Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.1 6/24/83; site utastro.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!zehntel!hplabs!hao!seismo!ut-sally!utastro!bill From: bill@utastro.UUCP (William H. Jefferys) Newsgroups: net.origins Subject: Re: Integrated Circuits. Part II. Message-ID: <871@utastro.UUCP> Date: Tue, 4-Dec-84 10:50:53 EST Article-I.D.: utastro.871 Posted: Tue Dec 4 10:50:53 1984 Date-Received: Thu, 6-Dec-84 06:41:13 EST References: <502@uwmacc.UUCP> Organization: UTexas Astronomy Dept., Austin, Texas Lines: 197 At the end of a very long article, Paul DuBois says of my article: >Well, anyway. Bill referred to overall design, but mentioned only >the retina and the blind spot specifically. Perhaps he would like >to restate his case, so I will leave off here. Thank you, Paul. I wanted to concentrate only on these issues because I believe they can be treated in isolation from the multitude of other issues you raise. I had originally said: >> Pray tell, if we are at the pinnacle of Creation, >> how come the Creator got it right with the octopus and then stuck us >> with a second-rate design? From this, Paul derived what he thought was my position, to wit: >(b) if humans are the pinnacle of creation, there should be no > sensory function which a human performs more poorly than any > other created organism. (last sentence of second excerpt) This is not the same as the position I stated in my article, nor do I agree with it. For the record, let me stipulate that I recognize that a creator would take into account the needs of different organisms and design eyes which were appropriate to the ecological niche occupied by each organism. I am quite aware of the need for engineers to make design trade-offs. That is not an issue. Therefore, most of Paul's article (which counters point [b] above) is not relevant to my article. My point is rather simpler. The general design of the cephalopod (e.g., octopus) and vertebrate (e.g., human) eye is the same. The major structural difference is the design of the retina, which in the cephalopod may be said to be in "normal" position, and in the vertebrate in "inverted" position. All other things being equal, I claim that the cephalopod design is superior to the vertebrate design since the latter has a "blind spot". I can think of only a few ways to counter this simple observation. First, it may be claimed that God knows best, and we are not to question His decisions. I reject this. I hope that I am not misreading Paul's article, but it seems that he accepts this as a legitimate position. It is obvious to me that an argument of this kind has no place in science. Secondly it may be argued that the two designs are equally good, so that it doesn't matter which design is picked. Paul addresses this issue: >The contention is that the blind spot constitutes faulty design. >Does it? Perhaps. Let us examine the question. A blind spot is an >area of the retina from which no visual information may be received. >In the vertebrate eye this is a consequence of the fact that >photoreceptors are "backward". The receptors are oriented with the >photoactive part pointed toward the back of the eye, while the >ganglia to which they are (indirectly) connected pass their axons >out of the front of the retina. The axons all converge at a point >near the fovea (area of greatest acuity) and pass out together >through the rear of the ocular globe, forming the optic nerve. At >this point of convergence there are no photoreceptors, hence no >visual information about the portion of the visual field projecting >on that area. Hence the term blind spot. > >For an *actual* disability to result from this physiological >structure, the possessor of the eye must be: > >(i) Unable to move the eye (for otherwise a visually receptive > portion of the retina could be rotated to receive > information from the part of the visual field corresponding > to that projecting on the blind spot). >(ii) Unable to move the head (such movement would allow crude > approximation of eye movement). >(iii) Unable to move the body (ditto). >(iv) Monocular, because the blind spots of binocular organisms do > not correspond to the same part of the visual field. >Clearly, any sighted organism satisfying all of these criteria may >have more serious things to worry about than a lack of visual >capacity in a certain portion of its retinae.... >You see what I'm driving at. The blind spot may *seem* to be a >fault of design, but it simply is not important in a functional >sense. Ask your friends to find theirs. How many of them can do >it? Even those who can must engage in a certain amount of trial and >error to locate it. This suggests a minimal or nonexistent >incapacity. Certainly point (iv) above provides a partial >explanation of why this is so: One of many consequences of >binocularity is that the blind spot becomes pretty much irrelevant, >since the fields of vision subtended by the two eyes in the areas of >the blind spots do not overlap. > >The brain also, to a certain extent, compensates in curious ways >under conditions of monocular viewing. A checkerboard grid may be >modified by placing a small circular patch where four