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Who needs night vision? When evolution means going blind


Becoming eyeless is an adaptation of sorts, no?

ScienceDaily (Sep. 15, 2010) – University of Maryland biologists have identified how changes in both behavior and genetics led to the evolution of the Mexican blind cavefish (Astyanax mexicanus) from its sighted, surface-dwelling ancestor. In research published in the August 12, 2010 online edition of the journal Current Biology, Professor William Jeffery, together with postdoctoral associates Masato Yoshizawa, and Å pela Goricki, and Assistant Professor Daphne Soares in the Department of Biology, provide new information that shows how behavioral and genetic traits coevolved to compensate for the loss of vision in cavefish and to help them find food in darkness.

This is the first time that a clear link has been identified between behavior, genetics, and evolution in Mexican blind cavefish, which are considered an excellent model for studying evolution.

Actually, to the extent that the cavefish lost a trait rather than gained one, what we are studying here is devolution rather than evolution. Just how the main different types of eye evolved is a fascinating topic. How traits can get lost is interesting too, but not as relevant to the question of how great gains in information really occur.

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There is no need to invoke evolution for how these fish changed. First nothing was witnessed and so its speculative. origin issues always are and so this is why every graduating class has hopes of overturning their textbooks and getting a prize. Yes simple adaptation mechanisms are hee and about but not from the unlikely origin of mutations going wrong but usefull.This cave fish thing is case in point. Always i have found that any fish that is around the caves will have relatives in the caves without eyes etc. It follows that losing them is from innate triggers and gaining any physical ability is from like triggers. In fact as a YEC person i see many cave creatures adapted this way since the ice age which by our timeline could only be since about 1600 B.C. . It must be instant. A experiment could be to take a pile of creatures and put them in a cave and come back every month and see how fast these changed. I say it would be instant and not from the death of all but a few with new physical traits from mutations after birth. The caves might show the light on all this. Robert Byers
CY, I think you've missunderstood part of the paper. The eyes cease functioning as soon as the fish move into the dark cave. No light = eyes don't work, even if they're still perfect. The fact that the eyes don't work in a dark environment sets them up for devolution. Surface fish have plenty of light and use their eyes. If a surface fish is born with a mutation that makes its eyes stop working, the fish will be eaten before it ever has a chance to mate and pass the bad gene along. In a dark cave, a fish with the same mutation doesn't notice a thing. Its eyes were already useless because of the lack of light. You can't evolve something to "fix" the eye because not even a perfect eye will work in the dark. If the eye was mysteriously fixed, and the fix started to spread throughout the population, it would be a sure sign that something was wrong with evolutionary theory. You don't need to wonder what would happen if the cave fish lost their sense of touch. Surface fish don't have it and they have no VAB response. As the article suggests, VAB is hazardous on the surface where large predators are ready to snatch a curious fish. The cave fish have larger hair cells than the surface fish and are presumably better at detecting the vibrations. They have no predators to eat them. We don't know that VAB will evolve into something more complex. We do know, from the laboratory experiments described in the paper, that VAB works better than no VAB right now. Most vibrations in cave water are made by something edible and VAB fish home in on those vibrations and consequently eat better than non-VAB fish. We also know the VAB behavior is caused by mutated DNA because of the cross-breeding experiments described in the paper. Surface fish have no VAB, cave fish have a full VAB and cross-breeds have an intermediate amount of VAB, exactly what you'd expect if the effect was genetic. warehuff
deric,adaptation is when your body adjust itself to function differently under changing conditions. For instance, there are several feedback loops in your body that adjust the numbers of red blood cells in your blood to efficiently carry oxygen to your cells. If you were born and raised at sea level, you will have enough red blood cells to extract oxygen from the dense sea level atmosphere and carry oxygen to your cells. If you then move to a 15,000 feet (3k meters) mountain top, you would have too few red blood cells to extract oxygen from the thin atmosphere and carry it to your cells. You'd be dizzy, you'd tire easily, you might pass out occasionally, you might even die if you were in bad health beforehand. But as soon as you get to the mountain top, your body notes the oxygen deficiency in your blood and tells your blood marrow to start manufacturing more red blood cells. After a few days, those extra cells let you breathe more easily and after a few weeks or months you've got so many extra red cells in your blood that you're almost back to normal. That's adaptation. The body changes, but the DNA stays the same. Meanwhile, people who have been living at high altitudes for many generations are born with more red blood cells and as adults, their blood has more red cells in it than yours does, even after you've fully adapted. That's because some of their ancestors were born with mutations to their DNA that caused their bone marrow to make more blood cells right from the start and they've probably had a few more mutations that make their blood marrow more efficient at making red cells. Those people did better at high altitudes and more of their children survived and passed the mutated DNA on. This is evolution - changes to the DNA that cause an organism to work differently. Adaptation = no changes to DNA. Evolution = changes to DNA. warehuff
