An Animal Toolkit in a Single-Celled Organism
by MikeGene
Choanoflagellates are single-celled organisms that are mentioned in The Design Matrix
Recently, the choanoflagellate genome has been sequenced. These protists have abouit 9200 genes, far less than the 25,000 seen in flies or humans. Yet the genome shows an abundance of data that further strengthen the plausibility of front-loading.
I have not had the chance to look over the research article yet, but consider some excerpts from the ScienceDaily review:
One finding confirmed by the sequencing is that choanoflagellates have many genes that, in animals, produce proteins essential to cell-to-cell signaling and in determining which cells stick to one another. Since Monosiga does not form colonies as do some other choanoflagellates, these proteins' roles are a mystery, King said.
"In animals, some of these proteins, called cadherins, evolved for linking cells together; they are the glue that prevents clumps of cells from falling apart," King said. "Choanoflagellates show no hint of multicellularity, but they have 23 genes for cadherin proteins, about the same as the fruit fly or the mouse."
In other words, these single-celled organisms are loaded with genes that had previously thought to be unique to multicellular organisms because they function in an extracellular context. But it gets better:
The choanoflagellate genome, like the genomes of many seemingly simple organisms sequenced in recent years, shows a surprising degree of complexity, King said. Many genes involved in the central nervous system of higher organisms, for example, have been found in simple organisms that lack a centralized nervous system.
Likewise, choanoflagellates have five immunoglobulin domains, though they have no immune system; collagen, integrin and cadherin domains, though they have no skeleton or matrix binding cells together; and proteins called tyrosine kinases that are a key part of signaling between cells, even though Monosiga is not known to communicate, or at least does not form colonies.
It is now clear that many genes, once thought to exist only to service the needs of multicellular life can exist in a unicellular context for hundreds of millions of years. The hypothesis of front-loading evolution continues to become more attractive.
——
* Some background.
* And for my own notes, an unrelated echo of front-loading (?): The authors write: "The surprising similarities in the patterns of neural stem and intermediate progenitor cell division in Drosophila and mammals, suggest that amplification of brain neurogenesis in both groups of animals may rely on evolutionarily conserved cellular and molecular mechanisms."
February 23rd, 2008 at 6:23 pm
Hi Mike,
Please don't take this as a negative comment but…
How do the scientists know these "single-celled organisms" didn't evolve from a much older and long extinct multi-celled organism?
If I am reading the article correctly, I also understand there might be a predatory reason for the cadherins (capture other cells for food).
However, even with the Duck view of things, this is interesting and comes across as having quite a bit of fortuitous foresight. And it is interesting that the gene has been preserved for as long as it has for not having any obvious benefit for this organism.
All in all, it looks like good Science Stuff
Comment by Thought Provoker — February 23, 2008 @ 6:23 pm
February 23rd, 2008 at 6:24 pm
So glad you picked up on that, Mike! It had "you" written all over it… §;o)
Comment by Joy — February 23, 2008 @ 6:24 pm
February 23rd, 2008 at 7:51 pm
Mike:
Very interesting stuff. But despite all the fancy front-loading, choanoflagellates are still single-celled. What was The Front-loader smoking that day?
An interesting question is what the functions of those genes are in choanoflagellates. And how did they become co-opted in other organisms to do what they do today?
Comment by Raevmo — February 23, 2008 @ 7:51 pm
February 23rd, 2008 at 7:57 pm
Raevmo:
What is the point of this comment? Still single celled? That just strengthens front loading even more.
Comment by Bradford — February 23, 2008 @ 7:57 pm
February 23rd, 2008 at 8:22 pm
Bradford:
Apologies for being unclear about my point. If all those front-loaded genes were meant to achieve the evolution of multi-cellular organisms, why didn't it work out that way in the choanoflagellates, who are still uni-cellular? Is that just some stochasticity?
Comment by Raevmo — February 23, 2008 @ 8:22 pm
February 23rd, 2008 at 8:29 pm
Raevmo:
If the intent is the outcome we observe today then one should expect that some unicellular organisms evolved and their descendents became very much unlike them. However, why would unicellular organisms have to disappear in the process?
Comment by Bradford — February 23, 2008 @ 8:29 pm
February 23rd, 2008 at 8:52 pm
Bradford:
Sigh. You can never test any theory that claims the intent is the outcome we observe today. Every observation today automatically vindicates the theory.
