We are all familiar with the creationist argument about the eye, an argument which Darwin already addressed in his original work. And while creationists are still in much of a denial about eye evolution, science keeps on closing gaps.
In the Australian a second paper addressing eye evolution is discussed.
A SECOND publication this week by Australian National University scientists on the evolution of the eye has rebuffed intelligent design proponents who argue that such a complex organ could not have been arrived at gradually. Paleobiologist Gavin Young discovered in a 400-million-year-old exposed former tropical reef that a fossil of a placoderm, a bone-covered predator fish, had eye casings that showed a transitional arrangement of muscles and nerves.
Earlier, ANU Centre of Excellence in Vision Science head Trevor Lamb published a paper that called the deep-sea hagfish, with primitive photoreceptors for eyes, the missing link in the evolution of the organ of sight.
Dr Young’s placoderm and its visible muscle and nerve canals were evidence of an intermediate stage between jawless and jawed vertebrates, he said.
“It is transitional … in that it is the only example among all living jawed species and all extinct jawed vertebrates where we have the combination of jaws plus a primitive eye muscle arrangement.”
The eyeball was connected to the braincase by cartilage, as in modern sharks, and there was a primitive eye muscle arrangement as in living jawless fish.
Dr Young said that arrangement was different from all modern vertebrates, in which there is a consistent pattern of tiny muscles for rotating each eyeball.
Creationists and proponents of intelligent design argue that knowledge of evolution is gleaned from living creatures and that there is no historical evidence of evolution.
So while science is advancing at a quick pace, some Intelligent Design proponents are still stuck in last decade, wonder where do eyes come from.
Compare the output of science with the output of Intelligent Design as it applies to our understanding of the evolution of the eye and ask yourself a simple question: How does ID explain the eye? The answer or lack thereof may shock you and yet that is the full extent of ID’s contribution to science. Nothing.
The paper by Young can be found here, titled “ Number and arrangement of extraocular muscles in primitive gnathostomes: evidence from extinct placoderm fishes”
Abstract : Exceptional braincase preservation in some Devonian placoderm fishes permits interpretation of muscles and cranial nerves controlling eye movement. Placoderms are the only jawed vertebrates with anterior/posterior obliques as in the jawless lamprey, but with the same function as the superior/inferior obliques of other gnathostomes. Evidence of up to seven extraocular muscles suggests that this may be the primitive number for jawed vertebrates. Two muscles innervated by cranial nerve 6 suggest homologies with lampreys and tetrapods. If the extra muscle acquired by gnathostomes was the internal rectus, Devonian fossils show that it had a similar insertion above and behind the eyestalk in both placoderms and basal osteichthyans.
As a reminder, Darwin’s comments, which are often presented out of context to suggest that evolution cannot explain the eye, read as follows
To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. (Darwin 1872)
Yet reason tells me, that if numerous gradations from a perfect and complex eye to one very imperfect and simple, each grade being useful to its possessor, can be shown to exist; if further, the eye does vary ever so slightly, and the variations be inherited, which is certainly the case; and if any variation or modification in the organ be ever useful to an animal under changing conditions of life, then the difficulty of believing that a perfect and complex eye could be formed by natural selection, though insuperable by our imagination, can hardly be considered real. How a nerve comes to be sensitive to light, hardly concerns us more than how life itself first originated; but I may remark that several facts make me suspect that any sensitive nerve may be rendered sensitive to light, and likewise to those coarser vibrations of the air which produce sound. (Darwin 1872, 143-144)
Darwin continues with three more pages describing a sequence of plausible intermediate stages between eyelessness and human eyes, giving examples from existing organisms to show that the intermediates are viable.
Source: Index to Creationist Claims: Claim CA113.1: Charles Darwin acknowledged the inadequacy of evolution
Not surprisingly, science has been slowly uncovering the pathways of eye evolution and found that contrary to creationist beliefs, natural pathways seem to exist. No wonder that some creationists are still stuck in last decade as scientific knowledge has closed many of the gaps that existed then.
I hope to discuss this paper and the Nature paper on eye evolution in an upcoming posting as they show how science goes about closing gaps of ignorance and how ID stands by unable to contribute much of anything other than pointing out that there are still gaps remaining.