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Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
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Author | Topic: “Rapid Evolution” Method Found in Eyeless Fish | ||||||||||||||||||||||||||||||||||
Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
I'm active in debates about evolution vs creation in forums in my own language, and while most of creationist arguments there are pretty much standard, there was an intriguing one recently.
We were presented with this picture of small fish A. Mexicanus tetra, which is able to switch from normal appearance to cave-adapted in few generations. It is argued by creationists that such cases prove that evolution is not able to make big changes and adaptations, and all information is already included in genome; the phenotype just switches as required.
Source here: http://www.biosciencetechnology.com/...od-found-eyeless-fish So, what to think of it? It's just some regulatory genes switching on and off so that endangered species might change forms? We would expect that over many generations natural selection favors pale fishes with smaller eyes, but this is not the case. Evo-devo might give some explanations; it is known that some changes in body forms (from leg to fin for example) are not beacuse genes mutated randomly; infact genes stay the same; it's gene expression that changes. This is why human babies might be born with tail and horses with more digits; genes are still in us, it's just genes for tail that are supressed. So, is it possible that this fish gradually evolved to cave-like fenotype while still retaining all genes for "normal" version? Basically it evolved the machanism to switch back and forth? It would be very benefitial for those who are living in borderline zone between light and dark.This sounds a bit like ad-hoc explanation, so I'd like to hear other opinions, possibly from experts. This could go in biological evolution. Edited by Bojan, : some typos
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
quote: Well, the article doesn't say, but it seems like it's within few generations, or less. The general mechanism is by blocking protein HSP90 (whatever that is) artificialy by cemichals, or naturaly because of decreased light and cold (basicaly cave conditions).
quote: Of course, and we all know that creationists approach all "problems" by trying to discredit one example and then, somehow, all evolution is disproved. They do it by mentionig Nebrasca man, so all fossils are fake, they mention 1 case of stalagmite growing fast, so all of them probably grew within 6000 years, and so on. This is why I'm interesting in this particular case, I'm curious about most likely evolutionary mechanism which explains how such ability (to switch between forms) evolved.
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
Nitpick: Evolution doesn't "know" whether a species is endangered or not. It can't anticipate that the environment will change back and forth. All it can do is react to changes after they happen. If a switching mechanism does exist, it must have evolved in the "conventional" way. So what would that way be? If we look some examples in nature, it's obvious that changes in phenotype don't happen in a way that previous versions are "erased" in genome. Humans sometimes are born with tails, dolphins get back legs and so on. Atavisms are evidence that the general "blueprint" for a limb, for example, is preserved, and change in form is because of different gene expression / regulation.There was an article recently about a mutant chick embryo which got a reptile snout after researchers tampered with gene regulation. So, is this the evolutionary mechanism? Animal slowly evolves different form through changes in gene regulation, while also retaining the ability to switch back quickly through epigenetics?
Epigenetics is the study of changes in gene expression caused by certain base pairs in DNA, or RNA, being "turned off" or "turned on" again, through chemical reactions.
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
Looking at "some" examples seems to be the problem here. If some species can switch back to an earlier phenotype (or switch back and forth), we still can't conclude that all evolution works that way. It isn't enough evidence to suggest that the general blueprint is preserved in perpetuity. There is this remarkable experiment with mouse eye genes inserted into genome of a fly and that caused additonal eyes growing on the tip of the antennas. Since the genes from a mouse produced eyes of a fly, that shows that some basic general blueprint is preserved through vast time and many species. Last common ancestor between flies and mice was probably in cambrian.Why did mouse genes produce fly eyes? Because there is this additional layer of gene control with some parts of DNA promoting and suppressing genes.
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
I think that the OP title "Rapid Evolution" is possibly a misnomer insofar as what constitutes rapid in evolutionary time spans. I agree, "rapid evolution" is taken from the title of the article. These changes are obviously not evolution.
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined:
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Note that humans exhibit neotony as well ... that is one of the reasons humans appear hairless compared to apes, the vellus hair (short, light\blond) is retained (especially in women) rather than being replaced by mature hair (longer, darker), and also why the human skull is 'frozen' in a juvenile form compared to other apes. Certainly eyes are part of the development in a mature fish, but are not fully formed in early fetal development. This is interesting, and changes in that fish sure looks like neoteny. No pigments and suppressed eye development. Otherwise it would be fatal, except in caves where it becames useful mutation. Now, I'm curious, are all animals able to switch to cave-like appearence quickly, or most of them evolved slowly? There is this rare and curious creature, endemic amphibian from a cave in Slovenia. His genome might be really interesting, perhaps it could be possible to somehow stop this development and maybe produce some salamander with color and eyes? However it's endagered and protected so I doubt breeding and experimenting is allowed.
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
A few or less? Hmm, if I remember my approximate math, few - less = not very many, and certainly < quite a lot. This is not as quantitative as I'd like. It seems hard to analyze the situation when the numbers are so vague. Whatever the number is, 1 or 5, it doesn't really matter. It's way to short to call it evolution. The transformation itself happens quickly, so the question is not if the fish is evolving from normal to cave-like. It's not. Question is how the whole mechanism of beeing able to switch evolved. Some examples here are really interesting, like neoteny.So, could this be one of possible models for evolution of such mechanism: some fish or salamanders could have some mutations which suppreses development in early stages. This could be beneficial for populations who live near caves and occasionaly end deeper inside. Then natural selection could favor those who can be easily triggered with enviromental factors related with cave conditions (cold, dark, certain chemicals).
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Bojan Junior Member (Idle past 3306 days) Posts: 9 From: Croatia, Europe Joined: |
Are you talking about this: Master Eye Gene Identified Yes, thank you very much. I was reading about it in various books, but this is much more detailed.
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