One of the serious shortcomings of Intelligent Design is that it does nothing to provide any new or productive insights into the workings of biology. ID proponents seem to be at least vaguely aware of this failure, in that they do frequently claim to be thinking about working on a preliminary, tentative approach towards the beginnings of a potential research program (my paraphrase), but most of the effort has been directed towards political and legal enforcement of their ideas, rather than actually testing those ideas. One advantage of pursuing only legalisms is that they don’t give scientists anything to grapple. Invariably, when ID proponents do dip their toes in the scientific waters, they end up getting eaten by the sharks that lurk there.
One example: Paul Nelson, of the Discovery Institute, has been peddling a peculiar idea he calls “ontogenetic depth” as a scientific concept that emerges from Intelligent Design. To his credit, he has been presenting this idea in legitimate science venues, at the Geological Society of America and Society for Developmental Biology meetings. Note that getting on the program at these meetings is not subject to peer-review, so it is not automatically a recognition of merit that this work has been presented publicly. It is a good sign that Nelson is willing to expose his work to criticism, though.
I’m going to give it some criticism here. “Ontogenetic depth” is a developmental idea, and I’m a developmental biologist. Today I also get to play shark.
What is “Ontogenetic depth”? Here is the definition, as written by Nelson himself and published online, at ISCID:
Ontogenetic depth is a measure of the distance (in terms of cell division and differentiation) between a single-celled state and an adult animal (metazoan) capable of reproduction. All animals begin their existence as a single cell, the fertilized egg. From that cell, many other cells arise, and become specialized for particular functional roles—for instance, as sensory organs, skeletal parts, or reproductive structures (such as ovaries). The ontogenetic depth of any species measures the developmental distance between the starting point, the egg, and the stage at which organisms in the species can successfully reproduce themselves.
Developmental biology has mapped the ontogenetic depth of a handful of species, in the so-called “model systems” of the discipline, such as the nematode Caenorhabditis elegans or the fruit fly Drosophila melanogaster. To explain the historical origin of any animal species (and arguably the same is true for plants), one must give an account of how that species’ respective ontogenetic network—i.e., its process of differentiation—was constructed.
Unfortunately, I don’t have a lot to go on here. “Ontogenetic depth” has not been published in any peer-reviewed journal, I have not attended any of Nelson’s presentations on the subject, there are no methods described that would allow me to measure this value in any organisms, nobody other than Nelson and his collaborator, Marcus Ross, do anything with the idea, and all I’ve got are a transcript of an online chat and an accompanying pdf summary. It’s enough, I suppose. It’s clear that this is a poorly expressed and unusable idea based largely on misconceptions and faulty scholarship, with no actual research to back it up. I feel sympathy for Mr Ross, who has been suckered into an extraordinarily bad idea early in his academic career.
So what’s wrong with “Ontogenetic depth”?
It’s an unworkable idea. Nelson claims that ontogenetic depth is precisely measurable in extant species, and is therefore a good metric (“The ontogenetic depth of a handful of extant animals (from the model systems of developmental biology) is known with precision”). Unfortunately, this is simply not true. The sole example he gives is Caenorhabditis elegans, which has an exceptionally well understood pattern of stereotyped cell lineages that lead to the adult. This is not the case for other metazoans, and it’s not simply because they have cells too numerous to count; it’s also because most other animals don’t have an invariant cell number. Even in C. elegans, Nelson has to say that the ontogenetic depth is somewhere between 7 and 9…so much for specificity (and so much for measuring developmental differentiation—the mysterious unitless number doesn’t seem to describe the elegant precision of the nematode at all well).
It uses false assertions and confusing examples. The basis of Nelson’s claims about the relevance of ontogenetic depth to evolution are simply wrong. He tries to argue that changes to the early lineage of organisms are “wreckers”, that is that they are never viable, and therefore that patterns of early division can never change. He says,
When I was writing my dissertation, I asked one of my advisors if he knew of any cases of the heritable modication of early development . He couldn’t think of a single example (other than a change from left-to-right shell coiling, or back again, in snails—the exception that proves the rule).
This is confusing in several ways. Nelson spends a fair amount of time discussing the highly ordered cleavages of C. elegans. Is he, and his advisor, really unaware of the many known mutations in that organism that change the lineages? It’s a whole grand class of numerous mutations named lin; there are mutations that block subsets of divisions, add extra divisions, transform the pattern of one set of divisions to resemble another lineage, or change the timing of divisions.
