Posted on 11/03/2004 5:11:47 PM PST by general_re
Darwin's greatest challenge tackled
The mystery of eye evolution
Researchers provide concrete evidence about how the human eye evolved
When Darwin's skeptics attack his theory of evolution, they often focus on the eye. Darwin himself confessed that it was 'absurd' to propose that the human eye, an 'organ of extreme perfection and complication' evolved through spontaneous mutation and natural selection. But he also reasoned that "if numerous gradations from a simple and imperfect eye to one complex and perfect can be shown to exist" then this difficulty should be overcome. Scientists at the European Molecular Biology Laboratory [EMBL] have now tackled Darwin's major challenge in an evolutionary study published this week in the journal Science. They have elucidated the evolutionary origin of the human eye.
Researchers in the laboratories of Detlev Arendt and Jochen Wittbrodt have discovered that the light-sensitive cells of our eyes, the rods and cones, are of unexpected evolutionary origin they come from an ancient population of light-sensitive cells that were initially located in the brain.
"It is not surprising that cells of human eyes come from the brain. We still have light-sensitive cells in our brains today which detect light and influence our daily rhythms of activity," explains Wittbrodt. "Quite possibly, the human eye has originated from light-sensitive cells in the brain. Only later in evolution would such brain cells have relocated into an eye and gained the potential to confer vision."
The scientists discovered that two types of light-sensitive cells existed in our early animal ancestors: rhabdomeric and ciliary. In most animals, rhabdomeric cells became part of the eyes, and ciliary cells remained embedded in the brain. But the evolution of the human eye is peculiar it is the ciliary cells that were recruited for vision which eventually gave rise to the rods and cones of the retina.
So how did EMBL researchers finally trace the evolution of the eye?
By studying a 'living fossil,' Platynereis dumerilii, a marine worm that still resembles early ancestors that lived up to 600 million years ago. Arendt had seen pictures of this worm's brain taken by researcher Adriaan Dorresteijn [University of Mainz, Germany]. "When I saw these pictures, I noticed that the shape of the cells in the worm’s brain resembled the rods and cones in the human eye. I was immediately intrigued by the idea that both of these light-sensitive cells may have the same evolutionary origin."
To test this hypothesis, Arendt and Wittbrodt used a new tool for today’s evolutionary biologists – 'molecular fingerprints'. Such a fingerprint is a unique combination of molecules that is found in a specific cell. He explains that if cells between species have matching molecular fingerprints, then the cells are very likely to share a common ancestor cell.
Scientist Kristin Tessmar-Raible provided the crucial evidence to support Arendt's hypothesis. With the help of EMBL researcher Heidi Snyman, she determined the molecular fingerprint of the cells in the worm's brain. She found an opsin, a light-sensitive molecule, in the worm that strikingly resembled the opsin in the vertebrate rods and cones. "When I saw this vertebrate-type molecule active in the cells of the Playtnereis brain – it was clear that these cells and the vertebrate rods and cones shared a molecular fingerprint. This was concrete evidence of common evolutionary origin. We had finally solved one of the big mysteries in human eye evolution."
Source Article
Ciliary photoreceptors with vertebrate-type opsins in an invertebrate brain.
D. Arendt, K. Tessmar-Raible, Snyman, Dorresteijn, J. Wittbrodt
Science. October 29, 2004.
Wow, that sure is a lot of hand-waving. Most of it breaks down to a) the Bible was copied a lot but not changed during much during the copying (does not confirm that the *contents* are accurate), b) Jesus didn't complain about the accuracy of the sciptures (begs the question), c) apparent contradictions and errors can be explained away (as always -- whether the explanations are good or not is another issue), or d) it contains confirmed historical settings or events (well so does "Gone With the Wind", but it's still fiction).
The final category, "fulfilled predictions/prophecies", is at least in concept more convincing, but falls down when you look at specific examples, which include such underwhelming cases such as "prophecies" so general that they were bound to come true in *some* sense, self-fulfilling prophecies, and prophecies which can't be proven to have been made before the events they described, etc.
Hydrogen, acted upon by gravity.
