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Author Topic:   Is Evolution Reversible
doc
Junior Member (Idle past 5420 days)
Posts: 11
Joined: 05-17-2009


Message 1 of 49 (508976)
05-17-2009 7:08 PM


The local variation in a population is reversible (micro-evolution) but is macro-evolution reversible? Obviously not exactly but if conditions changed then would evolution back-track?
Evolution doesn't have a direction so surely it is possible for it to go backwards?

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Admin
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Message 2 of 49 (509050)
05-18-2009 8:40 AM
Reply to: Message 1 by doc
05-17-2009 7:08 PM


You just joined and proposed three topics. I'll promote one (Is Evolution Reversible) and close the other two (Human Evolution and Evolution of the Eye). If things go well with the promoted topic then feel free to repropose the ones I closed sometime down the road.

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Message 3 of 49 (509051)
05-18-2009 8:40 AM


Thread moved here from the Proposed New Topics forum.

  
Coragyps
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Message 4 of 49 (509055)
05-18-2009 9:33 AM
Reply to: Message 1 by doc
05-17-2009 7:08 PM


Hi, doc! Welcome!
Evolution could perhaps be "reversible," but the chances of random mutation and natural selection getting you back to where you started would be exceedingly slim....

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bluescat48
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Message 5 of 49 (509056)
05-18-2009 9:50 AM
Reply to: Message 1 by doc
05-17-2009 7:08 PM


Evolution doesn't have a direction so surely it is possible for it to go backwards
You have sort of answered your own question except there is no forward or backward. In some senses it would appear that the evolution is directional but the traits only appear when such traits are positive to the species otherwise the trait is usually lost or significantly reduced. One example of such is the excretion of Nitrogeneous wastes among vertebrates. Bony Fish by ammonia, cartiligeous fish by urea, Amphibians start with ammonia then as adults by urea, reptiles & birds start as ammonia , go to urea and finally while still in the embryonic stage to uric acid, this is the same for the monotreme mammals but the placentals revert back to urea.
Although there is some uric acid formed, it is a very small amount and all placentals except the anthropoid apes (monkeys, apes to include humans), convert the uric acid to allantoin but the anthropoids don't. Since there is no way for the kidneys to excrete uric acid, it would seem that it is a regression for the anthropoids to not convert the uric acid to allantoin.

There is no better love between 2 people than mutual respect for each other WT Young, 2002
Who gave anyone the authority to call me an authority on anything. WT Young, 1969
Since Evolution is only ~90% correct it should be thrown out and replaced by Creation which has even a lower % of correctness. W T Young, 2008

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Dr Jack
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Message 6 of 49 (509057)
05-18-2009 9:52 AM
Reply to: Message 1 by doc
05-17-2009 7:08 PM


It depends what you mean by reversible, really. One could make an argument that snakes, sea cucumbers and dolphins represent evolutionary reversals, for example.

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doc
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Posts: 11
Joined: 05-17-2009


Message 7 of 49 (509059)
05-18-2009 9:57 AM
Reply to: Message 4 by Coragyps
05-18-2009 9:33 AM


Yes I understand that it would be almost impossible (but not impossible) to retrace exactly.
However my question is really asking "are the previous versions lost or are they still possible". It should be easier to loose "advantages" rather than to gain them.
Microevolution is "reversible" but how far back can it go?
Ok so I know some people will say that evolution always goes forwards (like time) which is true but I'm asking if conditions changed then would the path be retraced if that gave a benefit. It would be "easier" to do this than to find a different solution (if an old solution worked then use it).

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Perdition
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Posts: 1593
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Message 8 of 49 (509092)
05-18-2009 5:17 PM
Reply to: Message 7 by doc
05-18-2009 9:57 AM


It is theoretically possible, but highly unlikely that due to changing conditions, a species would revert to an ancestor species. More likely would be a new set of mutations that may end up with a similar looking species, or a species that has similar capabilities, but if you were to do an actual genetic sequence, it wouldn't match the progenitor that it now resembles again.