And why is he even mentioning the direction of spiral cleavages in molluscs here? That’s a change in the chirality of early divisions, not any change in the pattern of divisions themselves. I don’t see that the orientation of divisions is even considered in his measurement of ontogenetic depth.
When he claims that changes in early divisions are invariably deleterious, I know that that is false from personal experience. The zebrafish embryos I work with have a canonical pattern of early divisions, but the animals can tolerate a significant amount of variation; heat shock or just spontaneous screw-ups can produce wacky cleavages, but the animals regulate and recover. Also look at what can be done with mammalian embryos: the inner cell mass can be dissociated, cells juggled around, and reassociated in part or in combination with other embryonic cells, about as thorough a scrambling of the pattern of early development as you can get, and the embryos can resume development normally.
It is also curious that Nelson discusses nematodes, cites Schnabel (1997), and manages to completely ignore that paper to claim that nematode lineages are absolutely fixed. Here is the abstract to that paper:
C. elegans is renowned for its invariant embryogenesis and functions as a major paradigm for a mode of development coupled to an invariant lineage. Recent work, however, suggests that the embryogenesis of the nematode is much more flexible than anticipated. The invariant premorphogenetic stage is formed from variable earlier stages through a sorting of cells. Cells do not act as individuals but already early in embryogenesis a regionalization of the embryo occurs. Cells are diversified by a binary specification of ‘abstract’ blastomere (regional) identities. The determination of tissues may thus be a very late event. It appears that C. elegans, although assigning cell fates in an invariant lineage pattern, uses the same strategies and mechanisms for embryogenesis as organisms with variable lineages.
Schnabel R (1997) Why does a nematode have an invariant cell lineage? Semin Cell Dev Biol 8:341-349.
It’s as if he read the title, copied one of the figures, and didn’t pay any attention at all to the conclusions of the paper, which contradict what he claims.
The idea is based on bad metaphors. Oh, jeez, Nelson’s “Marching Band” metaphor…where to start? He tries to explain development as something similar to what a marching band has to do to assemble formations on a playing field: individual bandmembers (cells) have to maneuver through a series of defined steps (development) to end up in a position that spells out something (the adult state).
This is not how development works.
Cells do not, in most cases, have a pre-programmed pattern of differentiation built into them, that they then follow rigidly to end up in a specific, fated state or position. Development is about flexibility, interaction, negotiation, and emergent properties. To state that a trumpet player who doesn’t know his rules would lead to the college’s name getting misspelled on the football field doesn’t say a thing about whether changes in development are impossible. In many organisms, we can shoot the trumpet player, blindfold the clarinetists, tumble everyone around in a cement mixer, and add a gang of bagpipe-playing soccer hooligans, and the mess can still organize itself to spell out a message (probably not a polite message, but something coherent, at any rate). If Nelson wants to make a metaphor, it’s going to have to be one that can account for the radical regulative reorganization that has been observed in real developmental biology.
The only way I can imagine Nelson would even propose such a bad model is that he is both unaware of the range of processes in development, and that he has been misled by exaggeration and mischaracterization of the processes in many of the most common model systems. One worrisome flaw in molecular developmental genetics research is that we rely on simple laboratory models—nematodes, fruit flies, zebrafish—that are not well representative. These animals all develop very rapidly and are relatively simple, which is convenient for research, but unfortunately means that they tend to be developmentally streamlined, with less redundancy and more inflexiblity than is good for us. Biologists also tend to look for changes with large-scale, robust effects, further biasing our knowledge of what kinds of changes are out there. Nelson has taken a sampling bias that we are aware of (and that he should be aware of, too; he cites Raff, who has discussed the problem in some detail in his book, The Shape of Life) and exaggerated it to a cartoonish degree. We know that our models bias our perception of development in a certain direction. Nelson has taken a bias and blown up the error into a natural law.
