The mystery of eye evolution
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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.
Now, now, be nice...
"I see", said the blind man, as he picked up a hammer and saw.
Been there, done that, wrote a rebuttal about the fundamental flaws in Behe's thesis (see below).
We are the product of intelligent design.
If you have evidence for such an assertion, please present it. And no, Behe's argument doesn't count.
I find it amazing that the evolutionists can believe that all of the universe can spring from a “Big Bang” (the size of the head of a pin)
Although the Big Bang is not actually related to biological evolution, the reason many of us believe it is because the evidence very strongly indicates it.
but do not believe that all was created from nothing.
What makes you think we don't?
And now my rebuttal to Behe, from this FR post and this one:
And:The next idea you probably will not like, and that is irreducible complexity.
As an "idea" I like it just fine, and so do evolutionary scientists. The problem is that Behe (and the creationists who follow him) have created a "straw man" version of "IC" which is quite simply incorrect -- but appears to give the conclusion they want.
The original notion of "IC" goes back to Darwin himself. He wrote:
"If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down."That's "Irreducible Complexity" in a nutshell. It's not as if Behe has pointed out anything that biologists (or Darwin) didn't already realize.
-- Charles Darwin, "On the Origin of Species", 1859But let's examine Darwin's description of "IC" in a bit more detail (emphasis mine):
No doubt many organs exist of which we do not know the transitional grades, more especially if we look to much-isolated species, round which, according to my theory, there has been much extinction. Or again, if we look to an organ common to all the members of a large class, for in this latter case the organ must have been first formed at an extremely remote period, since which all the many members of the class have been developed; and in order to discover the early transitional grades through which the organ has passed, we should have to look to very ancient ancestral forms, long since become extinct.Darwin makes two critical points here:We should be extremely cautious in concluding that an organ could not have been formed by transitional gradations of some kind. Numerous cases could be given amongst the lower animals of the same organ performing at the same time wholly distinct functions; thus the alimentary canal respires, digests, and excretes in the larva of the dragon-fly and in the fish Cobites. In the Hydra, the animal may be turned inside out, and the exterior surface will then digest and the stomach respire. In such cases natural selection might easily specialise, if any advantage were thus gained, a part or organ, which had performed two functions, for one function alone, and thus wholly change its nature by insensible steps. Two distinct organs sometimes perform simultaneously the same function in the same individual; to give one instance, there are fish with gills or branchiae that breathe the air dissolved in the water, at the same time that they breathe free air in their swimbladders, this latter organ having a ductus pneumaticus for its supply, and being divided by highly vascular partitions. In these cases, one of the two organs might with ease be modified and perfected so as to perform all the work by itself, being aided during the process of modification by the other organ; and then this other organ might be modified for some other and quite distinct purpose, or be quite obliterated.
The illustration of the swimbladder in fishes is a good one, because it shows us clearly the highly important fact that an organ originally constructed for one purpose, namely flotation, may be converted into one for a wholly different purpose, namely respiration. The swimbladder has, also, been worked in as an accessory to the auditory organs of certain fish, or, for I do not know which view is now generally held, a part of the auditory apparatus has been worked in as a complement to the swimbladder. All physiologists admit that the swimbladder is homologous, or 'ideally similar,' in position and structure with the lungs of the higher vertebrate animals: hence there seems to me to be no great difficulty in believing that natural selection has actually converted a swimbladder into a lung, or organ used exclusively for respiration.
[Example snipped]
In considering transitions of organs, it is so important to bear in mind the probability of conversion from one function to another, that I will give one more instance. [Long detail of example snipped] If all pedunculated cirripedes had become extinct, and they have already suffered far more extinction than have sessile cirripedes, who would ever have imagined that the branchiae in this latter family had originally existed as organs for preventing the ova from being washed out of the sack?
-- Charles Darwin, "On the Origin of Species", 1859
1. A modern organ need not have evolved into its present form and function from a precursor which had always performed the same function. Evolution is quite capable of evolving a structure to perform one function, and then turning it to some other "purpose".
2. Organs/structures can reach their present form through a *loss* of function or parts, not just through *addition* of function or parts.