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RAZD
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Posts: 20714
From: the other end of the sidewalk
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Message 9 of 49 (509114)
05-18-2009 6:30 PM
Reply to: Message 7 by doc
05-18-2009 9:57 AM


Hi doc, and welcome to the fray.
It should be easier to loose "advantages" rather than to gain them.
Only if they lose their advantage, otherwise selection will continue to favor them. Conditions can change, such that advantage and disadvantage oscillate with ecological conditions, especially ones that fluctuate in a cyclic manner over cycle times greater than generation times. Here's an example of this kind of thing happening:
Newsroom - The Source - Washington University in St. Louis
quote:
Walking sticks regained flight after 50 million years of winglessness
Maxwell and his collaborators at Brigham Young University discovered that some species lost the ability to fly at one point of their evolution and then re-evolved it 50 million years later.
And it is not just ONE such instance, but several. See Figure 1 from Nature 421, 264 - 267 (16 January 2003); doi:10.1038/nature01313 (reproduced below)
Walkingstick insects originally started out as wingless insects (blue at start and top row). That diversified.
And some of them gained wings (red). And diversified.
And some of them lost wings (blue again). And diversified.
And one of those gained wings again (Lapaphus parakensis, below, red again).
Is that what you are looking for?
Microevolution is "reversible" but how far back can it go?
As long as the mutations are retained in the population, then the variation in frequency of alleles by natural selection can favor one set of alleles in one condition and another set of alleles in a second condition, so it is entirely possible for the population to shift back and forth between existing and available variations in an oscillating ecology. An easy example of just this happening is the peppered moth, as described on Peppered Moths and Natural Selection, where we have two varieties of the moth:
  • Biston betularia typica (the light color version) and
  • Biston betularia carbonaria (the dark color version)
    B.b.typica was the predominant variety before the industrial revolution, during the industrial revolution's dirtiest times the proportions of the two populations shifted so that B.b.caronaria became the predominant form. Then the industries cleaned up and B.b.typica returned as the predominant variety.
    This does represent the change in hereditary traits in populations from generation to generation -- evolution in it's basic form, and what is usually meant by "microevolution" by biologists and creationists (something they agree on???).
    Message 1
    ... but is macro-evolution reversible?
    This depends on what you mean by "macro-evolution" and what you mean by reverse.
    As Mr. Jack noted dolphins are mammals that have become fish-like. They have "reversed" to a marine organism from a land organism.
    But if you mean "macro-evolution" as the division of species into multiple species (speciation) and then the development of relationship groups -- genera, families, etc -- the reversal of divisions of species into different categories of species (what biologists mean by "macro-evolution"), then no, that will never happen. Once the division of a parent species into reproductively isolated daughter populations has occurred that division cannot be undone.
    Enjoy.

    we are limited in our ability to understand
    by our ability to understand
    Rebel American Zen Deist
    ... to learn ... to think ... to live ... to laugh ...
    to share.


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  • This message is a reply to:
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    pandion
    Member (Idle past 3000 days)
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    Joined: 04-06-2009


    Message 10 of 49 (509142)
    05-19-2009 1:04 AM
    Reply to: Message 9 by RAZD
    05-18-2009 6:30 PM


    Richard Dawkins does a quite nice discussion of the question in his book, Climbing Mount Improbable. The answer is the organisms that are highly adapted to a limited environment will go extinct when that environment changes suddenly.

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    Dr Adequate
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    Message 11 of 49 (509143)
    05-19-2009 1:23 AM
    Reply to: Message 1 by doc
    05-17-2009 7:08 PM


