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Another Explanation for Multicellular Life 87

Posted by Zonk
from the science-fight dept.
DrJay writes "Hot on the heels of Slashdot's coverage of a controversial model for a viral origin of the multi-cellular branch of life, Nature has published an alternative model that has nothing to do with viruses. Ars Technica's science journal has the rundown on the differences between these proposals." From the Ars article: "It's funny that this proposal for the origin of Eukaryotes should hit the popular press at a time where Nature has just published a hypothesis regarding the formation of the nucleus that has nothing to do with viruses, but everything to do with parasites. The parasites in this case are molecular: Type-II introns. These DNA sequences exist in both eukaryotes and bacteria, where they can insert in the middle of genes without causing harm because they can undergo chemical reactions by which they remove themselves from the RNA messages the genes make."
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Another Explanation for Multicellular Life

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  • Uh (Score:2, Funny)

    by Proc6 (518858)
    Well, there's someone that obviously doesn't know it's Friday afternoon.
    • Well, there's someone that obviously doesn't know it's Friday afternoon.

      What? This is slashdot. Do you really think we'd actually go out on a Friday night?
  • In a sense what's going on here is history, not science. We're not looking at generalisations, like physical laws, that can be repeated in a lab, but an event that happened once in our ancient history. It seems to me that it's a little futile to speculate on how cellular and multicellular life first appeared because the evidence was lost long ago.

    Towards the end of the 19th century the main French and British linguistic societies banned any further papers on the origins of langiage because unprovable spec

    • While we may never know, I do think this is a different situation. We can't really recreate the conditions under which language initially developed, but no doubt we will eventually be able to synthesize multicellular life.
      • We can't really recreate the conditions under which language initially developed, but no doubt we will eventually be able to synthesize multicellular life.

        But that would only tell us one way that life might form: in a test tube in some nanotech-era laboratory. That's probably not how it actually got started on Earth (although YMMV, especially if you're from Kansas.)

        However, I don't think it's a lost cause. The fossil record won't tell us anything here, but evidence may well come from the details of the

        • But that would only tell us one way that life might form: in a test tube in some nanotech-era laboratory

          Still, it could be something like an incredibly precisely-controlled Miller-Urey experiment, rather than an direct fabrication of life (though that could very well be harder to do).

          • Sure, but even Miller-Urey could only give us a plausible explanation for how life could have formed. Experiments such as these really can't tell us the explanation, can they?
            • No, they probably won't find the way.

              However, they can no doubt rule out a lot of ways that might help get closer to the truth of what actually happened.
            • Experiments such as these really can't tell us the explanation, can they?

              True, but what they can do is illustrate to those that think there is only one (magic, devine) just-add-water explanation that they're simply, demostrably incorrect.
              • True, but what they can do is illustrate to those that think there is only one (magic, devine) just-add-water explanation that they're simply, demostrably incorrect.

                Um, if someone believes that life needs an intelligent designer to start, and you intelligently design a device which creates conditions where life can start and then turn it on and watch lifeforms come to be, how have you disproven the belief ?-)

                • the use of intelligence would be in figuring out what naturally occuring circumstances could generate this event.

                  you wouldnt be intelligently designing multicellular life. you would putting some single celled organisms in a particular environment and waiting for spontaneous evolution to multicelled organisms.

                  if that environment was one that can be shown to have occured naturally in the dim and distant past, you have demonstrated a convincing mechanism whereby single cells could have evolved into multi

      • While we may never know, I do think this is a different situation. We can't really recreate the conditions under which language initially developed,

        Sure we can. We just need to bring up a bunch of people without ever talking to them, and watch them growl to each other. Of course it takes a pretty monstrous mindset to conduct this kind of experiment, but since the world seems headed towards another era of fascism, it is just a matter of time.

        no doubt we will eventually be able to synthesize multicellu

    • by Anonymous Coward

      It seems to me that it's a little futile to speculate on how cellular and multicellular life first appeared because the evidence was lost long ago.

      Wrong. The evidence is all around is in the branches of life existing today. The challenge to us is how to best interpret it the evidence of our biological past.

      It' wrong to say that science cannot make claims about past events. We can not only say definitely, for instance, that speciation occurs and that different species have common ancestors. Nowadays w

      • It' wrong to say that science cannot make claims about past events

        I never said any such thing. But I don't think we can make accurate claims about a specific event that happened a few billion years ago - even with the wealth of genetic evidence we have today. The genomes we see today are like a palimpsest - they're been edited again and again through evolution. There's no reason to believe that there is any readable sign of the first cellular or multicellular organisms. Of course we can accurately order

        • I don't think we can make accurate claims about a specific event that happened a few billion years ago - even with the wealth of genetic evidence we have today. ... I'm talking about an event in our deep past that will probably always be beyond reach.

