1. Joined
    06 Mar '12
    Moves
    625
    03 Sep '13 17:493 edits
    I came across this piece:

    http://en.wikipedia.org/wiki/Muller%27s_ratchet

    “....Geneticists have long bet on the success of sexual reproduction over asexual reproduction based in a large part on the process known as Muller's ratchet, the mechanism by which a genome accrues deleterious and irreversible mutations after the host organism has lost its ability to carry out the important gene-shuffling job of recombination ...”

    But this seems to me total nonsense because, if it was true, bacteria and viruses would have become extinct long ago! In fact, I would guess most species would have become extinct in just the last hundred years or so! It seems obvious to me that, regardless of whether there is sexual or asexual reproduction, natural selection would continually weed out any deleterious mutations before any of them became widespread in a specie's genome. So I looked up this so-called “ Muller's ratchet” effect just to check my facts:

    http://en.wikipedia.org/wiki/Muller%27s_ratchet

    I was appalled to find highly flawed reasoning being used throughout the Muller's ratchet theory as explained in the above!
    For example, it says:

    “Asexual reproduction compels genomes to be inherited as indivisible blocks so that once the least mutated genomes in an asexual population begin to carry at least one deleterious mutation, no genomes with fewer such mutations can be expected to be found in future generations”

    -which is obviously false because 1, why should the individual with the least mutated genome have to have at least one deleterious mutation? ( -answer, no reason! ) and, 2, why should, suddenly and miraculously, ALL individuals of a population have one deleterious mutation before natural selection has a chance to weed it out? Obviously, any deleterious mutation generally starts off with just ONE (or at least only a few) individual having it and, in the many generations that follow, there would be ample opportunity for natural selection to weed it out WELL before it has a chance to spread to the whole population! Plus, even if such a mutation miraculously DID spread to the whole population and to every individual, what is stopping any individuals then being born with that mutation mutated back to its none deleterious version and then natural selection selecting for those individuals that don't have that deleterious mutation until, once again, the population is free of such a deleterious mutation? -this theory just makes no sense at all!
  2. Joined
    25 Nov '04
    Moves
    35786
    04 Sep '13 06:14
    Muller's theory was invented for a reason.

    Sexual reproduction has a cost. It is a higher cost than asexual reproduction.

    So the question was: Why has sexual reproduction proved so successful?

    Muller's theory, proposed more than 50 years ago, attempted to describe a hidden cost to asexual reproduction that would allow sexual reproduction to come out either even with or better than asexual reproduction.

    This theory was proposed before anything was known about how bacteria et. al were able to take up genetic material from the environment.

    The wiki page does mention Back Mutation.

    Evolutionary theory, backed by real world experiments is a fast moving field. I have not been up to date for the last 15 years, at least 🙂

    z
  3. Joined
    06 Mar '12
    Moves
    625
    04 Sep '13 08:145 edits
    Originally posted by zesty
    Muller's theory was invented for a reason.

    Sexual reproduction has a cost. It is a higher cost than asexual reproduction.

    So the question was: Why has sexual reproduction proved so successful?

    Muller's theory, proposed more than 50 years ago, attempted to describe a hidden cost to asexual reproduction that would allow sexual reproduction to come out e ...[text shortened]... nts is a fast moving field. I have not been up to date for the last 15 years, at least 🙂

    z
    Oh yes, I guessed that Muller's theory was invented for explaining why sexual reproduction has proved more successful over asexual reproduction despite its cost.
    But, surely we should all know better now because we should know this theory to be clearly false! We now know that the correct explanation is, instead, that sexual reproduction gives better and faster ability to genetic adapt to a changing environment and this ability often more than compensates for the high cost of sexual reproduction.

    This is why I cannot understand why it was even mentioned in the first link I gave! Didn't those evolutionary biologists that did that recent research keep up to date on these basic facts? Or did they simply fail to understand how natural selection actually works and thus how natural selection would inevitably stop any 'Muller's ratchet effect'!? -I can only wonder.

    In fact, I am surprised that the wiki page on this failed to mention that the Muller's theory it widely regarded as wrong and then explain why!

    The wiki page does mention Back Mutation.

    Yes, I noticed that. I also noticed how it strangely just left it at that and just immediately moved on instead of taking that to the natural next step by stating the obvious fact that the existence of back mutations is one of the reasons why the theory may be wrong! In fact, it gave no explanation of why the theory is or at least could be wrong nor even mentioned any common criticism of it. I was not too impressed by that!