I am plucking out only one issue. I hope this is okay.
[speaking of evolutionary hypotheses about the origin of eyes,
specifically refering to Dawkin's statements]
Stephen Jones wrote:
|Indeed, the trilobite, one of the earliest animals, had a highly
|developed eye:
The type of eye being discussed is called a schizochroal eye.
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, which were not as sophisticated in terms
of optics. 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. Most eyes in other organisms
are mainly organic material with lower preservation potential (there are
exceptions, though). You can see some examples of schizochroal trilobite
eyes at:
http://www.geo.ucalgary.ca/~macrae/trilobite/trilobite.html
The _Phacops_ has the best examples.
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). For more discussion about the early history of
trilobites, I recommend:
http://www.rt66.com/diamond/trilobites.html
Which is an article by Rob McNaughton containing plenty of
references.
|"One example of this is the little animal called the trilobite. There
|are a great many fossils of the trilobite right there at the beginning
|with no build-up to it. And, if you examine them closely, you will
|find that they are not simple animals. They are small, but they have
|an eye that has been discussed a great deal in recent years-an eye
|that is simply incredible. It is made up of dozens of little tubes
|which are all at slightly different angles so that it covers the
|entire field of vision, with a different tube pointing at each spot on
|the horizon. But these tubes are all more complicated than that, by
|far. They have a lens on them that is optically arranged in a very
|complicated way, and it is bound into another layer that has to be
|just exactly right for them to see anything...
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
This is probably a reference to the problems which result from
using a mineral like calcite for optics. It is highly anisotropic.
Refraction effects are severe in calcite unless the crystals are suitably
oriented and compensated for. This may be why so many other animals use
less anisotropic or more versitile organic materials for lenses. It is a
relatively simple material for many organisms to produce, but can be
pretty problematic to use.
|But the more complicated it is, the
|less likely it is simply to have grown up out
|of nothing. And this situation has troubled everybody from the
|beginning-to have everything at the very opening of the drama. The
|curtain goes up and you have the players on the stage already,
|entirely in modern costumes.
This is an exaggeration. Cambrian trilobites had simpler eyes.
They were only "half clothed" or dressed in "19th century" vintage attire.
Trilobites of the Cambrian are sophisticated creatures, but lack many
features found in later trilobites. To a first approximation, what
Sunderland is saying is correct, but it is an oversimplification.
|The creationists say, 'That is abrupt
|appearance,' and they hammer away at that. Instead of building up bit
|by bit, it appears suddenly, and that to them signifies creation. I
|don't want to argue that, but I admit it is very strange that there is
|no slow build-up. The evolutionists have strained very hard to find
|earlier fossils and have had very meager results" (Sunderland L.D.,
|"Darwin's Enigma: Fossils and Other Problems", Master Book
|Publishers: El Cajon, CA, Revised Edition, 1988, p150-151)
There are earlier fossils, but they are both interesting and
frustrating, because the preservation is not, in general, good enough to
resolve what many of the creatures making trails and burrows were, and not
good enough to preserve relatively small organisms (say, in the range of
typical invertebrate larvae today). More than what is preserved/known as
body fossils was present, judging by the burrows and trails. There are
also some fossils which might be trilobite ancestors, but they are not
well enough preserved to recognize eye details. Most of the soft-bodied
preservation so far found in Precambrian rocks is just not detailed
enough.
For more information on trilobite eyes, I recommend the following
popular and more technical literature:
Levi-Setti, 1993. Trilobites, Second Edition. The University of Chicago
Press: Chicago, p.1-342. ISBN 0-226-47451-8.
Clarkson, E.N.K., 1973. Morphology and evolution of the eye in Upper
Cambrian Olenidae (Trilobita). Palaeontology, v.16, part 4, p.735-763.
Clarkson, E.N.K., 1979. The visual system of trilobites. Palaeontology,
v.22, part 1, p.1-22.
Zhang Xi-Guang and Clarkson, E.N.K., 1990. The eyes of Lower Cambrian
eodiscid trilobites. Palaeontology, v.33, part 4, p.911-932.
Unfortunately, there is more to eyes than just the lenses, and
compared to the large number of trilobites known, the eyes of relatively
few have been examined in detail.
-Andrew
macrae@geo.ucalgary.ca
home page: http://www.geo.ucalgary.ca/~macrae