deric, Warehuf, "What is the difference between adaptation and evolution? Is there a difference?" (This is my understanding, so bear with any incongruencies.) I would say yes and no. You can't adapt without changing something you're adapting to, and evolution means change. But not all adaptations mean that something novel has emerged or even that biological evolution has occurred. Behavioral adaptations, for example are not necessarily an example of biological adaptation. So adaptation is essentially what evolution is, but not all adaptations are evidence of evolution in the sense of developing new novel features, and I think we can all agree on that. I think the issue here is not that there isn't any evolution. Certainly the eye in the blind fish has changed. The issue is whether such changes actually lead to new novel features, which are more complex and functional than the last, as Darwinian evolutionary theory suggests. We can't prove that the behavioral changes are a result of a biological increase in novelty. We can only say that the behavioral changes are a result of a biological decrease in novelty in this case. Natural selection suggests in this instance that when there's a loss of sight, what Warehuf mentions, "VAB" emerges as an adaptation in order for cave fish to still "see" in the dark. Fair enough, and I don't think anyone would dispute that this is what occurred. But how did it occur is the big question. These and other such changes often lead the Darwinist to assume and predict that there will be further novel changes, which will lead to more complex and functional features. And that's exactly what is assumed here, but isn't what has apparently occurred; quite the opposite. Warehuf thinks that O'Leary's assessment of devolution is not what occurred, but it clearly is. Why adapt to the loss of sight with something else entirely if the eye no longer functions as it once did? Furthermore, by what evidence do we assess that this new "VAB" will emerge into something more complex, functional and novel? Could the fish simply have changed their behavior as a result of a loss, and any further improvement in VAB is the result of their improving the behavior? You still have the eye, why not rather evolve a system that fixes the non-functioning eye and makes it more complex to compensate for such losses as ToE suggests? That would truly be evidence for ToE, and what we would expect, but then again, how would we know that this is what occurred? I think the next step here is for these fish to lose their sense of touch, such that they can't feel the vibrations in the water, which allow them to sense a water disturbance. That's what I would expect if the loss of sight is any indication. The behavior issue in the article assumes that the VAB developed as a result of the loss of sight. This is also a fair assessment: however, blind people use echolocation. Does this mean that they evolved a new novel feature, which allows them to "see?" I would be begging the question if I said "Yes." It more clearly and simply means that they determined to use what was already in them to distinguish certain distances so they don't run into walls as they walk - IOW, they adapted to a situation wherein their eyes don't function as intended. Adaptation may mean evolution, but it doesn't necessarily mean that something biologically novel emerges that isn't already there. Adaptation can be a behavior change, as the article points out. But you can't extrapolate by this that what we see in more complex eyes, such as the human eye is a result of this type of apparent behavioral adaptation. Far from it. CannuckianYankee
What is the difference between adaptation and evolution? Is there a difference? deric davidson
If "evolution" means losing, as opposed to gaining, complex traits like vision, then we shall find plenty of examples.
Evolution is about adaptation to environments, involving loss, gain or alteration. This fish apparently provides an example of two of these---losing sight (costly to maintain) and altering responses to vibrations to suit life in a dark cave, as warehuff noted.
The quest is to discover the true source of huge gains in compex information, and Darwinism is simply an imposture, impeding discovery.
I agree that these fish ultimately point to an intelligent source. However, Darwinism provides a mode of interim reasoning which is appropriate to these instances. It certainly isn't an "imposture, impeding discovery". equinoxe
Warehuff, if "evolution" means losing, as opposed to gaining, complex traits like vision, then we shall find plenty of examples. The quest is to discover the true source of huge gains in compex information, and Darwinism is simply an imposture, impeding discovery. O'Leary
The study's not about how the cavefish lost their vision, the study "... shows how behavioral and genetic traits coevolved to compensate for the loss of vision in cavefish and to help them find food in darkness." If you follow your link, the study shows how "'Vibration Attraction Behavior' (or VAB) is the ability of fish to swim toward the source of a water disturbance in darkness. ... Most cavefish displayed VAB and would swim toward the vibrating rod and poke at it, while few surface fish did. This behavior is advantageous for feeding success in the dark caves where food sources are limited and large predators are absent. 'Outside the cave, however, there are many predators,' explains Jeffery, 'and indiscriminately going to a vibration would be a certain risk for predation for a surface-dwelling fish.'" It further shows that cave-dwelling fish have more and larger sensory hairs that are essential for locating vibrations and that genes control their size and number. It's an evolution story about building better hunting behavior, it doesn't concern the devolution of the eyes at all. warehuff

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