I admit to shortness of temper on this topic of suboptimality.
Alas, Mike and I drift further apart with each post.
First, retinal design. Mike writes:
>Goldsmith points out that that placing the retina before the
>photoreceptors is like "placing a thin diffusing screen directly over
>the film in your camera; it can only degrade the quality of the
>image."
Yes, that would be the case -- for a camera. But the vertebrate
eye is not a camera. It's an eye, which must continually maintain
its photoreceptors, recycle photopigments, and remove spent outer
segments of the photoreceptors. These tasks are accomplished by
the retinal pigment epithelium (RPE), which inter-fingers with the
photoreceptors at their "business end."
+
+++++++
+++++++
(to >>>>>>>>>>>>>>> +
optic <---- photoreceptor >> + retinal pigment epithelium
nerve) >>>>>>>>>>>>>>> + (RPE)
++++++++
++++++++
+
+
path of incoming light --->
Indeed, image quality is *known* to be affected by RPE disfunction
(Zinn and Marmor 1979). I know of no defects associated with
photoreceptor orientation, other than the completely hypothetical
ones spun from gossamer by Goldsmith (1990). I read Goldsmith
carefully, when that paper was first published, and he never even
attempts to demonstrate that the orientation is suboptimal. He
merely asserts it.
The problem with comparing the vertebrate to the cephalopod
system is the degrees of freedom involved. If one makes a list of
the features peculiar to each, it becomes immediately apparent that
one cannot isolate photoreceptor orientation as the only consideration
relevant to optimality. But that's just what Goldsmith does.
Mike writes:
>It is still not clear to me what advantages this arrangement
>has which outweigh the disadvantages. Neural processing in the
>retinal could take place with either arrangement so this does not
>seem to me to be a counter argument.
How do you know that neural processing could take place with either
arrangement? By observation?
No. By sheerest conjecture -- by inventing a hypothetical vertebrate
retina, and asking us to accept, entirely on your authority, that
this retina would function better than existing retinas.
On the issue of the recurrent laryngeal nerve, Mike writes:
>There is no KNOWN functional reason for a long pathway. Could there
>be a functional reason for the long pathway? Sure. Anything is
>possible - especially in biology. All we can do is to discuss the
>available evidence. You have to provide evidence of a function
>otherwise you could be accused of doing the armchair theorizing of
>which you accuse others.
Hey, you brought it up, and accused God of blundering. The burden of
proof rests with you, Mike. Show us that it's suboptimal. Don't
ASSERT it -- give us some *evidence*.
The following doesn't qualify:
>Biologists do have an explanation for the recurrent nerve.
>It was originally the 4th branch of the vagus nerve in the fish. Here
>the route is direct. The nerve followed the same route through the
>higher vertebrates but as the neck became longer the detour came to
>look increasingly absurd.
I'd be interested in this explanation if Mike could explain some
of the macroevolutionary transitions involved (e.g., the invention,
de novo, of the amniotic egg). But it's a tad silly to justify evolution
on the grounds of "you know, if I were the Creator, I'd make sure the
recurrent laryngeal nerve was shorter. Because God, as played by me,
wouldn't have done it that way. Thus the vertebrates must have
evolved."
Mike's other examples of suboptimality are also non-starters. The famous
"chick teeth" experiment (Kollar and Fisher 1980) was never cleanly
replicated, and doubts have been raised about the methods employed
(Marshall, Raff, and Raff 1994:12286-87; Raff 1996: 393). That some
cetaceans develop and resorb teeth in utero may be counterintuitive,
but I expect the structures play a developmental (inductive) role, and
in any case the argument is yet another variant of "if I were God I
wouldn't have done it that way." Its evidential force goes no further
than the theological premise.
About the panda's thumb. I searched the primary literature, thoroughly.
Members of this list are welcome to look, but I can tell you what you'll
find. Zip. The only evidence for the suboptimality of the giant panda's
pseudothumb is a claim made by Stephen Gould (1980), on his aesthetics.
I repeat my conclusion of yesterday. These arguments for evolution do
not deserve to be called science.
Paul Nelson
Goldsmith, T.H. 1990. Optimization, Constraint, and History in
the Evolution of Eyes. Quart. Rev. Biol. 65:281-322.
Gould, S.J. 1980. The Panda's Thumb. New York: W.W. Norton.
Kollar, E. and Fisher, C. 1980. Tooth induction in chick epithelium:
Expression of quiescent genes for enamel synthesis. Science 207:993-95.
Marshall, C., R. Raff, and E. Raff. 1994. Dollo's law and the death and
resurrection of genes. Proc. Natl. Acad. Sci. 91:12283-87.
Raff, R. 1996. The Shape of Life. Chicago: University of Chicago Press.
Zinn, K.M. and Marmor, M.F. 1979. The Retinal Pigment Epithelium.
Cambridge: Harvard Univ. Press.