I want to know why those choanoflagellates got front-loaded with all those fancy genes but didn't evolve the properties those front-loaded genes were meant to accomplish in the end. Or is it too early to tell?
Comment by Raevmo — February 23, 2008 @ 8:52 pm
February 23rd, 2008 at 8:55 pm
Bradford:
Raevmo's just falling back on the good ol' "if humans are descended from monkeys, why are there still monkeys?" gambit. That of course he'd reject as idiotic if you were to make that "Creationist" argument… §;o)
Comment by Joy — February 23, 2008 @ 8:55 pm
February 23rd, 2008 at 9:09 pm
Raevmo
I like Denton's principle of plenitude as the intent of the designer. It does a good job of accounting for why there are still singled celled organisms with out saying that what we see must of been what he intended.
Peace
Comment by fifth monarchy man — February 23, 2008 @ 9:09 pm
February 23rd, 2008 at 11:34 pm
Hi TP,
This is possible and it would be just as interesting if this was the case (although, for different reasons). I seem to recall reading a paper by King where she considers this possibility and did a good job of knocking it down (although the intron stuff mentioned in the ScienceDaily argument might resurrect this objection). I'll keep an eye out for it, as it's buried in my stack.
Sure. As I argue in The Design Matrix, mutli-cellular genes are going to need some function in a uni-cellular state to persist. What matters is that the cadherins are not essential for protist life. But 23 copies? One has to wonder if such extensive duplication (and divergence?) is needed for simple prey capture. Perhaps their function is more sophisticated.
Comment by MikeGene — February 23, 2008 @ 11:34 pm
February 23rd, 2008 at 11:35 pm
Hi Raevmo,
I never claimed that "choanoflagellates got front-loaded with all those fancy genes." Choanoflagellates share a common ancestor with animals, as this single-celled ancestor likely had these shared genes (and more). Since then, the choanoflagellate lineage may have lost some essential genes needed to move toward metazoan evolution.
What choanoflagellates clearly demonstrate is that genes, long thought to be metazoan-specific because of their function in metazoans, can indeed exist in a unicellular state across deep time. The case for front-loading evolution becomes increasingly plausible.
Comment by MikeGene — February 23, 2008 @ 11:35 pm
February 23rd, 2008 at 11:37 pm
Let mequote Krauze:
Comment by MikeGene — February 23, 2008 @ 11:37 pm
February 23rd, 2008 at 11:58 pm
It's probably worth noting at some point that there is a pretty strong alternative explanation: that these genes existed first for other reasons (which may or may not still be in use in Cfs around today) and were then co-opted for use in multicellularity.
In this sense, a lot of the language here about things being "in place" is a bit misleading. What we have are similar things that both multi-cellular and single-celled creatures around today share. But they aren't identical in modern animals, don't generally do the same sorts of things, and the idea that they are inherently multi-cellular was based on seeing them as playing a crucial role in multi-cellular organisms. Now we know better: they are more adaptable than we had thought. That's a more comprehensive summary anyway.
And Mike, did you see my question in the culture war thread?
Comment by Bad — February 23, 2008 @ 11:58 pm
February 24th, 2008 at 1:23 am
Another case of how the "Darwinian" view of life has actually hindered Science? Certainly this is not a prediction of Darwinism?
Co-option does not resolve the problem. Why would evolution have a tendency to produce genes which were "co-optable"
On a Darwinian view, co-optation is pure chance. On a DM view, co-option is to be expected.
Where does the evidence lead?
Comment by Mung — February 24, 2008 @ 1:23 am
February 24th, 2008 at 6:42 am
Mung:
A case where modified versions of genes present in single-celled organisms play a role in adaptive traits of multi-cellular organisms. Nope. No way "Darwinists" could have thought of that.
If it weren't for them Darwinists, high-speed DNA sequencing would have been invented at least a 100 years ago.
Comment by Raevmo — February 24, 2008 @ 6:42 am
February 24th, 2008 at 11:51 am
Hi Raevmo,
You wrote…
I tend the think sarcasm rarely provides effective communication, especially in blogs.
I try very hard not to do it myself (and believe me, I am often tempted).
While you probably could have got the point across without resorting to sarcasm, I think you made a good point.
In the Linux thread we are talking about the importance of evidence and explanation when trying to gain understanding.