The Path from the RNA World Anthony M. Poole, Daniel C. Jeffares, David Penny: Institute of Molecular Biosciences, Massey UniversityAnd:Abstract: We describe a sequential (step by step) Darwinian model for the evolution of life from the late stages of the RNA world through to the emergence of eukaryotes and prokaryotes. The starting point is our model, derived from current RNA activity, of the RNA world just prior to the advent of genetically-encoded protein synthesis. By focusing on the function of the protoribosome we develop a plausible model for the evolution of a protein-synthesizing ribosome from a high-fidelity RNA polymerase that incorporated triplets of oligonucleotides. With the standard assumption that during the evolution of enzymatic activity, catalysis is transferred from RNA M RNP M protein, the first proteins in the ``breakthrough organism'' (the first to have encoded protein synthesis) would be nonspecific chaperone-like proteins rather than catalytic. Moreover, because some RNA molecules that pre-date protein synthesis under this model now occur as introns in some of the very earliest proteins, the model predicts these particular introns are older than the exons surrounding them, the ``introns-first'' theory. Many features of the model for the genome organization in the final RNA world ribo-organism are more prevalent in the eukaryotic genome and we suggest that the prokaryotic genome organization (a single, circular genome with one center of replication) was derived from a ``eukaryotic-like'' genome organization (a fragmented linear genome with multiple centers of replication). The steps from the proposed ribo-organism RNA genome M eukaryotic-like DNA genome M prokaryotic-like DNA genome are all relatively straightforward, whereas the transition prokaryotic-like genome M eukaryotic-like genome appears impossible under a Darwinian mechanism of evolution, given the assumption of the transition RNA M RNP M protein. A likely molecular mechanism, ``plasmid transfer,'' is available for the origin of prokaryotic-type genomes from an eukaryotic-like architecture. Under this model prokaryotes are considered specialized and derived with reduced dependence on ssRNA biochemistry. A functional explanation is that prokaryote ancestors underwent selection for thermophily (high temperature) and/or for rapid reproduction (r selection) at least once in their history.
On the origins of cells: a hypothesis for the evolutionary transitions from abiotic geochemistry to chemoautotrophic prokaryotes, and from prokaryotes to nucleated cells William Martin and Michael J. RussellAnd:Abstract: All life is organized as cells. Physical compartmentation from the environment and self-organization of self-contained redox reactions are the most conserved attributes of living things, hence inorganic matter with such attributes would be life’s most likely forebear. We propose that life evolved in structured iron monosulphide precipitates in a seepage site hydrothermal mound at a redox, pH and temperature gradient between sulphide-rich hydrothermal fluid and iron(II)-containing waters of the Hadean ocean floor. The naturally arising, three-dimensional compartmentation observed within fossilized seepage-site metal sulphide precipitates indicates that these inorganic compartments were the precursors of cell walls and membranes found in free-living prokaryotes. The known capability of FeS and NiS to catalyse the synthesis of the acetyl-methylsulphide from carbon monoxide and methylsulphide, constituents of hydrothermal fluid, indicates that pre-biotic syntheses occurred at the inner surfaces of these metal-sulphide-walled compartments, which furthermore restrained reacted products from diffusion into the ocean, providing sufficient concentrations of reactants to forge the transition from geochemistry to biochemistry. The chemistry of what is known as the RNA-world could have taken place within these naturally forming, catalyticwalled compartments to give rise to replicating systems. Sufficient concentrations of precursors to support replication would have been synthesized in situ geochemically and biogeochemically, with FeS (and NiS) centres playing the central catalytic role. The universal ancestor we infer was not a free-living cell, but rather was confined to the naturally chemiosmotic, FeS compartments within which the synthesis of its constituents occurred. The first free-living cells are suggested to have been eubacterial and archaebacterial chemoautotrophs that emerged more than 3.8 Gyr ago from their inorganic confines. We propose that the emergence of these prokaryotic lineages from inorganic confines occurred independently, facilitated by the independent origins of membrane-lipid biosynthesis: isoprenoid ether membranes in the archaebacterial and fatty acid ester membranes in the eubacterial lineage. The eukaryotes, all of which are ancestrally heterotrophs and possess eubacterial lipids, are suggested to have arisen ca. 2 Gyr ago through symbiosis involving an autotrophic archaebacterial host and a heterotrophic eubacterial symbiont, the common ancestor of mitochondria and hydrogenosomes. The attributes shared by all prokaryotes are viewed as inheritances from their confined universal ancestor. The attributes that distinguish eubacteria and archaebacteria, yet are uniform within the groups, are viewed as relics of their phase of differentiation after divergence from the non-free-living universal ancestor and before the origin of the free-living chemoautotrophic lifestyle. The attributes shared by eukaryotes with eubacteria and archaebacteria, respectively, are viewed as inheritances via symbiosis. The attributes unique to eukaryotes are viewed as inventions specific to their lineage. The origin of the eukaryotic endomembrane system and nuclear membrane are suggested to be the fortuitous result of the expression of genes for eubacterial membrane lipid synthesis by an archaebacterial genetic apparatus in a compartment that was not fully prepared to accommodate such compounds, resulting in vesicles of eubacterial lipids that accumulated in the cytosol around their site of synthesis. Under these premises, the most ancient divide in the living world is that between eubacteria and archaebacteria, yet the steepest evolutionary grade is that between prokaryotes and eukaryotes.
