The Loom

Surprises in Jelly

Jellyfish.jpg
I’ve got an article in today’s New York Times about jellyfish and their kin—known as cnidarians. Cnidarians look pretty simple, which helped earn them a reputation as simple and primitive compared to vertebrates like us, as well as insects, squid, and other creatures with heads and tails, eyes, and so on (known as bilaterians). But it turns out that a lot of the genes that map our complex anatomy are lurking in cnidarians, too. Scientists are now pondering what all that genetic complexity does for the cnidarians. They’re also using these findings to get a better idea of how the major groups of animals evolved between 600 and 500 million years ago.

For those interested some of the gorey details, check out PZ Myers’s take. Be sure to follow the links to earlier comments on some of the key papers on this research, plus diagrams.

In addition, curious readers can check out:

The timing of the evolution of cnidarians and bilaterians (full text)

An ode to the starlet sea anemone, which has revealed a lot of the secrets of the cnidarians (abstract only)

The evolution of diploblasty (development from two embryonic layers)

Update, 4:20 pm: PZ Myers link fixed (and spelling corrected!).

Comments

  1. #1 Charlie Wagner
    June 21, 2005

    Carl Zimmer wrote:
    “Much to their surprise, the scientists found that some genes switched on in embryos were nearly identical to the genes that determined the head-to-tail axis of bilaterians, including humans. More surprisingly, the genes switched on in the same head-to-tail pattern as in bilaterians.

    Further studies showed that cnidarians used other genes from the bilaterian tool kit. The same genes that patterned the front and back of the bilaterian embryo, for example, were produced on opposite sides of the anemone embryo.

    The findings have these scientists wondering why cnidarians use such a complex set of body-building genes when their bodies end up looking so simple.”

    Indeed…

    What it’s got me to wondering is how genes can “evolve” before the organisms that use them. It seems to me that these genes were there from the very beginning, they didn’t “evolve” from other genes, they were part of a program of evolution in which more complex structures emerged by switching on genetic potential that was already present.
    It is evidence that what you call evolution is in reality the unfolding of a program that was already present in the genomes of primitive organisms at the time of their initial arrival on earth.
    How is the information about Cnidarian genetics you describe consistent with the darwinian mechanism of random mutation and selection? It seems to me that the presence of genetic potential in organisms before this potential is realized falsifies the darwinian view of evolution and supports the notion that the genes did not evolve along with the structures and processes they control, but were there before these processes and structures emerged.

  2. #2 Carl Zimmer
    June 21, 2005

    During evolution, genes are duplicated and undergo mutations. These new, evolving genes take on new functions. Entire networks of these genes can then be co-opted for new uses.

    The genes I discuss in my article were not present in the common ancestor of all life on Earth. They do not exist in bacteria, for example. They do not even exist (as far as scientists know) in sponges. Only after the ancestors of cnidarians and bilaterians diverged from sponges did they emerge.

  3. #3 scott ecksel
    June 21, 2005

    “Surprise” is an understatement. Would this also affect the taxonomic placement of Ctenophores?

  4. #4 Charlie Wagner
    June 21, 2005

    Carl Zimmer wrote:
    “The genes I discuss in my article…”

    Thanks for the reply.
    Unfortunately, it is less than satisfying.

    http:www.charliewagner.com

  5. #5 taylor
    June 21, 2005

    “It is evidence that what you call evolution is in reality the unfolding of a program that was already present in the genomes of primitive organisms at the time of their initial arrival on earth.”

    Jeez, that’s clueless. Didn’t know there were Raelians lurking here.

  6. #6 Traffic Demon
    June 21, 2005

    To steal a phrase, “Nobody cares what you think Charlie.”

  7. #7 Linkmeister
    June 21, 2005

    There’s something wrong with the link to Pharyngula.

  8. #8 G Lynn
    June 21, 2005

    Trafic Demon

    “Nobody cares what you think Charlie.”

    Don’t you get it yet – he does not think – that is the whole point.

  9. #9 Blue Collar Scientist
    June 22, 2005

    …darwinian mechanism of random mutation and selection?

    Random mutation and selection? Give me a break.

    The theory of natural selection says, clearly and above all else, that selection is NOT random. According to this theory, those individuals in a population that are poorly adapted to their environment are most likely to die without having reproduced. This is quite different from having individuals killed off according to a dice roll.

    Nor is mutation fully random, in the strictest sense. Certain kinds of mutation (such as doublings of series of genes) are far more likely than other kinds of mutations (such as ones that suddenly introduce a brand new set of fully expressed developmental genes). So while specific outcomes are fairly random, the likelihood of overcopying of already effective genes is much stronger than the creation of genes ex nihilo in a mutation event. And as expected, most mutated individuals are either unaffected by the mutaton, or hurt by it. The latter individuals are nonrandomly removed from the population due to their unfitness.

