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Blind cave fish see the light

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Two blind fish can make sighted offspring.

“The offspring of crossbred blind cave fish see like their surface-dwelling cousins.

The results in Current Biology 1, show that the two populations took different evolutionary paths to blindness.

“We’ve basically shown that these different populations have converged upon the same outward appearance independently, and that they use different genes to do it”, says Richard Borowsky of New York University.”

This is the type of thing that RM and NS can do. I would say that they lose different genes to become blind, not use different genes.

Comments
[…] species will crash the party sporting functional lateral eyes. Something similar happened to the “blind” cave fish).Eyes went vestigial in total darkness, but hybridization started to bring them […]A 305 million year old harvestman fossil has two set of eyes | Uncommon Descent
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[...] bacteria evolve antibiotic resistance by junking intricate machinery, not by creating it. Cave fish lose their eyes. But we don’t need a theory for how intricate machinery gets wrecked. We need a theory [...]My op-ed piece in The Calgary Herald - Albertans right to reject Darwinian evolution | Uncommon Descent
August 17, 2008
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Mutations can break things easily; it's much harder to make things. There are many possible ways a mutation could break eyesight (think of all the causes of human blindness for comparison). So ‘when you cross them, the genetic deficiencies in one lineage are compensated for by strengths in the other, and vice-versa.’ The evos would be onto something if they could find a mutation that could generate sight de novo, instead of merely allowing already-existing sight information to be expressed. See CMI's article Let the blind see … Breeding blind fish with blind fish restores sight.Jonathan Sarfati
February 8, 2008
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this should be useful http://bric.postech.ac.kr/biotrend/science/science_view.php?nNum=91917ari-freedom
January 15, 2008
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I would also want to see PaV's evidnece relating to a mechanism whereby disuse of eyes is the trigger for eye-development repressing RNA to bee transmitted to its offspring.Clarence
January 14, 2008
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Well, PaV - show us your evidence. And also how it would explain the data in the paper (e.g. how you get 12 estimated QTLs if the inheritance isn't genetic, and also the pattern of complementation). BobBob O'H
January 13, 2008
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Bob #25: Here's a "just-so" story: through disuse of the eye, some type of RNA is transmitted to the progeny that is capable of repressing eye-development during embryonic growth. In the two populations, the RNA and its method of repression is slightly different. Since the genes needed for eye development are at no time absent, when these different populations are crossed, the differing RNAs don't interact in the same way as in each native population, and eyes develop. I like my "just-so" story better.PaV
January 13, 2008
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Vision is supposed to be very energy intensive, so another reason NS would tend to favor fish without the visual apparatus is that they would tend to have more metabolic energy to devote to food gathering, reproduction, etc.magnan
January 12, 2008
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I wish to concede a point about natural selection in this situation. I read an article that mentioned that fish eyes are subject to injury and infection, and that injury especially in total darkness would be greater as the fish can't avoid running into cave walls and the like. Injury of course leads to infection and infection to death. So natural selection very likely is favoring fish with no eyes over those with eyes. That said, whether the visual system is functional or not is still irrelevant. Loss of the whole eye and replaced by a tougher covering would be the thing that was favored. It seems reasonable to presume that eyesight was lost much more quickly than the whole eye as the visual system could be damaged in many ways that don't completely remove the eyeball.DaveScot
January 12, 2008
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Bob O'H asks "What about three blind mice?" If one of those three get their vision, the other two will disappear, because the first will "See how they're one."Q
January 11, 2008
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Oh, but I should mention the real question that lies unanswered from the story:
Two blind fish can make sighted offspring.
What about three blind mice? BobBob O'H
January 11, 2008
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PaV - no it's not a just-so story. The point of the work and the paper is that we now have the evidence (and, as I pointed out, sight was only partially restored in the cross where they found the QTLs). BobBob O'H
January 11, 2008
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"Loss of sight is caused by fixation of different alleles in different populations. If these are recessive, then crossing different populations will lead to full restoration of the phenotype." Is this a "just-so" story?PaV
