Let me begin with a more conciliatory note. There is a lot in Paul's
postings (and Brian Harper's) with which I agree. I agree that it is
much easier to evaluate the optimality of simple systems than larger
ones. In suggesting that there are imperfections in living things I
am not arguing that God could have created a better world than the
one we have, I'm merely arguing that imperfections recall an
evolutionary past. An evolving universe with all its imperfections
could still be an optimal one.
MLA
> >Paul Nelson wants to know how it is that cephalapod retinas are
> >superior to vertebrate one's. I wouldn't put it this strongly. They
> >are superior in certain repects e.g. in not having a blind-spot.
PN>
> But this is precisely what needs to be demonstrated, namely, that
> having a blind spot, for vertebrates, is suboptimal to not having one.
> I agree that blind spots seem counterintuitive. Much of
> biology is counterintuitive until one looks more deeply. Turning
> around vertebrate photoreceptors, so that their "wiring" runs
> out the back -- thus eliminating the blind spot -- doesn't appear to
> be the simple design fix many evolutionary biologists claim.
> Brian Harper has already mentioned the critical role of the retinal
> pigment epithelium, which interlaces with the photoreceptors.
> Indeed, a fair amount of signal processing occurs in vertebrate
> photoreceptors, even before the nerve signal reaches the main
> trunk of the optic nerve. The wiring of the cephalopod retina,
> on the other hand, is entirely different -- most signal processing
> appears to occur in the optic lobe, some distance from the
> eye itself.
>
> Thus it's far from obvious how properly to assess relative
> optimality in these systems. What bothers me about suboptimality
> claims is how facile they are. Few people even bother to show
> the steps in their reasoning, or to demonstrate a rigorous path for
> assessing suboptimality, in this, or most other systems for which
> suboptimality is claimed. Most of the time people just wave their
> hands and say, gee, I wouldn't have done it that way.
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." 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.
>
> Mike also asked me to respond to the following:
>
> >A better subject [to illustrate suboptimality] is nerve pathways.
> >It is very curious that the recurrent laryngeal nerve should pass
> >from the brain, down to the heart and back up to the larynx.
> >What adaptive advantage could there be to such a roundabout
> >route? It is easy to come up with a better design. Send the nerve
> >straight to the larynx. The actual pattern is easy to understand
> >as an accident of history as fish evolved into the higher vertebrates.
> >Standard comparative morphology texts tell the story.
>
> Ken Miller of Brown University used this very example in his
> debate with Mike Behe and me at the ASA meeting in 1995. He
> had a beautiful slide, actually, of the neck of the giraffe, where
> the recurrent laryngeal nerve makes a truly long trip, down down
> down, and then back up again to the larynx.
>
> "It is easy," Mike writes, "to come up with a better design.
> Send the nerve straight to the larynx."
>
> How is that better? I mean, better, not in one's imagination --
> armchair re-design is easy, right? -- but in fact. When Miller
> made this claim, I asked him how he knew there was no
> functional reason for the long pathway. And, bless him for
> his honesty, he admitted he didn't know.
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. Worse, you could be accused of a fallacy
(hypothesis contrary to fact) or of doing less than dignified
science. 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.
If these examples don't work for you, perhaps others would. Certain
cetaceans produce teeth during development which are then reabsorbed
before birth. I find it hard to find a function for the teeth since
the foetus gets its its nourishment via the placenta. Chickens have
genes for teeth. It isn't easy to see a function for a gene which is
never expressed. I haven't checked out the panda example. If anyone
could provide references I would be grateful. Gould is a popular writer -
no discredit to him intended. I'm looking for literature from
morphologists.
Mike
>
________________________________________________
Mike L Anderson, PhD
Director: Christian Academic Network
mla@iafrica.com
78 Balfour Road, Rondebosch, 7700