occurrence of trilobite skeletal material. There
>are also examples of entirely soft-bodied trilobites and
>trilobite-like animals from localities with exceptional preservation
>(e.g., the Burgess Shale). These observations suggest the first
>appearance of common skeletal fossils of trilobites near the base of
>the Cambrian may be a taphonomic artifact of the development of
>mineralized skeletons rather than their actual time of origin. It is
>likely the exact origin of the oldest trilobite eyes will be unknown
>until soft-bodied preservation of at least Burgess Shale quality is
>found in even older rocks than is currently known (e.g., older than
>the Chenjiang fauna).
SJ>Whatever,
AM>"Whatever"? These issues are crucial. There is evidence that the
>first appearance of *skeletal* remains of trilobites does not represent
>their first appearance in any form. There are trace fossils and at least
>possibly-related, older, soft-bodied organisms. There are also limits on
>preservation because of size. The first trilobites found in the Cambrian
>are already quite small, and if earlier ones did not possess a skeleton
>(as evidenced by the trace fossils), their chances of preservation are
>nearly nil. The "poof" of creation could as easily be the "poof" of
>development of skeletons and a taphonomic artifact, at least in part. It
>is at least as plausible as the interpretation you have proposed, which
>depends upon the failure to find Burgess-Shale quality preservation
>further back into the Precambrian. If it turns up, what then?
I will then revise my model. I have never claimed the first
appearance of trilobites in the Cambrian as "`proof' of creation". I
am not a YEC so I do not need to prove instantaneous creation. A
*geologically* sudden appearance of phylla with an absence of
step-by-step transitional forms would be more consistent with a PC
model.
But equally, I note your "older soft-bodied organisms" are only "at
least possibly-related" and your "trace fossils" are "of uncertain
interpretation". All the evolutionist literature I have read admits
that the trilobites and other animal phylla originated in the Cambrian
explosion:
"Life remained almost exclusively unicellular for the first five
sixths of its history-from the first recorded fossils at 3.5 billion
years to the first well-documented multicellular animals less than 600
million years ago. (Some simple multicellular algae evolved more than
a billion years ago, but these organisms belong to the plant kingdom
and have no genealogical connection with animals.) This long period
of unicellular life does include, to be sure, the vitally important
transition from simple prokaryotic cells without organelles to
eukaryotic cells with nuclei, mitochondria and other complexities of
intracellular architecture-but no recorded attainment of multicellular
animal organization for a full three billion years...curiously, all
major stages in organizing animal life's multicellular architecture
then occurred in a short period beginning less than 600 million years
ago and ending by about 530 million-years ago-and the steps within
this sequence are also discontinuous and episodic, not gradually
accumulative." (Gould S.J., "The Evolution of Life on the Earth",
Scientific American, October 1994, p66).
and
"he subsequent main pulse, starting about 530 million years ago,
constitutes the famous Cambrian explosion, during which all but one
modern phylum of animal life made a first appearance in the fossil
record...The Bryozoa, a group of sessile and colonial marine
organisms, do not arise until the beginning of the subsequent,
Ordovician period, but this apparent delay may be an artifact of
failure to discover Cambrian representatives....Although interesting
and portentous events have occurred since, from the flowering of
dinosaurs to the origin of human consciousness, we do not exaggerate
greatly in stating that the subsequent history of animal life amounts
to little more than variations on anatomical themes established during
the Cambrian explosion within five million years." (Gould S.J., "The
Evolution of Life on the Earth", Scientific American, October 1994,
p67).
[continued]
Regards.
Steve
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