Re: Mammalian eyes...

Mike L Anderson (mla@mickey.iafrica.com)
Mon, 11 Nov 1996 11:21:44 +0000

Brian Harper wrote
> This type of observation is very common and I think also very
> naive from the standpoint of design. Paul Nelson has written
> a really great article about the argument from imperfection
> that I suggest everyone should read. I understand it has now
> been published, so if Paul is listening maybe he could give
> us the reference.
>
> The reason I say the above is naive is that it assumes one
> can change one aspect of a design keeping everything else
> the same. This might be possible with simple designs but
> almost certainly is not for complicated ones. I did a lot of
> reading on eyes awhile back and from what I read it seemed
> to me (a non-expert on eyes) that the at first seemingly
> irrational arrangement alluded to above actually allows
> the pigment epithelium (I hope I'm remembering this
> correctly) to perform several different functions that it
> otherwise would be unable to perform. One might then
> argue that any loss in image quality is offset by the improved
> efficiency of having one component perform multiple functions.
> Besides, the deleterious effects of the actual arrangement are
> very slight.
>
My reading tells me that the apparently irrational arrangement of
the vertebrate is the result of embryological constraint rather
than adaptation. The vertebrate eye develops by an invagination
of the optic vessicle. The front wall develops into the retina,
while the back wall becomes the pigment epithelium.

> Now, one might counter the above by saying that God is not
> constrained in the way human engineers are and that He
> could optimize all aspects of a design simultaneously without
> having to do trade-offs such as that above.

I would think that God is not constrained by ontogeny.

> On the other hand, if the conversation begins with the evolutionist
> saying "look, this design is imperfect, it couldn't be designed"
> then the counter is not legit since it introduces a theological
> question regarding what God would or wouldn't do. The evolutionist
> has made the charge that the design is not perfect, the onus is on
> him to prove it by finding a better design without appealing to
> theological arguments.

Why could I not argue as a theistic evolutionist?

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.

Nick asks the question whether the eye is like the U.S. government
reflecting the cotingencies of history. Goldsmith has written an
excellent review article on the evolution of eyes in the Quarterly
Review of Biology Vol 65 No. 3 (1990) in which he shows just this
albeit to a limited extent. Eyes are perhaps not the best subjects for
elucidating evolutionary history because they are often so critical
for the functioning of an organism. There are impressive
examples of optimization even in invertebrate eyes.

A better subject 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.

I would be interested to see Paul Nelson's response to this example.

Does anyone know whether the contigencies of history have been
documented in the development of roads? It would make a nice
illustration.

Mike
________________________________________________
Mike L Anderson, PhD
Director: Christian Academic Network
mla@iafrica.com
78 Balfour Road, Rondebosch, 7700