          Well, maybe, maybe not.

          But one thing is certain: If you refuse to speculate, hypothesize, or test ideas, then it will certainly always be beyond your reach.

          And if it turns out not beyond our reach, someone other than you will solve the puzzle.

          The history of sc
      • Ah, Ah, Ah, science can from the available physical evidence imply theories about the "process", the "how it happened", but they are still largely in the dark about the "cause", the "why it happened". Why do these micro organisms behave this way?

        But if you look at insects that have been trapped in amber, that some say are 100 million years old. These don't look very much different from today's variety of the very same species. Is that not a strike against this "empirically observable rates of genetic dr
        • That would be awesome, if DNA lasted that long. They're just now finding proteins that have lasted 67 million years, but DNA itself is a whole different matter, not to mention a complete strand. It's very likely that it doesn't really exist past 30 million years, if that. Besides, a lot of the critters in question aren't actually body fossils (except those in amber, like you said) - they're imprints in sediment or carbon films left over from a decaying body. Incredible detail, sure, but no actual tissue
    • When was the last time a ban solved a problem?
    • We're not looking at generalisations, like physical laws, that can be repeated in a lab, but an event that happened once in our ancient history.

      How do you know it can't be repeated in a lab? In fact, there is increasing experimental evidence that the steps that lead to life are not a unique accident, but repeatable.

      (Not that repatability in a lab is a necessary or sufficient condition for something to be scientific anyway.)

      It seems to me that it's a little futile to speculate on how cellular and multicellu
    • It seems to me that it's a little futile to speculate on how cellular and multicellular life first appeared because the evidence was lost long ago.

      No, speculation -- coupled with observation and experiment -- is always useful. Even if we'll never know (without a time machine) how life did arise on Earth, knowing possible mechanisms helps both our understanding of biology as a whole as well as provides insights when looking for life elsewhere in the Universe.

      Indeed, it's possible that life arose several tim
    • Yes, I mean, who cares if people want to think? If it's controvertial, get rid of it! And next, we can start burning the books!
    • Science and history aren't exclusive. You can approach historical questions from a scientific perspective.
  • The Red Queen. (Score:5, Interesting)

    by TrevorB (57780) on Friday March 03, 2006 @06:04PM (#14846742) Homepage
    The vector is different, but the mechanism is the same. Multicellular life fighting an endless arms race against parasites.

    Anyone remotely interested in this discussion who has not yet read Matt Ridley's The Red Queen [amazon.com] should try to grab a copy from their library.

    More info on the Red Queen Hypothesis [wikipedia.org] at wikipedia.
  • Nahh... (Score:4, Funny)

    by inode_buddha (576844) on Friday March 03, 2006 @06:06PM (#14846756) Journal
    It was a mistake to come down from the trees, and the girls *still* wanted to be just friends. Prolly shoulda just stayed single-celled, it was a lot less hassle. Besides, no brain equals no pain.
  • How is an interon a "parasite" They provide useful genetic services by providing alternative splice points in eukaryotes. Calling them 'parasites' is nothing more then bread-dead flabbergastating (which I am defining, here and today, to mean acting flabbergasted at things which are not at all flabbergasting)
  • Does this article deal with the origins of eukaryotic cells? Or multicellular organisms? Because they are two different issues.
    • Re:huh? (Score:4, Informative)

      by AJWM (19027) on Friday March 03, 2006 @09:04PM (#14847758) Homepage
      Offhand I can't think of a multicellular organism that doesn't comprise eukaryotic cells.

      Sure, there are things that are colonies of prokaryotic cells, but those are recognized as organisms at the individual cell level, not the colony level. Do you have a counterexample?

      Of course, there are plenty of single-celled eukaryotic organisms, and I think that's what the article is really talking about.
  • they can insert in the middle of genes without causing harm because they can undergo chemical reactions by which they remove themselves from the RNA messages the genes make.

    Am I too much of a geek, or did this remind anyone else of a rather similar situation with source code, Ken Thompson's fascinating 'Reflections on Trusting Trust [acm.org]'?