Despite the fact that these observations were laid out in 1859, Behe's version of "Irreducible Complexity" pretends they are not factors, and defines "IC" as something which could not have arisen through stepwise *ADDITIONS* (only) while performing the same function *THROUGHOUT ITS EXISTENCE*.
It's hard to tell whether Behe does this through ignorance or willful dishonesty, but the fact remains that *his* definition and analysis of "IC" is too restrictive. He places too many "rules" on how he will "allow" evolution to reach his examples of "Behe-style IC" structures, while evolution itself *IS NOT RESTRICTED TO THOSE RULES* when it operates. Thus Behe's conclusion that "Behe-style evolution" can not reach "Behe-style IC" hardly tells us anything about whether *real-world* evolution could or could not have produced them.
For specific examples, Behe's example of the "Behe-style IC" flagellum is flawed because flagella are composed of components that bacteria use FOR OTHER PURPOSES and were evolved for those purposes then co-opted (1, 2), and Behe's example of the "Behe-style IC" blood-clotting process is flawed because the biochemistry of blood-clotting is easily reached by adding several steps on top of a more primitive biochemical sequence, *and then REMOVING earlier portions which had become redundant* (1, 2).
Even Behe's trivial mousetrap example turns out to not actually be "IC".
The usual qualitative formulation is: "An irreducibly complex system cannot be produced...by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system, that is missing a part is by definition nonfunctional..."
Note the key error: By saying that it "breaks" if any part is "missing" (i.e. taken away), it is only saying that evolution could not have reached that endpoint by successively only ADDING parts. True enough, but Behe misses the fact that you can also reach the same state by, say, adding 5 parts one at a time, and then taking away 2 which have become redundant. Let's say that part "A" does the job, but not well. But starting with just "A" serves the need. Then add "B", which improves the function of "A". Add "C" which helps A+B do their job, and so on until you have ABCDE, which does the job very well. Now, however, it may turn out that CDE alone does just fine (conceivably, even better than ABCDE does with A+B getting in the way of CDE's operation). So A and B fade away, leaving CDE. Note that CDE was built in "one change at a time" fashion, with each new change improving the operation. HOWEVER, by Behe's definition CDE is "Irreducibly Complex" and "could not have evolved (been built by single steps)" because removing C or D or E from CDE will "break" it. Note that Behe's conclusion is wrong. His logic is faulty.
The other error in Behe's definition lies in this part: "...any precursor to an irreducibly complex system, that is missing a part is by definition nonfunctional". The problem here is that it may be "nonfunctional" for its *current* function, but perfectly functional for some *other* function helpful for survival (and therefore selected by evolution). Behe implicitly claims that if it's not useful for its *current* function, it's useless for *any* function. The flaw in this should be obvious.
"Since natural selection can only choose systems that are already working, then if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on."
True as far as it goes, but but this is hardly the same as Behe's sleight-of-hand in the first part of his statement, which relies on the false premise that a precursor to a structure is 100% useless for *any* purpose if *taking away* (but not adding) one part from the current purpose makes it unsuitable for the current purpose. Two gaping holes in that one...
Behe (an anathematized name)
For reasons I've outlined above.
talks of the bacterial flagellum, which contains an acid-powered rotary engine, a stator, O-rings, bushings, and a drive shaft. The machinery of this motor requires approximately fifty proteins.
Except that it doesn't. As many biochemists have pointed out, other organisms have function flagella (even *as* flagella) with fewer proteins (and/or different proteins). That flagellum isn't even "IC" by Behe's own definition since you *can* remove proteins and have it still work as a flagellum. [...]
Finally, your entire exercise misses the boat entirely. Yes, as you've shown, the odds of a particular flagellar structure arising "from the ground up" in one "step" entirely by random chance of jostling amino acids is practically nil and probably never happened.
But so what? No one's suggesting that it *did* happen that way.