The emergence of life from iron monosulphide bubbles at a submarine hydrothermal redox and pH front M. J. RUSSELL & A. J. HALL: Department of Geology and Applied Geology, University of GlasgowAbstract: Here we argue that life emerged on Earth from a redox and pH front at c. 4.2 Ga. This front occurred where hot (c. 150)C), extremely reduced, alkaline, bisulphide-bearing, submarine seepage waters interfaced with the acid, warm (c. 90)C), iron-bearing Hadean ocean. The low pH of the ocean was imparted by the ten bars of CO2 considered to dominate the Hadean atmosphere/hydrosphere. Disequilibrium between the two solutions was maintained by the spontaneous precipitation of a colloidal FeS membrane. Iron monosulphide bubbles comprising this membrane were inflated by the hydrothermal solution upon sulphide mounds at the seepage sites. Our hypothesis is that the FeS membrane, laced with nickel, acted as a semipermeable catalytic boundary between the two fluids, encouraging synthesis of organic anions by hydrogenation and carboxylation of hydrothermal organic primers. The ocean provided carbonate, phosphate, iron, nickel and protons; the hydrothermal solution was the source of ammonia, acetate, HS", H2 and tungsten, as well as minor concentrations of organic sulphides and perhaps cyanide and acetaldehyde. The mean redox potential (ÄEh) across the membrane, with the energy to drive synthesis, would have approximated to 300 millivolts. The generation of organic anions would have led to an increase in osmotic pressure within the FeS bubbles. Thus osmotic pressure could take over from hydraulic pressure as the driving force for distension, budding and reproduction of the bubbles. Condensation of the organic molecules to polymers, particularly organic sulphides, was driven by pyrophosphate hydrolysis. Regeneration of pyrophosphate from the monophosphate in the membrane was facilitated by protons contributed from the Hadean ocean. This was the first use by a metabolizing system of protonmotive force (driven by natural ÄpH) which also would have amounted to c. 300 millivolts. Protonmotive force is the universal energy transduction mechanism of life. Taken together with the redox potential across the membrane, the total electrochemical and chemical energy available for protometabolism amounted to a continuous supply at more than half a volt. The role of the iron sulphide membrane in keeping the two solutions separated was appropriated by the newly synthesized organic sulphide polymers. This organic take-over of the membrane material led to the miniaturization of the metabolizing system. Information systems to govern replication could have developed penecontemporaneously in this same milieu. But iron, sulphur and phosphate, inorganic components of earliest life, continued to be involved in metabolism.
The architect of the universe tells me that you're wrong about that. And no, I'm not being facetious.
"It used to be, I was all messed up on drugs. But then, I found the Lord. Now, I'm all messed up on the Lord!"(I have *got* to get a sound clip of that sometime...)
-- line from a street preacher in a skit on an old "Cheech and Chong" album...
Yes, that's right, 94% of the last 50 posts are mine, what of it?
You've missed the point. It's established via standard, secular scholarship that the Bible is a near contemporaneous report of the events it describes. This is a strong indication of its accuracy.
How do you know Caesar conquered Gaul? Because of written history which is not as reliable as the Bible. Why would you believe Caesar conquered Gaul but not the Resurrection? Because of an emoition-based disbelief in the supernatural.
