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Author Topic:   Is Evolution Reversible
doc
Junior Member (Idle past 5419 days)
Posts: 11
Joined: 05-17-2009


Message 31 of 49 (509992)
05-26-2009 3:01 PM
Reply to: Message 30 by Perdition
05-26-2009 2:48 PM


Perdition writes:
Who said it's the same solution? Just because they look similar doesn't mean they are duplicates. Evolution, and natural selection in particular, are still constrained by the laws of physics. If selection is moving towards a flying model, the ultimate "design" is going to necessarily resemble the original flying model despite having, perhaps, an entirely different set of genes creating the apparatus.
How does selection determine a flying model?
Evolution does not have any "knowledge" and hence even if a "flying model" was better, evolution couldn't end up with an almost identical result through random mutation.

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 Message 30 by Perdition, posted 05-26-2009 2:48 PM Perdition has replied

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Perdition
Member (Idle past 3237 days)
Posts: 1593
From: Wisconsin
Joined: 05-15-2003


Message 32 of 49 (509995)
05-26-2009 3:21 PM
Reply to: Message 31 by doc
05-26-2009 3:01 PM


Evolution does not have any "knowledge" and hence even if a "flying model" was better, evolution couldn't end up with an almost identical result through random mutation.
It depends on the environment and the population size. If you have a small number of individuals, then yes, the chance of it evolving is lower than if there are a large number of individuals. Assuming the environment is such that flying is better than not flying, from a reproductive success standpoint, and the basic bodyplan of the individual already comes with the necessary precursor apparatus, then any mutation would have to build on what is already there, and so will probably end up with something similar.
It is entirely possible, depending on the number of changes since the original flying type, for an exactly opposite mutation to occur, resulting in a wing that is genetically identical to the original, but it is more likely that a merely similar one would arise.
Edited by Perdition, : No reason given.

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dwise1
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Posts: 5930
Joined: 05-02-2006
Member Rating: 5.8


Message 33 of 49 (509999)
05-26-2009 3:50 PM
Reply to: Message 25 by doc
05-25-2009 5:28 PM