squares join. >When foveal retina is rotated under the image of the patch (i.e., >when you "look at it"), you see the patch, as might be expected. >But then the blind spot is rotated under the image, an unmodified >checkerboard is perceived: the patch disappears (assuming the >visual angle of the patch is less than that subtended by the blind >spot, of course). The brain seems to generate a hypothesis about >what "ought" to be seen. The regular pattern of the checkboard >allows an obvious inference as to the nature of that hypothesis, >which in the above case is incorrect. Who know why this should >occur? Why should we just not perceive a hole in the visual field? >I don't know. It certainly seems an odd thing for a creator to >build in; it seems extraordinary that it should arise through >evolutionary processes. I would say that these points argue for *evolution*, not creation. Paul has shown how "kludging around" with other aspects of the human visual system are able to compensate for the design flaw, which is precisely the point I made more generally. Paul mentioned a third argument that I had not thought of, namely, that the human eye perhaps had degenerated from an originally more perfect design: >If a more positive statement were desirable, one might infer a >principle of genetic deterioration in consonance with the tenet of >physical degeneration that seems to be a part of the standard >creationist model, citing as specific evidence the deleterious or >lethal nature of many mutations. (To be sure, without a more >specific formulation, one immediately runs into problems. For >example, *when* should we expect to find genetic disintegration, and >*why* should we expect to find it *then* and not otherwise? Under >what specific conditions ought it to occur? This is one analogue of >a difficulty in evolutionary theory, viz., stasis: *when* will an >organism undergo change and *why*? Under what specific conditions >will an organism stay the same for millions of years, while others >do not?) I find this an amazing hypothesis to come from a Creationist. To go *from* a normal cephalopod retina *to* an inverted vertebrate one would seem to be much more difficult than evolving either from simpler forms, yet Creationists are always saying that even the latter kind of transition is impossible. It should be pointed out that for this hypothesis ("degeneration from a normal to an inverted retina") to hold water, one would have to explain why it happened universally to all the vertebrates and to none of the cephalopods. If the cephalopod design were original, at least some of the vertebrates ought to have retained it. Finally, it may be argued that there is a genuine design trade-off. That is, perhaps there is something about the inverted retina that makes an important trait such as color vision possible. Paul also alludes to this: >Bill has discussed one aspect of visual function (ther retinal blind >spot), concluding that the evidence implies inferiority of the human >eye. My comments in the previous section lead to a different >conclusion, but I still have to ask in a more general sense how the >human eye is "clearly inferior" to the octopus eye. Bill mentions >the overall design ("design" being a poor word given the thrust of >his argument), but his comments only discussed the design of the >retina. This is certainly artificial; a retina is useless by >itself. Let us consider general ocular superiority. This would >include consideration of such things as the following: > > o accommodative ability > o chromatic and spherical aberration of the lens > o pupillary reflex > o vergence and version control for binocular functioning > o stereopsis > o resolution of extraocular muscle nervous innervation > o night/day visual capacity, pattern of neural convergence > of the photoreceptors onto the ganglia (already discussed) > o color vision > o rod/cone demography > o response to foreign objects (i.e., defense against) > o facilities for distance perception Of this list, only color vision and rod/cone demography, which involve the retina, might be endangered by a different retinal design. The other aspects could equally well exist in conjunction with either the cephalopod or the vertebrate design. To make a case for a design trade-off requiring an inverted retina, one would have to provide evidence to show that a normal retina cannot support these aspects of human sight. No such case has been made, and I would argue that it is unlikely that any such case can be made. >I find it curious that evolutionists continually raise the point >about our inability to predict, *a priori*, any limits on the way in >which a creator would create - and then go ahead and make their own >suppositions. On the contrary, whenever an obvious "prediction" is pointed out that is not observed in fact, Creationists can think of a "reason" why the "prediction" should be ignored. It is Creationism that is malleable in this regard, not evolution. -- "When evolution is outlawed, only outlaws will evolve" Bill Jefferys 8-% Astronomy Dept, University of Texas, Austin TX 78712 (USnail) {allegra,ihnp4}!{ut-sally,noao}!utastro!bill (uucp) bill%utastro.UTEXAS@ut-sally.ARPA (ARPANET)