If I read your sarcastic point correctly, whether or not methodological materialism is an appropriate label it means that scientists are very focused on finding tangible physical evidence. Be it with better, faster DNA sequencing or bigger, faster super-colliders.
I lean towards looking for explanations. The logical chain of how things work. While evidence is important, I think understanding is more important, IMO.
I suggest that there is some merit in the criticism that a movement which doesn't seem overly interested in finding new evidence or offering detailed hypotheses is probably more focused on belief than on science.
So the non-sarcastic response to Mung is that the only thing possibly "hindered" was an inference of a preferred belief.
A belief in something that happens to be true isn't knowledge.
Comment by Thought Provoker — February 24, 2008 @ 11:51 am
February 24th, 2008 at 12:27 pm
Hi Mike,
I hope you are not too angry at me for my role in the usual off-topic distractions.
I was going to try to get back to focusing on the details of the Choanoflagellates but decided to explore a more general question that has me curious.
In the opening post you wrote…
As much as I think your approach to ID is a vast improvement over the standard approaches, you are still doing quite a bit of handwaving when it comes to your explaination (i.e. "hypothesis of front-loading evolution").
Is this the reason you are holding back on calling it science?
Comment by Thought Provoker — February 24, 2008 @ 12:27 pm
February 24th, 2008 at 1:25 pm
And what is supposed to be the "handwaving?"
Comment by MikeGene — February 24, 2008 @ 1:25 pm
February 24th, 2008 at 1:46 pm
Yes. Was it important?
Comment by MikeGene — February 24, 2008 @ 1:46 pm
February 24th, 2008 at 2:08 pm
Hi Mike,
My comment wasn't supposed to be a criticism.
I had been reluctant in the past to bring it up because I was afraid of a negative reaction.
Yes, I think your Front-loading hypothesis is vague enough to allow unsupported presumptions.
But then again in a lot of ways so is my Third Choice.
You are already aware of my confusion/disagreement with your tendency to presume the existence of a human-like intelligence doing the front-loading.
You do a good job of trying to build a case on foreshadowing with things like Choanoflagellates and hen's teeth. But I don't know how that fits in your "hypothesis of front-loading evolution".
I am an engineer, I like to build thought models and use them to see how the puzzle pieces fit (modifying the models as needed).
I understand how Choanoflagellates might fit in with my model of a quantum spacetime wavefunction of a universe being consistent with itself.
I am having difficulty doing the same thing with your model, because I don't understand your model unless it involves a very powerful being with human-like intelligence.
Please pardon the honesty and please believe me when I say I am earnestly trying to see things from your viewpoint.
That is why I asked if you were intentionally forgoing suggesting a scientific hypothesis until you have gathered more evidence.
That is a perfectly understandable position and is consistent with what I understand is your justification for saying "ID is not science".
Comment by Thought Provoker — February 24, 2008 @ 2:08 pm
February 24th, 2008 at 2:16 pm
TP:
I'm certainly not one to rule out a powerful intelligent being but why is it not evident to you that a quantum based model could be consistent with a front loading concept? The quantum model would be the start of a process that transitions to a biological one at some point. The evidence is another matter but where are the conceptual difficulties?
Comment by Bradford — February 24, 2008 @ 2:16 pm
February 24th, 2008 at 3:35 pm
Hi Bradford,
Maybe you missed the part where I consider The Third Choice to be an ID hypothesis based on many of the same arguments Mike uses for Front Loading.
I also think The Third Choice is a Front Loading hypothesis, but I can't make that call officially.
I even came up with a variant called The Third Choice, ID Version that removes any vestiges of doubt as to it being an ID alternative. However, I feel the ID Version violates the NOMA separation of science and philosophy.
P.S. for those that don't like to click links…
Comment by Thought Provoker — February 24, 2008 @ 3:35 pm
February 24th, 2008 at 4:04 pm
What types of genes are not co-optable? Can a non-co-optable gene even be produced?
Comment by One Brow — February 24, 2008 @ 4:04 pm
February 24th, 2008 at 8:48 pm
Hi TP,
I'm not sure why you are confused, as I have clearly explained this before. So again, I presume the existence of a human-like intelligence because I have massive experience with human intelligence and I seek to apply this experience to a subject I know a few things about (biology). There is nothing complex or conspiratorial about it "“ it's just a convergence of ability and curiosity. Whether the endeavor will pay-off in the end, I cannot say and I will probably never know. What I can say is that if I don't do it, who else will? Is there someone out there who could have written The Matrix? Who? If I don't finish vol 2, is there someone else who will? Who?