  • I sure wish I had $199/year for a subscription to Nature, but I just don't. I guess I will be one of the "have nots". An intellectually inferior burger flippin' weasle, UNLESS... I'm missing something all of you know. How can I read this?
  • Subjects such as this make me wish I had chosen a rudimentary biology class in my first year of University so I could have a small idea of what exactly they are talking about in biological subjects.
  • by bllius69 (778318) on Friday March 03, 2006 @09:51PM (#14847937)
    For some basic (and free info), try NCBI's bookshelf: http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=B ooks [nih.gov] Molecular Biology of the Cell is nice, as is Biochemistry, or The Cell. (Note: Koonin works at NCBI).

    Or search Wikipedia, google, etc.

    1. "Most of the DNA in the cell is wrapped in a fat and protein membrane."

    Most of the DNA in "all" three kingdoms are wrapped up in proteins. In eukaryotes there is a membrane that surrounds the entire set of chromosomes (except during cell division) called the nuclear membrane. Chloroplasts and mitochondria are also surrounded by membranes. All membranes have proteins in them. In Prokaryotes, the entire cell is surrounded by at least one membrane, and the DNA is inside of this in the cytoplasm. It does not float freely. In prokaryotes, most chromosomes are circular (but not always) and most organisms have one chromosomes (but not always). In eukaryotes, most organisms have multiple linear chromosomes.

    NB: Membranes are comprised of lipids and proteins and in some cases other molecules like cholesterol. Lipids are also known as "fat" and there are many different types.

    2. Central dogma/transcription/translation.

    In prokaryotes, transcription (copying DNA to mRNA) and translation (translating the RNA to create polypeptide (protein) chains, done by the ribosome) are coupled. In eukaryotes it is uncoupled as the RNA has to be transported out of the nucleus through the nuclear pore, where the mRNA is then translated by ribosomes in the cytoplasm, or by ribosomes attached to the ER and exported.

    3. Prokaryote/Eukaryote introns

    Introns are not eukaryotic-specific. All three branches of life have introns, however, they are far rarer in the archaea and bacteria (especially rare). Some introns can self-splice (remove themselves), while others do not. Lots of different "types" of DNA can move themselves around, insertion sequences, transposons, phages, viruses, conjugative DNA, etc. This movement of DNA is a driving force in evolution itself, not merely in a host organism protecting itself from invasive DNA, but in the evolution of novel protein functions.

    4. Single/multicellular

    There are single-celled eukaryotes (yeast cells) and there are prokaryotes that form developmentally specialized conglomerations of cells (biofilms, cyanobacterial chains, mycelial hyphae) where some cells are specialized as compared to others. Many prokaryotes can signal to, as well as receive signals from, other cells.

    5. Mimivrius

    Mimivirus is interesting, but it is an extreme outlier. More work on the full range of virus forms and genome ranges will help in this arena. Some of the metagenomic projects will definitely help in this area. It's like attempting to hypothesize the evolution of mulicellular organisms based on the blue whale.

    6. Introns and domains.

    Proteins fold into 3D structures to perform functions. The basic unit is a domain, which are units that can fold into a 3D structure themselves and perform some function (basically). Exons and domains are not a 1 to 1 relationship. IMO, intron evolution has a lot more to do with alternative splicing events and regulation in developmental pathways than it does in driving new functions for genes (you can duplicate genes and domains without introns/exons).

    7. Membrane evolution.

    Membrane compartmentalization is a key step in evolution. Interestingly the prokaryotes (archaea and bacteria) have two different types of lipids, suggesting that in the early stages of this evolutionary step that two pathways were chosen, and both have been maintained since that time. Again, another point in evolution is not that one system is always better than another, but that endpoints are achieved through multiple pathways.

    8. Koonin et al., hypothesis.

    Their hypothesis is interesting. I haven't read the paper, but I have seen Koonin's seminar from a few months ago. Unfortunately there is so much we don't know yet. His ideas may be skewed towards analyses based simply on comparative genomics and not enough on biochemistry.

  • Hot on the heels of Slashdot's coverage of a controversial model [...]

    Slashdot covers news like David Spade's jacket covers Chris Farley's back. ;-)
  • Here is one suggestion:

    In some years experiments with timemachines will transport living cells back in time to before life was present here on earth.

    So, we create life.
    Thats intelligent design.
  • The effect upon existing organisms by viruses is cancer. It would be easier for Niagara Falls to flow backwards than a human body, (not to mention the concurrent ecology) to arise out of chemicals such as methane, ammonia, etc. These naturalist philosophers have never studied mathematics to any serious degree, or they would not propound such absurdities. The amount of taxpayer money wasted upon these grant-funded pinhead projects in order to free the rebellious so that they can lift up their heads and roll

We warn the reader in advance that the proof presented here depends on a clever but highly unmotivated trick. -- Howard Anton, "Elementary Linear Algebra"

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