New body plans — a thought experiment

Since there’s been some discussion on new body plans, here is my understanding of how they come about. Note that I am not a biologist. I’m sure someone will correct me if I am wrong. Most of this has to do with how branching processes work.

To explore how new body plans arise, we are going to travel back in time with my trusty time machine. I obviously don’t have a time machine, which is why this is only a thought experiment. As I travel back in time, I take along a passenger, whom I shall call “William”. We want to find out where the octopuses, with an obviously different body plan, arose.

We start our journey in the present, looking at a person — perhaps at William himself. Then we go back in time to look at the ancestors. Well go fast, or this would take for ever.

As we go back in time examining ancestors, we see earlier vertebrates, such as fish. We keep on going, and get to the early chordates. They had a neural bundle, but no vertebrae. We have to go further back to find the ancestors of the octopus. As we go back, we see ancestors without even a neural bundle. Eventually, we get back to the point where the ancestors of the octopus branched off.

At this point, we see two sibling organisms. One of those is an early ancestor of us, and the other is an early ancestor of the modern octopus.

I hand William a microscope, and ask him to examine both as closely as possible, and to describe the body plan that he can see in each. “What body plan” says William. “I don’t see any body plan.”

That’s where the phylum branching occurred. The body plans came later. The whole idea of “macro-evolution”, as that term is used by creationists and ID proponents, is just a complete misunderstanding.

65 Replies to “New body plans — a thought experiment”

  1. petrushka
    Ignored
    says:

    But the HOX gene that enables body plans preceeds multicellularity.

  2. Mung Mung
    Ignored
    says:

    petrushka:

    But the HOX gene that enables body plans preceeds multicellularity.

    A single hox gene that enables body plans. Do tell.

  3. petrushka
    Ignored
    says:

    Surveys of Hox genes in various arthropods and related phyla demonstrate that extensive duplication and diversification of Hox genes occurred long before the appearance of overt sdoctopicegmental diversity in arthropod body plans.

    http://www.cell.com/current-biology/abstract/S0960-9822(06)00321-6

    Posting from a tablet, so linking references is difficult. If you actually interested, you can find them. The point is that the genes preceded body plan diversification and even preceded multicellularity.

    The different hox genes are largely the result of duplication.

  4. Mung Mung
    Ignored
    says:

    petrushka,
    Your original claim was as follows:

    But the HOX gene that enables body plans preceeds multicellularity.

    Do you have any evidence whatsoever to support this assertion? Did I somehow manage to “quote-mine” your original assertion?

    Here’s what you asserted:

    A single HOX gene “enables” body plans. The single HOX gene that “enables” body plans preceeds multicellularity.

    Neither claim is supported by your link.

  5. petrushka
    Ignored
    says:

    I didn’t use the word “single,” but that is irrelevant look up hox gene in wikipedia and follow the references. There are more than a dozen variations, but they have a common ancestor that originated before body plans.

    Body plans are the result of regulation rather than the result of new genes. In general the hox genes themselves haven’t changed much since the cambrian.

    Most of the difficult evolution — the invention of proteins — occurred in bacteria prior to the cambrian. Regulation of development was the breakthrough that enabled multicellularity and body plans.

  6. DNA_Jock
    Ignored
    says:

    MAT alpha2

  7. petrushka
    Ignored
    says:

    My interest in all this is to find out if there is anything new coming out or the ID camp. As best I can determine, the Darwin’s Doubt argument is that biologists haven’t really looked at the Cambrian or wondered what happened.

    That would be silly.

    If you want a readable account of molecular evolution and what the Cambrian is about, try Koonin’s Logic of Chance. I got it and read it because it was recommended by UD. Imagine that.

  8. Blas
    Ignored
    says:

    petrushka:

    Most of the difficult evolution — the invention of proteins — occurred in bacteria prior to the cambrian. Regulation of development was the breakthrough that enabled multicellularity and body plans.

    If this is true, you do not need CD anymore. If all the proteins were already present in bacteria, and only needed rearrangement of regulatory expression of them, you do not need cumulative ramdom mutations to go from one from the other. Re-arrangements of genes are indepenedant of the starting point.
    That it is not darwinism.

  9. petrushka
    Ignored
    says:

    Read Koonin. You aren’t even making sense.

    Bacteria exchange genetic material. Always have. Lots of horizontal transfer.

    Common descent is more obviously applicable to multi-cellular organisms. At least in figuring out vertical lineages.

  10. Blas
    Ignored
    says:

    petrushka:

    Common descent is more obviously applicable to multi-cellular organisms.

    I was talking about multice-cellular organisms.

    petrushka:

    At least in figuring out vertical lineages.

    You do not need figuring out vertical leneages, hox genes rearrangements do not need siilar ancestors.

  11. petrushka
    Ignored
    says:

    Blas, if you want to be a critic of biology, you shouls at least make an effort to understand how terms are used. “Darwinism” isn’t used at all in peer reviewed papers, so right away you mark yourself as a crank.

    If you want to comment on common descent, get a book by Koonin or Ernst Mayr and give aus a reference to something they say thatt is incorrect.

  12. petrushka
    Ignored
    says:

    Blas, if you are denying common descent in multi-celled organisms, you are out of step with just about everyone, including Koonin, Shapiro, Behe. It really isn’t worth the time discussing this.

    If there were any way to deny common descent, Behe would be all over it.

  13. Mung Mung
    Ignored
    says:

    petrushka: I didn’t use the word “single”

    so?

    what you did say was:

    “the HOX gene that enables body plans preceeds multicellularity.”

    A misquote?

    Which HOX gene did you have in mind?

  14. DNA_Jock
    Ignored
    says:

    As I said
    MAT alpha2
    Its interaction with MATa1 is interesting.

  15. petrushka
    Ignored
    says:

    I had in mind the first. The common ancestor of the extant HOX genes. It and most of its variants were invented before multicellularity.

    An interesting example of a gene evolved for one benefit and acquiring new functions.

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