There is no research! Ontogenetic depth is a sloppily-defined concept with no theoretical support for its validity and no apparent operational utility. What can a scientist do with it? Nelson has a plan:
However, it should be possible, using modern analogues for fossil taxa—e.g., the extant monoplacophoran Neopilina for the extinct mollusc Scenella—to obtain good estimates on the ontogenetic depth requirements of many Cambrian forms. This is research we are now conducting. It is likely that reasonable estimates of the ontogenetic networks, and depth, required to specify such extinct organisms as Anomalocaris or Opabinia, will require no less complexity than that of modern animals.
To which I can only say, “what?”
He doesn’t have a way to measure ontogenetic depth…at least, not any way that he has explained, and that can be justified.
There is no reason to think that this parameter even describes complexity better than, for instance, counting cell types at maturity, which is also a fuzzy and difficult job.
If you determine (in some way) that this modern mollusc is as complex as another modern mollusc, how can you then claim that that means that ancient molluscs were as complex as modern ones? Isn’t that already your assumption when you claim that the modern form is an analogue of the extinct one?
We already know that the Cambrian fauna were complex. I don’t quite see what we’d learn that would be new to have someone announce that they have invented a new metric (which doesn’t seem very good) that shows that the Cambrian fauna were complex.
I don’t think he is necessarily measuring complexity, so it’s even worse. What do we learn from carrying out a convoluted process to determine that some animal in the Cambrian weighed 50 grams and had 1010 cells, and some other animal in the present day weighs 50 grams and has 1010 cells?
The actual goal of Nelson’s ‘research’ is to conclude that developmental complexity is infrangible, and that if he shows Cambrian organisms to be complex, that it is therefore impossible for them to have evolved. One of his cheerleaders, Tristan Abbey, makes this explicit:
But that can’t be true! The earliest stages of development are different among the various animal groups. They must have evolved somehow. But how? If development can’t be touched, how did it change?
The simplest answer for IDists is that it didn’t.
Nelson’s research program seems to be counting cell divisions in extant organisms, and leaping to the unsupported conclusion that evolution is impossible if he gets similar numbers in two different groups. That conclusion is what is unsupported and untested by his methods. No one other than a few uninformed Intelligent Design creationists are claiming that “development can’t be touched”.
Those anecdotes… One last minor point. What is it with all these ID creationists and their little quotes from China? Wells does it, now Nelson does it:
I had with me (on top of my conference files) an overhead transparency, showing the complex regulatory sequence of an invertebrate developmental gene.
And up walked the author of that very paper (a visiting American biologist), from which I had borrowed the figure.
Of course he spotted the diagram right away. “What do you plan to do with that?” he asked me.
“I thought I might use this in my talk,” I said, “as a quick illustration of the complexity of embryonic regulation.”
The biologist smiled. Knowing that he was something of a critic of neo-Darwinism, I asked him what historical process he thought had assembled the complex regulatory sequence.
His answer really surprised me. “I don’t know,” he said, “but I do know that ordinary mutation and selection won’t do it.”
He went on to say that he thought our (that is, the biological community’s) understanding of evolution lagged way behind its other knowledge.
An unattributed quote from a mysterious biologist attending a Discovery Institute sponsored meeting does not impress me in the slightest. I would like to know what a non-ordinary mutation might be, and why anyone should be surprised that a modern evolutionist would suggest that there is more to evolution than selection.
Reading Nelson’s proposed research was rather like reading a very poor preliminary exam proposal from an unpromising graduate student. It would be grounds for flunking the poor sap out of the program on the spot. It’s certainly not publishable, nor does it even hint at the potential for being publishable. And it’s probably the best piece of work to emerge from the Intelligent Design crowd yet, which should give you an idea of the low quality material they’ve got.
This is off topic and I apolgise for that but according to HBO Richard Dawkins will be on Real Time With Bill Maher nest week.
Eagle eyed readers will re-call I mentioned this around about the time Richard went to see “Expelled”.
His name was on the guest schedule but he was not on the show for some reason. Lets hope he gets on this week!
http://www.hbo.com/apps/schedule/ScheduleServlet?ACTION_DETAIL=DETAIL&FOCUS_ID=659186
That should be next week. Sorry
Wow! Send out a press release. PZ is actually trying to talk about science.
These reposts normally mean they’re setting up a new post. Does this mean Nelson has finally published the detailed explanation of ontogenetic depth that he promised?