Perhaps part of the confusion is due to a lack of definition: what exactly would constitute a reversal of evolution? IOW, do you even know what you're asking?
RAZD writes:
That the vein patterns in the wings are the same means that the vein pattern is not lost, ... but then this is the vein pattern in the part when it is NOT a wing as well as when it IS a wing. But the question remains: if the wing is turned OFF by one mutation, and then later is turned ON, then is this a new mutation of a new ON switch, or is this a new mutation that reverses the mutation that turns the wing OFF? It is entirely possible that both could occur.
I think it's more probable that the information is not lost and hence in this case evolution can reverse something that was done millions of years ago.
Did you understand waht RAZD was describing? Do you have any idea where that information resides? And just how is the retention of that information supposed to indicate evolutionary reversal? The conclusion you reached seems contrary to the premises.
Are you familiar with basic genetics? Familiar with what the genotype and phenotype are and how they related? Furthermore, do you understand about genotypes and phenotypes and how they fit into evolutionary theory? If you do not, then no wonder you're confused.
The phenotype is that set of characteristics that the physical body has. It gets those characteristics from the genotype, which is that individual's set of genes. It is the genotype that contains the genetic information for the expression of physical characteristics in the phenotype. Note, please, that said information may or may not be expressed; there are specific DNA sequences that will switch genes on or off.
Thus, the information can exist in the genotype, but never get expressed in the phenotype. Like hens' teeth. Do chickens have teeth? No, but the dinosaur-bird transition, represented by Archaeopteryx, did. Bird "lost" their teeth ... or did they? In experiments in which mouse-embryo gum tissue is placed onto chick embryo jaws, those jaws develop tooth buds. Thus we see that chickens' genotypes still contain the genes for teeth, but those genes are normally never expressed and thus never appear in their phenotypes.
Now, how do genotypes and phenotypes fit in evolutionary theory? What the phenotype is like depends directly on the expression of the genotype. All variability lies in the genotype -- while that variability can result in variation among the population's phenotypes, it is still the variations within the genotypes that is of significance, which is one reason why we call it genetic variation. All mutations that have any evolutionary significance occur solely in the genotype and specifically in the genes of the germ cells (ie, sperm, eggs) and not in the body cells; only those genetic changes that can be inherited could ever be of any evolutionary interest. All recombination through reproduction also happens solely on the genetic level, in constructing a new genotype.
The only real role the phenotype has is that selection doesn't act upon the genotype directly, but rather indirectly through the phenotype. The different phenotypes get selected for or against and so indirectly their genotypes get selected. It's a very results-oriented process.
So, how do we measure whether evolution has been reversed? Just by looking at the phenotype? No, because come traits can be switched on or off with minimal changes in the genotype. I would vote for the genotype, since that is where the information actually lies. For evolution to reverse, all the genetic information for the trait in question would need to have been removed from the genotype. As I understand, that very rarely happens; rather, those genes are either switched off or damaged a mutation or by a ERV -- eg, we and other apes cannot produce our own vitamin C because that gene was destroyed by the same identical ERV, so we need to get it from our diet.
Another scenario is that a different genotypical pathway gets followed to "reverse" evolution -- eg, cetaceans having evolved from land mammals to become aquatic and "fish-like". But whereas it may superficially appear that evolution has been reversed, in reality a lot of new changes have been made to the genotype. The true test of whether evolution has been reversed is to compare the genotypes: only if the genotype has reverted to the earlier form can we even begin to suggest that evolution has been reversed.
Just in case you couldn't follow that, let me offer an analogy. Progressive dances proceed around the floor counter-clockwise along the "line of dance" (LOD). You enter the floor with your partner and start to dance down the LOD. A number of times you will pass by that point at which you had started. Now, have you reversed your dance? Sure, there are a few points where you had momentarily moved backwards, but you can ill afford to do that too much nor for too great a distance for risk of the other dancers crashing into you (country two-step is a particularly good example if this, since even slowing down can cause you be be run over and, let's face it, red-necks don't brake for nobody). Reversing your dance would require you to proceed against the LOD (ALOD). But didn't you instead proceed and progress ever forward in order to arrive at your starting point?

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Taq
Member
Posts: 9970
Joined: 03-06-2009
Member Rating: 5.6


Message 34 of 49 (510015)
05-26-2009 6:52 PM
Reply to: Message 18 by doc
05-24-2009 11:40 AM


doc writes:
Language "evolution" and the evolution of living things is not the same and it's not really a valid comparison.
I was trying to use language as an analogy. Languages do accumulate changes in an analogous manner to genomes. These language changes occur at the population level, much like evolution. We also see languages diverging, again very much like biological lineages. There are many parallels which makes the evolution of languages a good analogy (but an analogy only).
As I said before, none of the Romance languages are evolving in reverse. None are sounding more and more like Latin. In the same way, genomes do not evolve so that the sequence of DNA becomes more and more like it's ancestors. There is not a DNA memory that forces genomes to move towards a specific DNA sequence in response to an external stimulus. In the same way, there is nothing forcing Italian and French to move towards Latin.
Selection occurs at the phenotypic level, not at the genomic level. That is the lesson to learn here. Natural selection affects the results of DNA alteration, but it does not select for specific DNA changes. Also, natural selection is not searching for a specific solution. Natural selection is searching for higher fitness, no matter how it is achieved.

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Hyroglyphx
Inactive Member


Message 35 of 49 (511123)
06-06-2009 9:50 AM
Reply to: Message 1 by doc
05-17-2009 7:08 PM


Answer is in the question
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?
Didn't you just answer your question? If evolution doesn't have a direction, then going backwards is a contradiction in terms, as "backwards" is indicative of being directional.
If evolution simply means, "change," then there is no forward or backwards, just different.
If you are asking if humans can somehow devolve back in to single-celled organelles, I would think not.