    It would often be qute hard for evolution to go back the way it came.
    It is true that for any series of mutations that will get you from A to B, there's an exactly opposite set of mutations that will get you from B back to A. But then there's natural selection to be taken into account.
    Consider birds for example. They evolved from things that couldn't fly into things that could fly, into things that could fly really well --- and then some of them evolved to be flightless. Now, you might call that last step "evolution going backwards" in a loose sense, but it cannot go back the way it came.
    For flightless birds evolve when the benefits of being large outweigh the disadvantage of being too large to fly, and this natural selection permits. But for evolution to go back the way it came, flighted birds would have to evolve to a flightless form via an intermediate stage like Archaeopteryx. But this would require them to evolve from birds that fly to birds that still fly but not so well. And this natural selection will not permit.
    ---
    An interesting example of a similar phenomenon can be seen today in the laboratory. If you infect a culture of single-celled Chlorella algae with single-celled flagellate predators, then the algae evolve into a colonial form which is too big to eat. The way in which they do this is interesting.
    The first step is a mutation which makes the normal process of cell division incomplete. The result is that they go straight from single-celled organisms to colonial organisms consisting of hundreds of cells. While this is favored by natural selection, it has its drawbacks: most obviously, the cells on the inside are going to be deprived of nutrients.
    So what happens next is that selection favors progressively smaller and smaller colonies until it reaches a stable form of eight cells, all of which are at least partly on the outside of the organism: this ameliorates the nutrient problem but is still too large to be eaten.
    Now, what do you suppose happens when you take the predators away again? Does evolution go back the way it came? No: it can't. For to do that, the colonies would have to get bigger and bigger, which would exacerbate the nutrient problem but carries no benefits whatsoever, so natural selection will not permit evolution in this direction. And indeed experimenters observe that the eight-celled form remains stable in the absence of predators.
    Edited by Dr Adequate, : No reason given.

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    bluegenes
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    Message 12 of 49 (509161)
    05-19-2009 3:20 AM
    Reply to: Message 1 by doc
    05-17-2009 7:08 PM


    doc writes:
    Evolution doesn't have a direction so surely it is possible for it to go backwards?
    Only on a very "micro-micro" level is evolution likely to reverse exactly. Here's some research which shows that an apparent reversal, or near reversal, in phenotype may only be a ~50% reversal in genotype. In other words, after a certain point, there's no real going backwards on history at the genetic level even though some individual mutations can be reversed.
    The experiment described here is still well within the bounds of what we would describe as micro-evolution.
    http://www.sciencedaily.com/...ases/2009/01/090111163023.htm
    The paper's here for those with access to Nature Genetics.
    Experimental evolution reveals natural selection on standing genetic variation | Nature Genetics

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    doc
    Junior Member (Idle past 5420 days)
    Posts: 11
    Joined: 05-17-2009


    Message 13 of 49 (509179)
    05-19-2009 6:07 AM
    Reply to: Message 9 by RAZD
    05-18-2009 6:30 PM


    RAZD:
    Walking sticks regained flight after 50 million years of winglessness
    Maxwell and his collaborators at Brigham Young University discovered that some species lost the ability to fly at one point of their evolution and then re-evolved it 50 million years later.
    And it is not just ONE such instance, but several.
    Walkingstick insects originally started out as wingless insects (blue at start and top row). That diversified.
    And some of them gained wings (red). And diversified.
    And some of them lost wings (blue again). And diversified.
    And one of those gained wings again (Lapaphus parakensis, below, red again).
    Is that what you are looking for?
    Yes it's a good example.
    Ok let me see if I can explain this.
    Looking at your diagram......
    You said that they started of at the top left as wingless.....however it appears that they started as winged and "immediately" lost their wings. The first winged version appears to be in existence today (top right).
    From your text it seems that the loss of wings occurred over 50 million years ago.
    It appears to me that those versions that regained their wings were not evolving wings but were "switching" them back on.
    I think there's one example in the diagram where they then lost the wings again after regaining them.
    Loosing wings is not just as simple as first would seem (the interfaces at the wing root need to change).
    So it looks to me like there were two options available right from the start of your diagram.........wings and wingless. These options carried on right to today and at different stages the options were turned on (I don't think wings or wingless re-evolved).
    Hence it looks like the options remained for 50 million years.
    So what I'm saying is that even after 50 million years it is possible to "backtrack". I don't think that any of the changes (winged to wingless) was a new evolution but rather a switching on of two mutually exclusive options. I think if the wings or wingless options had to re-evolve then they would have been significantly different to anything that had been in existence before (is evolution repeatable....I don't think so).
    I guess that asks the question........how much is "mutation" and how much of what we see is switching on or off of options?