Such examples help to illustrate the plausibility of front-loading and also help me think about possible mechanisms of front-loading. The choanoflagellate example also puts to rest a common criticism that was raised when I first began to propose front-loading.
And I'm a loud mouth on the internet who used to build plastic car models.
Why would the intelligent agent have to be "very powerful?"
I'm not arrogant or presumptuous enough to declare my internet/book speculations are Science. In fact, I think it is silly to try to force all of human inquiry into tidy, yet vaguely defined, little boxes.
Comment by MikeGene — February 24, 2008 @ 8:48 pm
February 24th, 2008 at 9:46 pm
TP, how can you not see the fit?
Comment by Bradford — February 24, 2008 @ 9:46 pm
February 25th, 2008 at 7:04 pm
Raevmo Says: A case where modified versions of genes present in single-celled organisms play a role in adaptive traits of multi-cellular organisms. Nope. No way "Darwinists" could have thought of that.
If it weren't for them Darwinists, high-speed DNA sequencing would have been invented at least a 100 years ago.
Darwin didn't think of it either.
You, Raevmo, are not a "Darwinist" anyway, so what of it?
Who GAS about Darwin?
This is the 21st Century! Is it possible for biological theory to climb out of the 19th Century?
And "Darwinists" didn't "invent" (re-invent) high-speed DNA sequencing.
Intelligent designers did. (You know, like Linux. LOL)
Comment by Rock — February 25, 2008 @ 7:04 pm
February 25th, 2008 at 7:55 pm
Mostly agreed, Rock.
Darwin was a helluva scientist, even if his ideas have evolved enormously. Projection on the part of True Believers (like Mung apparently) makes them think he is a god-like figure for contemporary evolutionary scientists. They need the Big Authority in their lives, so they think everybody needs that. Not.
Feels good to do some stereotyping, though. Yes, TP, I know sarcasm doesn't optimize efficiency of communication, but I am still a "young buck" (well, so I like to believe) without the wisdom and self-control that cometh with a certain age. Or not.
Comment by Raevmo — February 25, 2008 @ 7:55 pm
February 26th, 2008 at 6:36 pm
Christmas, Presidents' Day, Martin Luther King day, Darwin Day…oops!
Sure, sure, he's not a Big Authority.
Can I interest you in some Darwin Day cake?
http://farm1.static.flickr.com...
Or a Darwin Day party?
http://images.google.com/imgre...
Comment by kornbelt888 — February 26, 2008 @ 6:36 pm
February 26th, 2008 at 6:41 pm
kornbelt888:
Raevmo is a proud member of a European socialist paradise by his own acknowledgement. Big Authority doesn't come any bigger than Big Gubbermint.
Comment by Bradford — February 26, 2008 @ 6:41 pm
February 26th, 2008 at 7:31 pm
Celebrating someone's birthday and contributions to science is not quite the same thing as worshiping and pretending to have a personal relationship with them long after they're dead. Not in my book anyway. So when is the next coming of Darwin scheduled?
Bradford:
Are you sure you want to compare my Big Gubbermint with your Big Gubbermint (BG)?
My BG doesn't intern people without habeas corpus. My BG takes care of the weakest members of society. My BG offers universal health care. My BG offers cheap high quality university education. Ask yourself: what would Jesus do?
And despite our BG, we have far more paid vacation, we are happier, we have a higher per capita average income, and less inequality.
There's a lot of stuff that *ucks about my BG too, compared to your BG. But on balance, I believe my BG is far more humane than yours.
Not that I think you're buying any of this.
Comment by Raevmo — February 26, 2008 @ 7:31 pm
February 26th, 2008 at 7:42 pm
Yeh, Raevmo, if you weren't such a commie-pinko-fag-junkie-subversive-European… Why don't you cut your hair, shave your beard, Che, and wear a business suit and speak the English langauge?!
You aren't black, a woman, a child, disabled, or a Democrat are you?
Comment by Rock — February 26, 2008 @ 7:42 pm
February 26th, 2008 at 8:17 pm
Nah, just a perfect jump-off for stereotyping.
Comment by Bradford — February 26, 2008 @ 8:17 pm