I’d give them credit for trying if they really were. I’m not sure I want to be that generous, though. His entire premise relies on a claim that is known to be not true (the unvarying process of development in complex organisms, something that everyone who only gets their science from the CSI chimera episode knows is mistaken). It appears that the error comes in part from the anti-evolutionists’ commitment to their ‘special understanding’ of information theory and their misguided attempt to apply it to genetics.
At some point, analogies like “genes are the blueprints of life” are recognized by scientists as nonsense, even if they are a useful shorthand to help explain things to the averagely bright ignorant layman. The difference between real science and DI ‘science’ is that no scientist is trying to develop a research project from an analogy that is known to be misleading at a fundamental level.
It is also not evident that Nelson understands feedback controls of any sort. In mathematics, one can develop a problem that has a specific answer. In the physical world, things vary, sometimes a lot, yet still manage to survive because there are controls that redirect the processes into a successful result. Sure, some events can cause the system to fail, but that doesn’t matter much to organism development over the generations since catastrophic failure tends to stop development.
I wonder if 42 is the maximum Ontogenetic depth.
On the bright side, at least Nelson has done tons more work than either Behe or Dembski put together.
This is a great example of pseudoscience. He tries to sound scientific, but let’s compare it to the pseudoscience checklist:
1. The tendency to propose scientific theories that can’t be empirically tested in any meaningful way
Being that his claims and units are not specific, it can’t be meaningfully tested.
2. The dogmatic refusal to give up an idea in the face of overwhelming evidence that it’s false
Number two, thy name is ID.
3. Selective use of data
Oh yeah. Big check here.
4. The use of personal anecdotes as evidence
Sure. It’s the unnamed biologist thing.
5. The use of myths or ancient mysteries to support theories, which are then used to explain the myths
Well ID tries to disguise this, but of course it’s their main characteristic.
6. Claims of conspiracy theories to suppress their data
See the movie Expelled.
Yup, this is pseudoscience, no doubt about it.
Jumpin’ Jeezus, even I can (vaguely) understand that this proposed methodology is flawed on several levels!
And what the feck is “heritable modication”? Even if it should’ve been “heritable modification”, the paragraph doesn’t seem to make sense, in terms of its grammatical construction. If that’s the level of English usage this guy’s capable of, it doesn’t give one much confidence in him, eh. Maybe, as a non-biologist, I’ve missed the point somewhere?
“PZ Myers: Because purveyors of pseudoscientific claptrap need a good spanking.”
Between you and the Pharyngula commenters, I feel that the world will one day again be safe for science. Now we just need to get you guys a tv show…
PZ. I thought Pirates didn’t like sharks. You did a great job as a shark on this one. “Ontogenetic depth” looks like another IDiot invention that will never go anywhere. I won’t hold my breath to see any published peer review paper using this term. The peer reviewers will laugh themselves to death. Keep up the good work I do enjoy reading these types of articles.
Aethist & Proud
DenisC
How would this approach deal with the parasites that have remarkably baroque life cycles? In many cases, these organisms can reproduce both sexually and asexually, depending on the stage in the life cycle, and that life cycle is often not a strictly linear sequence of stages. Which reproductive stage counts as “the stage at which organisms in the species can successfully reproduce themselves”, when there can be multiple distinct stages at which reproduction occurs?
And I take it this proposal leaves out unicellular life entirely, despite the fact that it is probably half the biomass of the planet?
Nelson is simply dressing up an old fallacy, Argument from Incredulity and Ignorance. “I can’t see how my foot evolved so god exists.”
This fallacy is at least 2,000 years old. ID hasn’t moved a lot in the last 2 millenia.
The DI isn’t even pretending anymore. They have gone totally political, Xian Dominionist propaganda machine. The Templeton foundation, which supported them with big bucks, dropped them and said, they don’t want to support “political organizations.”
Tulse said:
Maybe he feels that this is Behe’s area of *ahem* expertise? After all he wouldn’t want to go tramping around in a field he knows next to nothing about and make a fool of himself no would he.
oh, wait . . . . .
“Nelson has to say that the ontogenetic depth is somewhere between 7 and 9…”
I don’t necessarily want to help Nelson out but I will go ahead and do the math for him; I’d say, using his numbers for C. elegans, that the ontogenetic depth is approximately 8. Plus or minus…
Hey – no fair! Nelson left out Quantum Mechanics! Surely he could have added that in there somewhere.