Instead, biologists believe that the flagella arose over a *long* period of accumulated improvements and increased complexity, through evolutionary processes (which weed out the failures while multiplying and accumulating successes), eventually producing that particular modern flagellum by a final combination of *pre-existing* proteins and components available in the cell which had been mostly developed for other purposes. For example, in the case of Behe's favorite flagella, the common bacterial type III export apparatus (used for transporting specific proteins out of the cytoplasm) is recognizably the core of the "motor" of the the flagellum. So the proteins which were developed (through evolution) to provide *that* functionality did *NOT* have to be randomly assembled "from scratch" in order to "luckily" produce the flagellum out of pure raw amino acids, as your calculation presumed. Instead, those proteins were *already present*. How much does that cut down the set of 50, eh? Likewise for other proteins and structures which were already present in the cell but later co-opted for flagellar use. Your entire "all from scratch all at once" calculation is quite simply irrelevant, since it totally fails to take into account things which we *know* were already present in the cell (for *other* purposes -- something Behe keeps forgetting or trying to hide), and therefore did not have to be "invented" randomly on the fly as your calculation requires.
For a far more realistic look at the evolutionary "invention" of the flagellum, see Evolution in (Brownian) space: a model for the origin of the bacterial flagellum , which I linked earlier in this post. From the abstract:
The model consists of six major stages: export apparatus, secretion system, adhesion system, pilus, undirected motility, and taxis-enabled motility. The selectability of each stage is documented using analogies with present-day systems. Conclusions include: (1) There is a strong possibility, previously unrecognized, of further homologies between the type III export apparatus and F1F0-ATP synthetase. (2) Much of the flagellum’s complexity evolved after crude motility was in place, via internal gene duplications and subfunctionalization. (3) Only one major system-level change of function, and four minor shifts of function, need be invoked to explain the origin of the flagellum; this involves five subsystem-level cooption events. (4) The transition between each stage is bridgeable by the evolution of a single new binding site, coupling two pre-existing subsystems, followed by coevolutionary optimization of components. Therefore, like the eye contemplated by Darwin, careful analysis shows that there are no major obstacles to gradual evolution of the flagellum.Now *that's* science. Behe's stuff is just hand-waving and ivory-tower blowhardedness.
As for Behe (the other author):
One small example is the flagella on a paramecium. They need four distinct proteins to work.
Actually they need a lot more than that. And as far as I know, Behe never used the cilia on paramecia as his example, he has primarily concentrated on bacterial flagella.
They cannot have evolved from a flagella that need three.
Contrary to creationist claims (or Behe's) that flagella are Irreducibly Complex and can not function at all if any part or protein is removed, in fact a) there are many, many varieties of flagella on various species of single-celled organisms, some with more or fewer parts/proteins than others. So it's clearly inaccurate to make a blanket claim that "flagella" in general contain no irreplacable parts. Even Behe admits that a working flagella can be reduced to a working cilia, which undercuts his entire "Irreducibly Complex" example/claim right off the bat.
For a semi-technical discussion of how flagella are *not* IC, because many of their parts can be eliminated without totally breaking their locomotive ability, see Evolution of the Bacterial Flagella
But even if one could identify, say, four specific proteins (or other components) which were critically necessary for the functioning of all flagellar structures (and good luck: there are three unrelated classes of organisms with flagella built on three independent methods: eubacterial flagella, archebacterial flagella, and eukaryote flagella -- see Faugy DM and Farrel K, (1999 Feb) A twisted tale: the origin and evolution of motility and chemotaxis in prokaryotes. Microbiology, 145, 279-280), Behe makes a fatal (and laughably elementary) error when he states that therefore they could not have arisen by evolution. Even first-year students of evolutionary biology know that quite often evolved structures are built from parts that WERE NOT ORIGINALLY EVOLVED FOR THEIR CURRENT APPLICATION, as Behe naively assumes (or tries to imply).
Okay, fine, so even if you can prove that a flagellum needs 4 certain proteins to function, and would not function AS A FLAGELLUM with only 3, that's absolutely no problem for evolutionary biology, since it may well have evolved from *something else* which used those 3 proteins to successfully function, and only became useful as a method of locomotion when evolution chanced upon the addition of the 4th protein. Biology is chock-full of systems cobbled together from combinations of other components, or made via one addition to an existing system which then fortuitously allows it to perform a new function.
