Hagfishing for Eye Evolution

first_imgDarwin recognized the vertebrate eye as one of the biggest challenges for his theory.  Still in 2008, evolutionists are debating it.  Two recent articles, both pro-evolution, reveal almost black-and-white attitudes about the problem.  One is cheery and optimistic; the other sober.    Eye evolution?  No problem.  That seems to be the view of Kate McDonald, who wrote “Slimeballs and eyeballs: hagfish and the evolution of the eye” for the Australian Life Scientist.  She thinks recent attempts in putting the parts together have forced creationists to blink.  She quoted Darwin’s famous worry as a fulcrum to spring back against critics:Charles Darwin famously highlighted the eye, “with all its inimitable contrivances”, as one of the hurdles in the acceptance of his theory of natural selection.  “[It} seems, I freely confess, absurd in the highest possible degree”, that this complex organ arose as the result of natural selection.  This confession has in the past been seized upon by the bright lights of the intelligent design movement and their ilk as proof that Darwin himself had doubts about his own theories.    Creationists have gone a bit quiet on this front in recent years as more is known about the evolution of the eye, and they might just be done away with completely if a hypothesis set out in a Nature Reviews Neuroscience paper last December proves to be correct.A hypothesis is not a proof.  One looks in vain in Ms. McDonald’s five-page treatise for evidence that the team of Trevor Lamb, Shaun Collin and Ed Pugh have pulled off an upset in this long-standing contest.  All they have proposed is a five-stage pathway animals might have traversed from simple light-sensitive spots to the vertebrate retina with its focusing lens and optic nerve.  This all assumes the eye evolved in the first place.  By the end of the article, it becomes apparent that they have only suggested a path for further investigation.  Their solution lies in future tense.    A key player on their proposed evolutionary path is the hagfish – a slimy jawless eel, which McDonald spends time telling us is as ugly as its name.  Both hagfish and lampreys belong to Agnatha, a group of marine jawless fish thought to have arisen 530 million years ago.  While hagfish have simple “proto-eyes,” their cousins the lampreys have the whole shebang.  Lamb, Collin and Pugh have to cram a lot of innovation into the next period:Then comes stage four, a period of about 30 million years, in which lamprey-like ancestors evolve and photoreceptors with cone-like features appear, along with an explosion in visual ability.  Genome duplications give rise to multiple copies of the phototransduction genes, which allow light to be converted into electrical signals; cell classes diverge into five cone-like receptors; cone bipolar cells and ganglion cells evolve; ganglion-cell axons project into the thalamus and the optic equipment evolves – the lens, the iris and the extra-ocular muscles.That’s a lot of evolution in the blink of a geological eye.  Nowhere did the article indicate how the authors tied these innovations to random mutations.  In fact, the flavor of the entire article is Lamarckian.  A need exists, so the environment delivers (cf. 04/20/2008).  This does not dismiss the null hypothesis that needs might go unfulfilled, nor does it explain why the primitive solutions survived quite well for hundreds of millions of years.    Since hagfish and lampreys provide a key milestone on Lamb et al’s map of eye evolution, let’s look at a different paper on the topic.  In the Journal of Experimental Biology this month,1 two Swedes and an Australian published a paper right on this point: the evolution of focusing eyes in lampreys.  Their abstract reveals a less optimistic attitude:Jawless fishes (Agnatha; lampreys and hagfishes) most closely resemble the earliest stage in vertebrate evolution and lamprey-like animals already existed in the Lower Cambrian [about 540 million years ago (MYA)].  Agnathans are thought to have separated from the main vertebrate lineage at least 500 MYA.  Hagfishes have primitive eyes, but the eyes of adult lampreys are well-developed.  The southern hemisphere lamprey, Geotria australis, possesses five types of opsin genes, three of which are clearly orthologous to the opsin genes of jawed vertebrates.  This suggests that the last common ancestor of all vertebrate lineages possessed a complex colour vision system.  In the eyes of many bony fishes and tetrapods, well-focused colour images are created by multifocal crystalline lenses that compensate for longitudinal chromatic aberration.  To trace the evolutionary origins of multifocal lenses, we studied the optical properties of the lenses in four species of lamprey… with representatives from all three of the extant lamprey families.  Multifocal lenses are present in all lampreys studied.  This suggests that the ability to create well-focused colour images with multifocal optical systems also evolved very early.So even though coming from an evolutionary perspective, this says their findings reduce the time for all the innovation required in Lamb et al’s Stage Four.  The hagfish is not an intermediate.  Whatever was ancestor to lampreys and hagfishes already had the equipment and know-how to focus optical images.  By implication, this includes the rest of the toolkit: retinal cells, ganglion cells, optic nerves and a brain to interpret them in living color.    Get an eyeful of this: the BBC News has a picture of the lens from a giant squid.  This denizen of the dark ocean depths has the largest eyeball of any known animal – 11 inches in diameter.  The squid’s “truly amazing eyes” are probably the largest of any animal living or extinct.  National Geographic has photos of the monster.    Squid belong to the mollusk Cephalopod class, which originated in the late Cambrian.  Though octopus and squid are said to have evolved later, the presence of complex, focusing, retinal eyes presents another evolutionary problem.  Either these eyes developed completely independently by “convergent evolution,” or the common ancestor of cephalopods and lampreys already possessed the complex genetic toolkit for focusing color vision.    A paper in Nature May 15 makes this remarkable statement: “human melanopsin – which on the basis of sequence similarity – is more closely related to invertebrate than to vertebrate rhodopsin.”2  In fact, the similarities between the light-sensitive proteins of animals from completely different branches of Darwin’s tree is striking: “The crystal structure shows that the arrangement of helices I to VIII is similar to that of the rhodopsins isolated from frogs and cattle, so the overall three-dimensional structure of the protein is very similar in vertebrates and invertebrates.”  Differences seem attributable to the different environments of the respective animals.1.  Gustaffson, Collin and Kroger, “Early evolution of multifocal optics for well-focused colour vision in vertebrates,” Journal of Experimental Biology 211, 1559-1564 (2008), published online May 2, 2008 by The Company of Biologists 2008, doi: 10.1242/jeb.016048.2.  Gebhard F. X. Schertler, “Signal transduction: The rhodopsin story continued,” Nature 453, 292-293 (15 May 2008) | doi:10.1038/453292a.Where has Kate McDonald been?  Where has she been getting her information about creationism and intelligent design?  Certainly not here; we have a string of articles from 2000 to the present revealing that severe challenges to “eye evolution” show no signs of abating (see, for instance, as recently as 03/31/2008 and its embedded links to earlier entries; also 07/17/2006, 05/22/2003).  Every time the Darwinists have tried to blind the public by bluffing about the evolution of vision we have poked them right back in the proverbial eye with the facts (e.g., 12/13/2007, 09/29/2006, 09/22/2005).  If McDonald thinks the debate has gotten quiet on the creationist side she’s got fingers in her ears as well as her eyes closed.    Anyone who thinks this latest manufactured five-stage fictional plot about how eyes evolved has any credibility should notice that the Gustaffson et al paper made the story come apart in the middle.  Our watchful eyes don’t let evolutionists get away with bluffing.(Visited 17 times, 1 visits today)FacebookTwitterPinterestSave分享0last_img

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