I commented on a previous PZ post about ontogenetic depth, and since I remember putting a bit of thought into that comment, I think I’ll go ahead and repost it here. :-)
Science is not my field (though I suspect I could do a better job than most of these ID guys) but even without a lot of scientific knowledge, the logic in all these guys is so amazingly flawed. It’s one fallacy after another. Ignorance, false dichotomy, compositional, etc. ad nauseum. ID seems to me on par with Dianetics and astrology (which Behe apparently believes is worthy of the word “science.”
It never fails to amaze me that they try so hard to kick off their little movement by starting INSIDE science, and then try to break out of it. They take so many scientific staples for granted, such as genetics and the categorization of species, etc. Then, they use those assumptions to try and take the entire field of study in another direction. They bias their work against themselves, and then cry when it fails.
At the very least I will say, as a total science noob, that Nelson’s idea seemed attractive on some level, and appeared that it lend some level of insight. PZ promptly explained why it’s a bad one, and I have heard the marching band metaphor before amongst these pages. I am better informed on both counts, and I appreciate PZ’s generally dispassionate analysis through mmost of the post, and on the key points of discussion and issue.
But the problem for ID is still research, research, research. Bring the damn research. I guess I have too much shame, as I wouldn’t even attempt such a lightly constructed argument if I were in Nelson’s position. I would simply not even try.
In many organisms, we can shoot the trumpet player, blindfold the clarinetists, tumble everyone around in a cement mixer, and add a gang of bagpipe-playing soccer hooligans, and the mess can still organize itself to spell out a message (probably not a polite message, but something coherent, at any rate).
This made my day.
Science Pundit, “ovipoultricity” is definitely a keeper, and so versatile! “Getting some sort of universal health coverage in the US is a problem of intractable ovipoultricity.” I like it!
I mean, damn, how can Nelson not know? We learn this in second year in biology… I can hardly believe you can graduate in biology and never have heard about this.
Hell, dvizard, you can “major… in biological sciences in undergraduate work” without learning that the singular of “species” is *not* “specie”, so nothing surprises me any more.
Science Pundit,
As the problem, classically stated, is `chicken and egg` should the word not be `poultryovicity`?
As a lay person, I find “ontogenetic depth” not to be so much meaningless as simply useless. First off we know that “ontogeny recapitulates phylogeny” is not true, and it certainly seems like Nelson is basing his entire concept off that idea, or something very closely related. (If he isn’t, it’s extremely unclear what the hell he’s trying to prove — “ontogeny is phylogeny”?.)
Second, it doesn’t account for creatures such as Xenoturbella, the Myxozoa, HeLa, or the entire family of yeasts. All represent an apparent drastic simplification of a more complex life form (in the latter three cases, from a multicellular organism down to a single cell), which would certainly reduce the “ontogenetic depth” of the progeny. (While I realize the identification of HeLa as a species unto itself is highly controversial, it’s certainly an organism with absolutely no ontological resemblance to H. sapiens at all.) How does one look at such organisms, with clearly proved genetic relations to more complex species, and say that a measure such as “ontological depth” is of any use at all, except perhaps as part of a back-of-the-envelope description?
Perhaps Nelson should quit with Ontogenetic Depth, and go on to work with Ontological Depth, which is defined as “the measure of the distance between a single-celled state and the Necessarily Existing Essence of its Divine Creator.”
Is there a scale of cell differentiation branching pattern? This would be related to number of cell types, organismic complexity, modularity.
Seamyst,
Me too. I love to see a metaphor taken and run with like that.
Am I reading this wrong, or isn’t it unfair to subject Schnabel to the Comic Sans treatment?
Finally, a chance to use my hard-earned expertise!
Marching band members make formations by keying off of the yard markers on the football field, and by judging the distance between themselves and the band members on either side of them. They also use a standard stride length of 8:5 (eight strides to every five yards). Minor glitches in transitions can be easily corrected by adjusting the stride length.
It’s highly improbable that a single trumpeter could render the college name illegible. More likely is that a single letter might have a wobble in one stroke. And if you watch half-time shows, you see that that happens all the time, with no loss in information.