    The fact is, “random mutation and selection” is a lie about what evolution is, perpetrated by fringe antiscience activists because without telling this lie, they have an immeasurably more difficult time convincing others that their further lies about evolution are true.

    Somebody should have pointed out the fact of nonrandom selection fairly immediately. I’m surprised Carl let it slide.

  10. #10 Charlie Wagner
    June 22, 2005

    Blue wrote:

    “Somebody should have pointed out the fact of nonrandom selection fairly immediately.”

    The question of whether or not selection is random is a red herring.
    Clearly, it is not random, those individuals better equipped to survive will have a selective advantage.
    But this is irrelevant. Selection can only work on variation that is already present. It has no power to organize, integrate or create new processes, structures, systems or organisms. This variation is the product of mutation, and mutations are mostly random.
    Therefore, it is correct to say that the process of evolution itself, as descibed by Darwin and his successors, is a random process.

  11. #11 DeafScribe
    June 22, 2005

    The real news here is simply that even the most ancient genes are conserved and re-used. This is consistent with an evolutionary perspective; genes adapted for a given purpose are re-purposed and employed for a variety of functions. That suggests highly plastic, mallable, dynamic responses to environmental and evolutionary pressures.

    By itself, this doesn’t refute the ID view; but it certainly adds to the enormous body of evidence that does.

  12. #12 Charlie Wagner
    June 22, 2005

    Deaf wrote:

    “The real news here is simply that even the most ancient genes are conserved and re-used.”

    Yes indeed. In fact, the same genes are used over and over in a wide variety of forms and applications across a broad range of structures and processes.
    This is of great significance. But it begs the question: “where did these genes and the regulatory mchanisms that control their deployment come from”?
    I fail to see how this contributes in any way to refuting the notion of intelligent input. In fact, it supports the notion that evolution, like development, is the unfolding of a program that is already present in the genome and has been from the very beginning, rather than a haphazard accumulation of fortuitous accidents occurring over time.

  13. #13 doug
    June 23, 2005

    Isn’t it amazing how everything seems to provide evidence for evolution? The brain shrinks in some form of pygmy homo erectus. Thats evolution! Ancient genes survive millions of years unchanged. That’s evolution?! Women have orgasms. That’s evolution! Although not all women have orgasms and they still manage to reproduce hmm luckily with the right spin…That’s evolution! We live in a civil society with people working for cooperative goals. That’s evolution! Unfortunately some people murder and rape. Just an unfortunate side-effect, but that’s evolution.

    Not only is everything evidence for evolution but evolution explains everything! No its not circular reasoning its Evolution!
    Thank goodness we don’t need to resort to God to explain the world around. Now we have Evolution! Its the all-encompassing answer to the ultimate question (I always thought it was 42). The evolutionist has reached the omniscient nirvana. maybe we should start meeting at the biology lab on Sunday mornings. We can sing some Evolution Hymns. Do they exist? Don’t worry they’ll evolve. I’ll just start selectively pressing some keys on the organ and type a few letters while blindfolded. Okay I’m getting a little carried away…chalk it up to evolution.

  14. #14 andrew burnes
    July 1, 2005

    holy crap. i just want to learn about evolution, and everywhere i go there’s some jackass creationist throwing stinkbombs. i really do think that blogs are great conversational forums (fora?) in which to broaden your understanding of complex subjects but is there anywhere on the web that you can learn something without being harrassed by morons?

  15. #15 Steve Russell
    July 1, 2005

    We have every good reason not to waste any further time or effort on Doug. (And presumably everybody already knows that CW should be ignored.) Doug posted exactly these same “arguments”–which now turn out to be merely regurgitated from ID lawyer Phillip Johnson–on an earlier thread, Carl graciously responded, and many other commentators attempted to sddress Doug’s “concerns.”

    Doug simply ignored many of the points made, twisted and squirmed to avoid the fair impact of others, and is now reduced to simple repitition. In short, he’s now been revealed as yet another close-minded troll.

    Bye, Doug.

  16. #16 Bagaaz
    July 2, 2005

    Doug babbled : “Not only is everything evidence for evolution but evolution explains everything!”

    Funny that. If there is something that evolution can’t currently explain it’s usually exploited by creationists.

    We used to have:

    “Evolution can’t explain X, therefore evolution is wrong”.

    Now we have:

    “Evolution explains everything, therefore evolution is wrong”.

    There’s just no pleasing those dumb creationists.

    (Yes, I know that he basically cut and pasted that rubbish, we all know that intelligent information cannot be created by creationists as that would falsify ID-ism)

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