Go ahead and babble on and on...but you seem to be constrained by the God of science as postulated by the Enlightenment...You need to free your mind and at least wonder about other ways of understanding the evolution...not just Darwin's ways. In other words like other atheists you are too fixated on "proving" Creation wrong. Try thinking outside the box.
Caesar himself wrote an account of his conquests. It was widely distributed during his lifetime and thereafter. It's authorship has never been disputed. I read it in the original Latin when I was in school. Copies of it are still in print.
For the record I have in the past, and will again in the future, DEBATED this subject with intelligent, well educated people and I have thoroughly enjoyed doing so. I believe that DEBATING any issue is great intellectual stimulation, and it helps me to understand issues that are important to me. I either learn how to better present my point of view, or as is often the case, I learn from the point of view of my "opponent".
I will freely admit that I have not taken the time nor made the effort to make convincing arguments on this thread. My work and family commitments have prevented me from spending more than a few moments at a time at the computer (you may notice that my posts have been rather widely spaced). For that, I apologize.
When I do take the time to enter into a debate with someone, I like to do so with those, such as yourself, who have the intellectual capacity and education to actually challenge my beliefs. I will not, however, waste that time arguing with someone who is rude, combative, and arrogant. Along with intellect and education, a little civility comes in handy when engaging in a friendly debate. For these reasons, this will be my last post on this subject thread.
Is it too much to ask that you actually respond to something I've actually written, instead of just going off on rants about what you fantasize I might believe or want to do?
Sheesh.
Please begin at the beginning..before time,matter,energy..All I have asked you to do is explain how it all got started. It is difficult to discuss what happened after the beginning if you will not tell me how it all began.
Where did the hydrogen come from?
I will be glad to discuss Darwinian Models and other things you mention regarding the elements. But first things first. We must reconsile that the basic elements came into existence. Please explain this to me. Go to the origin. I have asked you a dozen times and you evade or attack. It is a simple question with an simple honest answer a purist scientist and atheist can easisly answser, and I as a Christian will understand. I'll give you hint...You don't have to answer God. You don't have to go back that far to procure the aswer to my question. But you cannot begin with Darwinian evolution,primordial soup, hydrogen, or any of the elements. Go to Orgin.
Beginning of *what*?
before time,matter,energy..
The astute reader will note that "before time" is an oxymoron.
All I have asked you to do is explain how it all got started.
And I have answered you. If you have found the answer somehow unsatisfactory, please clearly state why, instead of mechanically repeating the question.
It is difficult to discuss what happened after the beginning if you will not tell me how it all began.
Horse manure, but if that's what you want to go with as your excuse for not discussing biology, I won't press you on the subject.
From free protons and electrons.
If in this life only we have hope in Christ, we are of all men most miserable. - 1 Corinthians 15:19
And where are the gods you mention? They live only in the imagination of men.
No, apparently, you won't. As a diversion, you keep trying to discuss cosmology.
regarding the elements.
"The elements"? Oookay...
But first things first.
Ah, here comes the diversion again.
We must reconsile that the basic elements came into existence.
No, we "must" not. Your evasive tactic is as pointless and childish as someone who refuses to discuss the weather unless it is first determined how the air originated.
Please explain this to me. Go to the origin. I have asked you a dozen times and you evade or attack.
You have not asked me "a dozen times", and I have not "evaded or attacked". Please try to stick to facts.
It is a simple question with an simple honest answer a purist scientist and atheist can easisly answser,
Actually, the answer is *not* simple, but I have pointed you to sources which you can use as a starting point towards increasing your knowledge to the point where you can better understand the answer. But for some reason this does not satisfy you. Not my problem.
and I as a Christian will understand.
Somehow, I'm not reassured.
I'll give you hint...You don't have to answer God.
Tell me something I didn't already know.
You don't have to go back that far to procure the aswer to my question. But you cannot begin with Darwinian evolution,primordial soup, hydrogen, or any of the elements.
I already answered your question, and I did not "begin" with any of those things, so you should be happy.
Go to Orgin.
I have.
Look, you've made it clear you think you know "the" answer, so rather than play this game where you keep reasking the question when you don't like the answer I've already given, why don't you just explain your thoughts on the matter?
This "I'm just a small town boy for the heart of east Texas, and I just want to be educated" act is getting *really* old already, and it doesn't appear anyone's falling for it anyway.
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