And, lo and behold, it turns out that the "base and pivot" of the bacterial flagella, along with part of the "stalk", is virtually identical to the bacterial Type III Secretory Structure (TTSS). So despite Behe's claim that flagella must be IC because (he says) there's no use for half a flagella, in fact there is indeed such a use. And this utterly devastates Behe's argument, in several different ways. Explaining way in detail would take quite some time, but it turns out that someone has already written an excellent essay on that exact thing, which I strongly encourage you to read: The Flagellum Unspun: The Collapse of "Irreducible Complexity" .
(Note: Several times that essay makes a reference to the "argument from ignorance", with the assumption that the reader is already familiar with it. I'd like to point out that contrary to the way it sounds, Miller is *not* accusing Behe et all of being ignorant. Instead, he's referring to this family of logical fallacies, also known as the "argument from incredulity".)
That is called irreducible complexity.
That's what Behe likes to call it, yes. But the flagella is provably *not* IC. Oops for Behe. Furthermore, while it's certainly easy to *call* something or another "Irreducibly Complex", proving that it actually *is* is another matter entirely.
As the "Flagellum Unspun" article above states:
According to Dembski, the detection of "design" requires that an object display complexity that could not be produced by what he calls "natural causes." In order to do that, one must first examine all of the possibilities by which an object, like the flagellum, might have been generated naturally. Dembski and Behe, of course, come to the conclusion that there are no such natural causes. But how did they determine that? What is the scientific method used to support such a conclusion? Could it be that their assertions of the lack of natural causes simply amount to an unsupported personal belief? Suppose that there are such causes, but they simply happened not to think of them? Dembski actually seems to realize that this is a serious problem. He writes: "Now it can happen that we may not know enough to determine all the relevant chance hypotheses [which here, as noted above, means all relevant natural processes (hvt)]. Alternatively, we might think we know the relevant chance hypotheses, but later discover that we missed a crucial one. In the one case a design inference could not even get going; in the other, it would be mistaken" (Dembski 2002, 123 (note 80)).For more bodyblows against the notion of Irreducible Complexity, see:Bacterial Flagella and Irreducible Complexity
Irreducible Complexity Demystified
Review: Michael Behe's "Darwin's Black Box"
If the human eye is perfect, why does it go to crap after about forty years (he wrote while peering through his bifocals)...
Plus I'm miffed that I can't see ultraviolet, my vision is inferior to an insect's. "Perfect" my butt.
Oh, I see. But then by your own reasoning, God couldn't have happened unless there was something there before him. What was it? And what was there before that? And before that?
Warning: Whichever way you answer this, you will be hoist on your own petard. So consider that there may be something wrong with your premise.
SAME question.
Why did God have to come from anywhere?
Why did the realm from which the Universe sprang have to come from anywhere?
God is infinite, and therefore, always was and always will be. God created time for our benefit, but is not bound by His creation.
The substrate of the Universe is infinite, and therefore, always was and always will be. From it sprang time, but it is not bound by time.
There, now, see how easy that is?
The universe, on the other hand, had to have a beginning.
The predecessor of the Universe, on the other hand, didn't.
There, just as good as your version.
Why did God send a bear to rip apart the children who were making fun of a man's baldness?
Science makes no such attempt, nor do most people apply science to that pursuit.
Stick around these threads for any length of time however, and you'll meet plenty of people who seem awfully defensive about their deity, see "attacks" whenever science is simply being discussed, and try to disprove the parts of science which they apparently have trouble reconciling with their view of their deity.
The origin I seek you to explain is the biginnig of this ball of wax.. this time, matter, energy, space continuum which we refer to as the universe. Perhaps you will be helped with a fill in the blank...In the beginning..................... In refence to your observation that your analysis of Budhism, I will digress for a moment. There are 2 Great Religious tennants comparative religious scolars agree on. One is Monotheism..a transendent God..Judaochristian thesis and a radical offshoot Islam. The worship a transendent God. The second is Pantheism...All is god...you, me ,the rocks,trees,everything....All is part of god. From that tenent springs Hinduism (all is god) Budhism all is conscienceness which is simply recycled to the great collective unconscience, an idea which was borrowed by a greatly from the heir apparent of Sigmund Freud,an austrian psychologist named Carl Jung, who propounded the theory of the collective unconscience. We could include Abraham Maslow and his theory of heirchical developemnt. There is not a dimes worth of difference in these ideas. But for now we may want to set aside the religion of Psychology (study of the soul) for now.. I am still trying to get you to instruct me as to how the universe came into being. That great moment where energy and matter came into being and began to disperse into a vast vacuous space. When did it begin and what initiated it. Please don't waist the readers time and refer to the Big Bang and the expansion theory or the ossilation contraction theory. What was before this?
