Skip to comments.Insight into our sight: A new view on the evolution of the eye lens (Desperate conjuncture)
Posted on 09/22/2005 6:58:10 AM PDT by DaveLoneRanger
The evolution of complex and physiologically remarkable structures such as the vertebrate eye has long been a focus of intrigue and theorizing by biologists. In work reported this week in Current Biology, the evolutionary history of a critical eye protein has revealed a previously unrecognized relationship between certain components of vertebrate eyes and those of the more primitive light-sensing systems of invertebrates. The findings help clarify our conceptual framework for understanding how the vertebrate eye, as we know it, has emerged over evolutionary time.
The work is reported by Sebastian Shimeld at the University of Oxford and colleagues at the University of London and Radboud University in The Netherlands.
Our sight relies on the ability of our eye to form a clear, focused image on the retina. The critical component in focusing is the eye lens, and the physical properties that underlie the transparency of the lens, as well as its ability to precisely refract light, arise from the high concentrations of special proteins called crystallins found in lens cells.
Fish, frogs, birds and mammals all experience image-forming vision, thanks to the fact that their eyes all express crystallins and form a lens; however, the vertebrates' nearest invertebrate relatives, such as sea squirts, have only simple eyes that detect light but are incapable of forming an image. This has lead to the view that the lens evolved within the vertebrates early in vertebrate evolution, and it raises a long-standing question in evolutionary biology: How could a complex organ with such special physical properties have evolved?
In their new work, Shimeld and colleagues approached this question by examining the evolutionary origin of one crystallin protein family, known as the ß?-crystallins. Focusing on sea squirts, invertebrate cousins of the vertebrate lineage, the researchers found that these creatures possess a single crystallin gene, which is expressed in its primitive light-sensing system. The identification of the sea squirt's crystallin strongly suggests that it is the single gene from which the vertebrate ß?-crystallins evolved.
The researchers also found that, remarkably, expression of the sea squirt crystallin gene is controlled by genetic elements that also respond to the factors that control lens development in vertebrates: The researchers showed that when regulatory regions of the sea squirt gene are transferred to frog embryos, these regulatory elements drive gene expression in the tadpoles' own visual system, including the lens. This strongly suggests that prior to the evolution of the lens, there was a regulatory link between two tiers of genes: those that would later become responsible for controlling lens development, and those that would help give the lens its special physical properties. This combination of genes appears to have then been co-opted in an early vertebrate during the evolution of its visual system, giving rise to the lens.
How indeed? Once again, they don't admit to, or confess the enormous problem of eye evolution (which is sort of an oxymoron) until they think they've got it solved. This is where the argument from design comes in most strongly. The eye mechanism is far too complex to have evolved.
Everyone else, give me your feedback, but it looks like what they are saying is, these so-called "simple" forms of the eye in "simple" life forms like sea squirts and invertebrates are more similar to the "complex" forms than previously thought.
What do facts have to do with this topic?
You take a potato, give it glasses, stick it in the water and voila - you get eye evolved! Simple, works every time!
And here's my summary. IDers claim structures like the vertebrate lens contain multiple components that had to appear together to make a functioning eye, a putatively implausible occurence. Scientists reply that complex structures evolve, not de novo, but by co-option of pre-existing components which previously had other functions. And gosh, here's an example. Urochrodates don't have a vertebrate lens or ancillary strucutres, but they do have the vertebrate lens protein, which was already expressed for another purpose in the neuroectoderm.
It's not that ID needs to be refuted yet again; the only people who don't recognize it has already been refuted are true believers; but this is yet one more counter-example.
Still, thanks for posting it, Dave.
Since you are so impatient, I'll go ahead and paste some stuff on the biogeography nonproblem. I'm at college, I have a major test coming up, and I simply haven't time that all you unemployed frevolutionists seem to have on hand. As I said, it's about 35 to 1, and in print, that takes a little while. This pertains to an article National Geographic published.
As we travel down the "evolutionary ladder" to examine those creatures which were supposedly among the earliest life forms on the planet, would it not be logical to expect their eyes to be less complex? Contrary to this expectation, among the lowest rock layers are found multi-cellular creatures called trilobites which have an extremely sophisticated optical system. Some trilobites had a compound eye placed in such a way as to allow 360o vision.
Compound eyes are ideally suited for detecting minute motions and some trilobites eyes were specially designed to correct for spherical aberration allowing a clear image from each facet. Even more impressive, each lens allowed for undistorted underwater imaging depth perception. Thus, one of the "earliest" in vertebrate creatures had clear underwater vision through eyes which could detect both depth and imperceptibility small motions in all directions simultaneously. Yet this creature was not at the end of the supposed evolutionary line but near the beginning! Yet no direct ancestor to this incredible complex creature (or its eye) has been found.
The complexity of eyes still argue for the reality of instantaneous formation by an incredibly intelligent designer. There is neither a fossil record showing that the eye evolved nor any testable observations explain how it could possible happen.
With these facts in mind, why do we allow textbook selection which leaves out both the problems with evolution and the evidence for intelligent design? This is indoctrination, not education.
This is how science works. I see no problems here.
However, Darwin claimed that evolution explained the pattern of life on fixed continents, while now evolution is supposed to explain the pattern of life on continents that moved apart from one big one. If evolution is so flexible that it can explain such mutually incompatible distributions, then it explains nothing at all.
I'll be charitable and say that this writer is simply ignorant of the fact that Darwin spent five years on the H.M.S. Beagle investigating places like the Galapagos islands, and brought home hundreds of pages of notes and many specimens, then studied and thought for the next 20 years before publishing Origin of Species. If you'd read the Watson piece I linked to, you would've seen that Watson is remarking on Darwin's amazement at what he found on the islands of the Pacific.
Of course, the other alternative is that the writer knows this very well, but is so hard up for an argument that he has to lie to his readers about what Darwin actually thought and wrote.
Come on, man, have the decency to point me towards arguments by people who either know something or at least aren't charlatans.
Heh heh, sounds like you need to be on my Creation ping list. 8-)
By all means add me. :o)
Is that supposed to mean the four or five thousand years which has passed between the time that tyranosaur died and the present time when researchers break open one of its leg bones and find what looks like raw hamburger meat?
Gee, I thought it was millions or billions of years, depending which silly evolutionary theory they are trying to prove.
Did they find any bird DNA in it yet?
A physicist said "In science anything other than physics is stamp collecting"
I'd say he's about right. All opinion all the time.
Hadn't heard about any DNA studies. But anybody who thinks that meat is 65,000,000 years old is dillusional.
Let them think that, it puts them into a corner. If this meat survived unchanged for 65 million years, then evolution clearly didn't happen.
What did they previously "carbon date" these bones at? It proves their carbon dating "science" (although that has been proven wrong many other ways already)Is garbage as well. They do the same thing with arrow heads they find from "prehistoric man". They don't realize that this "prehistoric man" simply made an arrowhead out of a rock he found, which could have been from a much earlier time. The "cave man" didn't make the rock as well. Walk into any museum where they have these arrowheads neatly arranged and "dated" and point that out to the person running the show.
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