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    RAZD
    Member (Idle past 1405 days)
    Posts: 20714
    From: the other end of the sidewalk
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    Message 14 of 49 (509262)
    05-19-2009 8:17 PM
    Reply to: Message 13 by doc
    05-19-2009 6:07 AM


    Hi doc,
    The first winged version appears to be in existence today (top right).
    All of the species and the right side of the diagram are in existence today, but what the diagram does not show you is whether there was what would be called "orbitrary speciation" along any of those legs. What you see are the speciation divisions of populations and the final results 50k 50 million years later. Thus the top line could be just as recently evolved as the others, just that all the mommy and daddy species were wingless.
    These options carried on right to today and at different stages the options were turned on (I don't think wings or wingless re-evolved).
    Ah, but "wing" or "wingless" is not necessarily a single gene, nor is just a matter of turning it on or off. What we are likely seeing is the loss and re-evolution of parts of the whole wing formation process. This process may in fact be broken in different places for different species.
    You can turn a feature off by blocking or removing any part of the development critical to the formation of wings, and this would likely leave you with the same original feature that the wings evolved from, plus some genes inherited while winged that are not removed. Thus if a new by-pass is evolved to get around the blocked or removed part it would allow necessarily similar wings to evolve - it would be preadapted to form similar wings.
    This would be similar to the "Irreducible Complexity" refuting experiment done with E.coli (see Ken Miller "A True Acid Test") where an element crucial to the metabolism of lactose was removed from a subsystem, and a new set of elements evolved to replace the broken subsystem allowing the whole metabolism system to function again.
    I think if the wings or wingless options had to re-evolve then they would have been significantly different to anything that had been in existence before (is evolution repeatable....I don't think so).
    How much is "significantly different"?
    Would it not still be working from the same basic features that were there when the wings first evolved? If I remove a sprinkler from the end of my hose I am still capable of watering the lawn, and I can put another sprinkler on the same hose.
    If a bat lost the bat wing, would it not still have a hand\paw with finger bones that can evolve back to support a skin membrane?
    Is the membrane pattern of the colugo significantly different from a bat?
    Does not convergent evolution answer this question best then?
    If a possum and a squirrel can evolve into such similar critters from widely divergent backgrounds and many eons from a common ancestor, then is it not possible that the same ecological niche can drive evolution to repeat a similar solution?
    how much is "mutation" and how much of what we see is switching on or off of options?
    The switching on and off -- if that is indeed what was happening -- is still caused by mutations, so all of it is mutations.
    Enjoy.
    Edited by RAZD, : correction

    we are limited in our ability to understand
    by our ability to understand
    Rebel American Zen Deist
    ... to learn ... to think ... to live ... to laugh ...
    to share.


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    This message is a reply to:
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    dwise1
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    Message 15 of 49 (509276)
    05-20-2009 1:52 AM
    Reply to: Message 9 by RAZD
    05-18-2009 6:30 PM


    As Mr. Jack noted dolphins are mammals that have become fish-like. They have "reversed" to a marine organism from a land organism.
    OK, let's take a closer look at this, which might clear a few things up.
    In the case of the peppered moths, the coloration traits have not yet resulted in speciation, so the population can shift from a predominance of one trait or the other.
    But in the case of dolphins, speciation has occurred. The question of whether evolution is reversible asks whether evolution will follow the same path back. The answer is obviously, "No". In reality, a species always starts from where it currently is.
    In the case of dolphins, they are describe as having become "fish-like", when actually they are only superficially so. Their general shape is "fish-like", but that's as far as it goes. Fish swim by moving their body and rear fins side-to-side. How does a dolphin (ie, a porpoise, not a mahi-mahi) swim? By moving its flukes up and down. A porpoise's mode of swimming is very different from a fish's. Human divers even make use of the "dolphin kick", something that is natural for certain mammals but not for fish.
    Does a porpoise have gills? Uh, no! It has lungs, as do all cetateans. Is a porpoise cold-blooded? No. Is a porpoise a fish? Frak no! It's still a mammal!
    In this case, evolution has not reversed itself. Mammals had to re-evolve fish-like qualities solely because of the environment, but all of those qualities are based on where their ancestors had started from.
    Edited by dwise1, : No reason given.

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