January 11, 2008
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Another spin on this story is that Dawkins was right when he said evolving vision is really easy because it occurred 60 times in evolutionary history. ;-)idnet.com.au
January 11, 2008
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PaV - Yes, the blindness was overcome in one cross. This is not uncommon in genetics, and it well understood - it's called complementation (we were taught about it at undergraduate level). Loss of sight is caused by fixation of different alleles in different populations. If these are recessive, then crossing different populations will lead to full restoration of the phenotype. In the cross where they found the 2 QTL, the gene effects were estimated to be mostly additive, i.e. function was partly restored. If it was Lamarckian, how would they find 12 QTLs? And why would they find it in the crosses between individuals from different populations, but not from the same population (check the table in the online supplement)? BobBob O'H
January 11, 2008
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Bob O'H We can see the shadows moving around. We can tell if they're going left or right; but we're not sure exactly what they are. In the article it says that it took millenia to develop the blindness; yet the blindness is overcome in one cross. What are we dealing with? If 12 genes are involved, were 12 genes lost, causing the blindness; and now, you cross them, and boom, the 12 genes reappear? No, it's obviously the regulation of the genes that is at play here; the authors allude to that when they talk about a developmental program and such. I have a more Lamarckian view of all of this. Great patience will be required before we find out just what these "shadows" are, and what makes them move the way they do.PaV
January 11, 2008
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PaV @ 16 -
This sounds like speculation–and no more–on their part.
No, they actually carried out 2 generations of crosses, for several choices of cross. In one of the crosses, they even estimate that there are 12 genes (well, QTLs) involved. BobBob O'H
January 11, 2008
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I would also consider that this may be a nonrandom mutation triggered by the environmentari-freedom
January 11, 2008
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PaV, in 16, mentioned "This sounds like speculation–and no more–on their part." They did do an experiment, it seems. That is more than "no more". I read it as sound science - obsesrve, predict, experiment, confirm or reject the prediction. ----------------------- DaveScot mentions "It’s the absence of natural selection that explains it. Without natural selection acting as a conservative force random mutation runs rampant." If I understand correctly, all of these fish in each cave were blind. That suggests a selective bias towards blindness, and not simply ramant random mutation. Rampant random mutation would suggest a variety of blindess vs vision in the population. Since the bias did preserve one characterstic over another, why is that not an example of "natural selection acting as a conservative force?"Q
January 11, 2008
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Here's the critical passage: "Borowsky and his assistants descended into the caves and fished out different blind populations to cross in the lab. If the fish had the same developmental mutations, the researchers reckoned they would produce blind offspring. Instead, the experiment produced a number of fry with functioning eyes;..." This sounds like speculation--and no more--on their part.PaV
January 11, 2008
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Maybe we’re looking at this thing backwards. Could it be that the blind fish have finally provided an example of a complex system that is partially evolved? Maybe their vision system has been slowly evolving from scratch, and there is just one final mutation needed to complete the system! Let’s free a few million of those blind fish in a body of water outside the cave, and see how long it takes for that final mutation to occur, finally bringing sight to the previously sightless fish. Or is this just an evolutionist’s wishful thinking?Frank
January 11, 2008
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Re #13 Dave, thanks a lot for writing clear explanations that the average layperson can understand. It always bothers me when certain neo-Darwinists, especially biologists act as if one must be a trained biologists to understand this stuff. I am of the opinion that, if a scientist claims to understand a phenomenon but is unable to explain it in a simple language that the average layperson can understand, he/she has no clue as to the nature of the phenomenon. I think this is the best way to distinguish a con artist from an honest scientist. Again, thank you.Mapou
January 11, 2008