In a good marching band, the fact that you use yard markers, distance, and stride length together as redundant checks means that it’s mostly self-correcting. E.g., I turn 45 degrees to the left, march 15 steps to a point 3 paces past the 35 yard line, one arm’s length (parallel to the sideline) from that cute mellophone player I have a crush on. Even if the cute mellophone player steps in a divot left by some stupid jock and breaks stride, I can still key my position off of the yard marker and my stride length.
Even a catastrophic failure (e.g., turning right when you should turn left) would at worst result in a shape with one missing element, and the wayward trumpeter would be off to one side, a bit of statistical noise.
–Howard Peirce, lead trumpet, Haworth High School Marching Band, class of ’81
HP, that gets my vote for post of the day. =)
How can you applaud such a fowl term?
Sorry :o)
@thalarctos #22
Once, when teaching a lab, I asked some first year students to complete the experiment and then present their results in a table.
One of them asked me what a table was.
I think it says a lot for my patience that that particular individual is still alive today.
I doubt it, since it’s the only form of life for which this quantity appears to be well-defined, the ontogenic depth being, by definition, zero for unicellular organisms.
The obvious questions are: how does one compute/estimate this quantity in theory; how does one measure this quantity empirically; and what is the correlation between the predicted and measured values?
As a first step, I suggest that the predicted value of ontogenic depth be compared with experiment for australopithecus spiffarino.
Not Xenoturbella, which is a basal deuterostomian that eats clam eggs, not a drastically modified clam.
By not knowing about the DNA evidence and starting from the assumption that evolution hasn’t happened. In other words, by starting from one’s conclusions and making arguments from ignorance. Can you smell the stupid oxide now? :-)
P.S.: Death to the trumpet player. B-)
Not Xenoturbella, which is a basal deuterostomian that eats clam eggs, not a drastically modified clam.
By not knowing about the DNA evidence and starting from the assumption that evolution hasn’t happened. In other words, by starting from one’s conclusions and making arguments from ignorance. Can you smell the stupid oxide now? :-)
P.S.: Death to the trumpet player. B-)
Why doesn’t Nelson just define it this way:
Ontogenetic depth = average number of cell type differentiations from the time the zygote is first formed until the organism is an adult (averaged over all the cells of the body)
Thus for a liver cell we might have:
zygote cell –> type 1 –> type 2 –> liver cell (depth = 3)
For a neuron:
zygote cell –> type 1 –> type 2 –> type 3 –> neuron (depth = 4)
Let’s say the adult organism is 50% liver cells and 50% neurons (only for the sake of calculation). Then ontogenetic depth = 3.5. Not sure if this was the type of thing Nelson was thinking of, but it would at least in principle be computable even though in practice it would be very, very difficult to arrive at a final number.
so with phrases like intelligent design, irreducible complexity, specified information and now ontogenetic depth the ID bunch feel they have enough long words to confuse the gullible and make them love jesus that bit more.
Meh, I’m not surprised. Nelson never seemed that bright when he starred in Coach.
Bit of unwanted nostalgia: My HS marching band got the opportunity to play at a Pittsburgh Steelers game, national TV, etc. The director designed the most complicated show yet, involving a train locomotive with moving wheels or some such formation. Man, did we practice!
Gameday, a fellow trumpet player offers me half of a PB, J and weed sandwich, which (that being my wont in thoze daze), I ate. Halftime we were doing OK until the train formation (or whatever it was) when I made the proverbial wrong turn and led my squad (group of 4)–who followed obediently–in entirely the wrong direction. When I realized, I had to compensate with an entirely improvised snaking trek through the rest of the band to our correct spot. I don’t think we were on TV anyway.
We now return you to your regularly scheduled discussion of the non-concept of ontogenetic depth.
BlueIndependent @ 29: Do you play mellophone, by any chance?
Let’s say the adult organism is 50% liver cells and 50% neurons
Hey, that sounds like me during college. I never could have drunk so much and still have gotten a degree if it weren’t true.
What? A bunch of suckery, tearing tentacles and a razor-sharp beak not good enough??
Would my ontogenetic death change if I got cancer?
Okay. So I still don’t get it.
Ontogenetic depth = Time from conception through birth to puberty x arbitrary number?
Ontogenetic depth = Number of cells that ever lived in the individual to get it to puberty?
Ontogenetic depth = A whole load of guano?
I opt for the latter.