To give you something to complain about...
Haven't you ever heard of "bear-baiting"?
Perhaps you could help Mr. Dimensio in explaining the answer to my question. I assure you I am not defensive about my deity. I do not see science as an attack on my faith. I simply have not yet seen either of you answer my simple question from your platform of science.So please explain to me what was the very beginning...you know where the universe and all that is in it began. Once your science convinces me I will be pulled to your side and will advocate what you teach me, if it is truth.
You clearly don't understand the meaning of either term...
Out of nothing the vertebrate eye is supposed to have developed completely separate from the squid and octopus which they (Darwinians) say developed from different phylogenetic lineages.
Incorrect -- from what box of Cracker Jacks did you gain your "science" education? Or was it from a creationist screed, which is equally unreliable?
The vertebrate eye did not develop "out of nothing", its development was separate but not "completely separate" from that of the cephalopod eye, and the term "different phylogenetic lineages" is a relative term, which you are incorrectly using as an absolute -- go back far enough and we most certainly *are* in the same phylogenetic lineage as the invertebrates.
Just got lucky I guess.
Just your straw man I guess.
When they say "If you put a chimpanzee in from of an IBM selectric typewriter and he struck 60 elements per minute,given enough time he would exactly duplicate the exact works of Shakespeare." That is an article of faith any way you slice it.
No, that's mathematics, and it's provably true. But your example has nothing to do with evolution, convergent or otherwise, since evolution does not proceed via unaided randomness.
Is your non sequitur due to ignorance, or disingenuousness?
Call it science if you like, but it aint.
What you're putting into your posts certainly "ain't", that's for sure. If you want to discuss what science *actually* holds, instead of your cartoon version of it, feel free to start at any time.
By your own "rule", you can't determine whether a god made the universe, because none of us were there to watch it.
In any case, the childish assertion that science requires "an observer" on the scene (or that anything determined without an eyewitness is nothing more than "faith") is laughably wrong.
Watch any of the plethora of "crime scene investigation" TV dramas which are running this year, if you want a taste -- they're all about how science is used to determine what happened at a crime scene beyond a shadow of a doubt, BASED ON EVIDENCE, and WITHOUT having the luxury of having a witness (or the killer) simply write a narrative report of the events.
Please, before you attempt to critique science -- learn something about how it works.
EEERRRNNT... Sorry, wrong answer, thanks for playing.
Go read up on "emergent properties" (not just that starter web page, but the entire field) and get back to us when your argument isn't uselessly simplistic and fallaciously reductionist.
It leads you to nihilism and hopelessness.
It would only lead me there if I misunderstood the issue as badly as you do.
Please exlain to me where I am wrong.
The whole is greater than the sum of its parts. This is why a computer can perform mathematics whereas a rock can't, even though both are made up of silicon compounds.
So rabbits really *do* chew cud? Fascinating.
Anyone who wishes to do so can do the same, and come to their own conclusions.
Way ahead of you.
Sorry, but the flaws in Pascal's Wager have been recognized for centuries. The primary one is that it is an equally "good" argument for worshipping Shiva, Thor, Quetzlcotl, or Satan.
How... convenient.
You have already made up your mind,
No, actually, we have not, and that's the whole point. We are always open to having our minds changed by new evidence. This is why we ask you for the evidence you claim to have, so that we can evaluate it for ourselves.
and as long as you can live with it, I can as well.
I can live with being open to new evidence, ideas, and arguments.
Neither am I, but if you are under the impression that anyone here, or any prominent scientist, does such a thing, you are quite mistaken, and unnecessarily defensive.
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