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dk So we concede that the lack of light would favor a fish which survives without eyes… or at least that perhaps some other trait is dominant that helps the blind ones survive in the dark better than the ones that have sight. Not at all. Or at least not a significant factor in this instance. Vision, or lack thereof, becomes irrelevant in the dark. Yes, if producing a functional eye takes up more resources than not producing a functional eye then that's something theoretically selectable but it would be a very slow process in that case. In this case the lack of any immediately significant fitness penalty due to blindness allows the vision system to rapidly decay. Selection works against increasing entropy. Take it away and entropy increases at a hugely accelerated pace. The $64,000 question is whether natural selection can completely overcome increasing genetic entropy. The Darwinian faithful believe it can. The rest of us are skeptical at best. I think John Sanford has the most readable and convincing treatment of this question in the book "Genetic Entropy". DaveScot
January 11, 2008
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Fish lose their eyesight in the dark far too quickly to be explained by progressive evolution through random mutation and natural selection. It's the absence of natural selection that explains it. Without natural selection acting as a conservative force random mutation runs rampant. Since random mutations are overwhelmingly deleterious the genes responsible for vision get ruined in a comparative eyeblink of time. If there was some other widely accepted explanation for it then that explanation must be quite dated. I don't think any competent biologist born in the last 100 years would entertain any explanation other than random mutation absent natural selection. DaveScot
January 11, 2008
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So we concede that the lack of light would favor a fish which survives without eyes... or at least that perhaps some other trait is dominant that helps the blind ones survive in the dark better than the ones that have sight. Conversely how do we know that the presence of light doesn't have some effect on the genes. The fish with better eyes survive, presumably because they use them to find food and avoid predators. What I am getting at is. Do we know if the genes that the fish carries can be effected while the fish is alive... Is a dominant trait that is there to begin with (at birth) all there is to work with?DK
January 11, 2008
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the theory that I remembered was that natural selection selected for blindness because an eye in such an environment would be more of a liability when damagedari-freedom
January 11, 2008
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ari-freedom I'm not quite sure what you mean to say. Natural selection is largely if not totally a conservative force. It works to maintain the status quo by killing off mutants that wander too far off the reservation. If vision is not required for anything then natural selection stops culling the mutants whose vision is compromised. It's very effective in this conservative role. Beneficial mutations are statistically rare and at best (with very rare exceptions like antibiotic resistance aquired through one or a few point mutations) only very slightly beneficial. On the other hand deleterious mutations are quite often so serious the organism dies long before it can reproduce and the great majority of the rest of the mutations are either neutral or very slightly deleterious. Because of this situation natural selection is ineffective at isolating and propagating any beneficial mutations. The beneficial mutations are overwhelmed by the accumulation of slightly deleterious mutations which occur so frequently. When a beneficial mutation occurs it must be accepted along with the deleterious mutations. Reproduction is an all or nothing process. Natural selection acts on the whole organism not individual pieces of it - it can't take the good without taking the bad at the same time. I recommend John Sanford's book "Genetic Entropy" for a more in depth treatment on this dilemma which IMO makes RM+NS incapable of long term progressive evolution. DaveScot
January 11, 2008
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DK The first is almost certainly correct - visioned fish would lose their eyesight if bred in the dark long enough. The second - would partially visioned fish constantly find improved vision if bred in the light - is questionable. Almost certainly they would if amongst the entire population a complete set of functional vision genes already existed. This would be akin to front loading - the potential is already there. If in the entire population there was not a complete set of functional genes for eyesight a neo-darwinist would say that RM+NS would eventually restore vision regardless of the state of disrepair whereas an IDist would likely say, dependent on the scope of the "repairs" necessary, RM+NS is not sufficient with any reasonably finite number of opportunities to effect progressive positive change. DaveScot
January 11, 2008
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I thought the blindness was a result of natural selection (since it was considered "beneficial" for a post hoc reason). Now you're saying this is an example of natural selection in action for everything else, since they don't change.ari-freedom
January 11, 2008
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If the 1/2 of the 40% that gained sight were isolated and bred in the dark would they lose sight again due to the lack of need for sight? If the other 1/2 of the 40% was bred in the light would their eyesight improve?DK
January 11, 2008
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