When are Paul Nelson and Rupert Sheldrake going to get together to flesh out the grand unified theory of Ontogenetic Resonance?
Combine two vacuous pseudotheories you’ll get something less than the sum of the parts.
I dated a band geek once. Didn’t really click though, so I can only appreciate said comments on a broad level.
David:
I knew Xenoturbella isn’t a mollusc (though I’ve heard about the controversy), but I was under the impression that it wasn’t actually a basal organism as such but one whose ancestors had undergone radical simplification (possibly by virtue of having been parasites that became free-living again).
Xenoturbella just happens to be one of my more favorite animals just by virtue of being very very weird…
Hmmm, if the number of cell divisions is what counts then birds are more complex than us mammals since they go for the ‘a lot of small cells’ way of building a body of size X while us mammals go for the ‘moderate number of moderate sized cells’ to do the same job.
I was made aware of this during my PhD thesis, I was counting all the myotubes from a developing mouse muscle while the chicken people doing similar stuff had to use sampling methods as chook muscle has a LOT of cells.
So, if
Unicellular = OD(0)
Does
Virus = OD(-1)?
Is there a correlation between number (total) of cells and cell types? Could we say OD(3) has three cell lineages and 1000 cells? That would work for single-celled organisms: 0 cell lineages or types, 1 cell (10^0 = 1)
So, working backwards, humans with trillions of cells (10^12) would have twelve cell lineages? Or is there a more complex formula I’m missing?
Math is hard!
“Is there a correlation between number (total) of cells and cell types?”
According to Stuart Kauffman in his 1995 book “At Home in the Universe”:
number cell types = square root(number of genes)
http://en.wikipedia.org/wiki/Stuart_Kauffman
Of course, Kauffman is not a creationist which means his predictions might actually pan out. However, from the data I have been able to gather on the Internet this particular numerical relationship does not appear to hold to any degree of accuracy in the biological world.
“Ontogenetic depth” is one of those ideas that sounds, to a person unfamiliar with the actual science, like a reasonable idea. People love to put meaningless numbers on things, then draw meaningless conclusions from those numbers.
I’m sure it will be the new “specified complexity” in terms of cdesign proponentsists hand-waving.
I expect to see something about it on my brother’s blog soon. I should preempt it, but am feeling a little too lazy right now.
David Marjanović:
It would still appear to be simplified, because it lacks features shared by “higher” deuterostomes and protostomes.
Ontogenetic depth – an icthyological concept:
Ontogenetic depth partitioning by juvenile freshwater sawfish (Pristis microdon: Pristidae) in a riverine environment
Author(s): Whitty JM (Whitty, Jeff M.)1, Morgan DL (Morgan, David L.)1, Peverell SC (Peverell, Stirling C.)2, Thorburn DC (Thorburn, Dean C.)1, Beatty SJ (Beatty, Stephen J.)1
Source: MARINE AND FRESHWATER RESEARCH Volume: 60 Issue: 4 Pages: 306-316 Published: 2009
Times Cited: 1 References: 42
Abstract: The freshwater sawfish (Pristis microdon) is a critically endangered elasmobranch. Ontogenetic changes in the habitat use of juvenile P. microdon were studied using acoustic tracking in the Fitzroy River, Western Australia. Habitat partitioning was significant between 0+ (2007 year class) and larger 1+ (2006 year class) P. microdon. Smaller 0+ fish generally occupied shallower water (<0.6 m) compared with 1+ individuals, which mainly occurred in depths >0.6 m. Significant differences in hourly depth use were also revealed. The depth that 1+ P. microdon occupied was significantly influenced by lunar phase with these animals utilising a shallower and narrower depth range during the full moon compared with the new moon. This was not observed in 0+ individuals. Habitat partitioning was likely to be related to predator avoidance, foraging behaviours, and temperature and/or light regimes. The occurrence of 1+ P. microdon in deeper water may also result from a need for greater depths in which to manoeuvre. The present study demonstrates the utility of acoustic telemetry in monitoring P. microdon in a riverine environment. These results demonstrate the need to consider the habitat requirements of different P. microdon cohorts in the strategic planning of natural resources and will aid in the development of management strategies for this species.
I don’t recall writing this …
oh …
This is a two year old thread …
Nevermiiiiind …