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 Message 36 by Dr Adequate, posted 06-06-2009 8:26 PM Hyroglyphx has not replied
 Message 37 by Percy, posted 06-07-2009 5:56 AM Hyroglyphx has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 36 of 49 (511150)
06-06-2009 8:26 PM
Reply to: Message 35 by Hyroglyphx
06-06-2009 9:50 AM


Re: Answer is in the question
Didn't you just answer your question? If evolution doesn't have a direction, then going backwards is a contradiction in terms, as "backwards" is indicative of being directional.
I think that you, too, are misunderstanding the question.
By "evolution has no direction", he means that there is no innate tendency in in evolution to produce increased size or complexity or what-have-you.
So if some lineage got larger, than smaller, the period over which it got smaller would be "evolution going backwards".

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Percy
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Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 37 of 49 (511159)
06-07-2009 5:56 AM
Reply to: Message 35 by Hyroglyphx
06-06-2009 9:50 AM


Re: Answer is in the question
Just asking the question, "Is evolution reversible?" reflects Doc's muddled understanding of evolution, but Dr Adequate probably captures the sense in which Doc intended the question. Probably Doc would consider the recently documented evolution of finches in the Galapagos as an affirmative, though completely unspectacular, answer to his question.
The question can also be addressed at the genetic level. The simplest mutation of a single nucleotide substitution can certainly be easily reversed in the next generation. Other types of mutations would have their own particular probability of reversal. A chromosome duplication could easily be reversed a generation later, but a chromosome loss would be almost impossible to reverse (except in cases where it was a duplicate of another chromosome).
--Percy

This message is a reply to:
 Message 35 by Hyroglyphx, posted 06-06-2009 9:50 AM Hyroglyphx has replied

Replies to this message:
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Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 38 of 49 (511164)
06-07-2009 7:20 AM
Reply to: Message 37 by Percy
06-07-2009 5:56 AM


Re: Answer is in the question
A chromosome duplication could easily be reversed a generation later, but a chromosome loss would be almost impossible to reverse (except in cases where it was a duplicate of another chromosome).
A chromosome loss would be almost impossible to survive unless it was a duplicate of another chromosome.

This message is a reply to:
 Message 37 by Percy, posted 06-07-2009 5:56 AM Percy has replied

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 Message 39 by Percy, posted 06-07-2009 7:46 AM Dr Adequate has not replied
 Message 46 by Dr Jack, posted 06-10-2009 5:53 AM Dr Adequate has replied

  
Percy
Member
Posts: 22388
From: New Hampshire
Joined: 12-23-2000
Member Rating: 5.2


Message 39 of 49 (511166)
06-07-2009 7:46 AM
Reply to: Message 38 by Dr Adequate
06-07-2009 7:20 AM


Re: Answer is in the question
I was thinking plants when I considered whether that possibility was worth including.
--Percy

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Hyroglyphx
Inactive Member


Message 40 of 49 (511168)
06-07-2009 7:57 AM
Reply to: Message 37 by Percy
06-07-2009 5:56 AM


Re: Answer is in the question
The question can also be addressed at the genetic level. The simplest mutation of a single nucleotide substitution can certainly be easily reversed in the next generation. Other types of mutations would have their own particular probability of reversal. A chromosome duplication could easily be reversed a generation later, but a chromosome loss would be almost impossible to reverse (except in cases where it was a duplicate of another chromosome).
I was under the impression that he was hinting of going back very far on the lineage. I'm wondering just how far "backwards" he was referring to. But I tend to agree with you that selective pressures + isolation + mutation does all sorts of weird things. I would think that whatever adaptations evolved could just as easily go back via deletion/insertion.
But Dr. Adequate is right in that a significant nucleotide change would kill an organism before it gave it a chance to populate further. Somewhere in the order of three base changes, maybe? I don't know. I think in practical terms it would be unremarkable, such as the Galapagos finches you spoke of.

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 Message 41 by Dr Adequate, posted 06-07-2009 8:08 AM Hyroglyphx has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 41 of 49 (511171)
06-07-2009 8:08 AM
Reply to: Message 40 by Hyroglyphx
06-07-2009 7:57 AM


Re: Answer is in the question
But Dr. Adequate is right in that a significant nucleotide change would kill an organism before it gave it a chance to populate further. Somewhere in the order of three base changes, maybe?
Not likely: given the mutation rate, you yourself have many more single nucleotide substitutions than that, in the order of about 100.
See A.S. Kondrashov, Direct estimates of human per nucleotide mutation rates at 20 loci causing Mendelian diseases.
Edited by Dr Adequate, : No reason given.

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Hyroglyphx
Inactive Member


Message 42 of 49 (511172)
06-07-2009 8:17 AM
Reply to: Message 41 by Dr Adequate
06-07-2009 8:08 AM


Re: Answer is in the question
Not likely: given the mutation rate, you yourself have many more single nucleotide substitutions than that, in the order of about 100.
I stand corrected.

"An idealist believes the short run doesn't count. A cynic believes the long run doesn't matter. A realist believes that what is done or left undone in the short run determines the long run." --Sydney J. Harris--

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Larni
Member (Idle past 163 days)
Posts: 4000
From: Liverpool
Joined: 09-16-2005


Message 43 of 49 (511183)
06-07-2009 1:04 PM
Reply to: Message 19 by doc
05-24-2009 11:57 AM


doc writes:
If it's very, very unlikely for evolution to go "backwards" then it's also....snip
Sabre tooth traits have evolved and been lost several time in mammalian evolution. From creodonts to nmravis to cats to Thylacosmilus.

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 Message 19 by doc, posted 05-24-2009 11:57 AM doc has not replied

Replies to this message:
 Message 45 by Wounded King, posted 06-10-2009 5:35 AM Larni has replied

  
Taq
Member
Posts: 9970
Joined: 03-06-2009
Member Rating: 5.6


Message 44 of 49 (511384)
06-09-2009 3:20 PM


I tend to see things from a genetic perspective. As Dr. Adequate points out, there are over 100 point mutations in each individual in each generation (not to mention the rare indel). There is no way that a species can reverse this accumulation of mutations and return to the genotype of their ancestors. So from a genetic point of view, evolution can not be reversed.
However, from a morphological point of view there can be a "reversal". That is, adaptations can go away and then re-evolve. Someone else mentioned the canines of cats, which is a really good example. To continue with that example, it's an arms race. In order to avoid predation the prey species gets larger. In order to kill the larger prey larger canines are selected for. The prey and predator co-evolve. Pretty soon, the cats are highly adapted to killing just one large prey species. If that prey species disappears so do they. This opens a niche for another prey species to evolve a larger morphology, and so it starts again.
However, at the genetic level each species of big cat will be different. While the same general morphology may re-evolve the genes do not.

  
Wounded King
Member
Posts: 4149
From: Cincinnati, Ohio, USA
Joined: 04-09-2003


Message 45 of 49 (511524)
06-10-2009 5:35 AM
Reply to: Message 43 by Larni
06-07-2009 1:04 PM


I'm not sure that 'loss' in this case is really what happened. Didn't many of these species/lineages simply go extinct? Are you suggesting that creodonts were ancestral to modern carnivora? This example is certainly very distinct from the walking stick case.
Your examples seem to better counter what Doc wrote after the section you quoted ...
.. then it's also very, very unlikely for it to follow the same steps and end up with the "same" solution.
A claim which your examples or even a tenuous familiarity with the concept of convergent evolution would show to be incorrect.
TTFN,
WK

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