Chance and regularity in the development of the fly eye

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fly_eye_tease.jpg

What has always attracted me to developmental biology is the ability to see the unfolding of pattern—simplicity becomes complexity in a process made up of small steps, comprehensible physical and chemical interactions that build a series of states leading to a mostly robust conclusion. It's a bit like Conway's Game of Life in reverse, where we see the patterns and can manipulate them to some degree, but we don't know the underlying rules, and that's our job—to puzzle out how it all works.

compoundeye.jpg

Another fascinating aspect of development is that all the intricate, precise steps are carried out without agency: everything is explained and explainable in terms of local, autonomous interactions. Genes are switched on in response to activation by proteins not conscious action, domains of expression are refined without an interfering hand nudging them along towards a defined goal. It's teleonomy, not teleology. We see gorgeously regular structures like the insect compound eye to the right arise out of a smear of cells, and there is no magic involved—it's wonderfully empowering. We don't throw up our hands and declare a miracle, but instead science gives us the tools to look deeper and work out (with much effort, admittedly) how seeming miracles occur.

One more compelling aspect of development: it's reliable, but not rigid. Rather than being simply deterministic, development is built up on stochastic processes—ultimately, it's all chemistry, and cells changing their states are simply ping-ponging through a field of potential interactions to arrive at an equilibrium state probabilistically. When I'd peel open a grasshopper embryo and look at its ganglia, I'd have an excellent idea of what cells I'd find there, and what they'd be doing…but the fine details would vary every time. I can watch a string of neural crest cells in a zebrafish crawl out of the dorsal midline and stream over generally predictable paths to their destinations, but the actions of an individual melanocyte, for instance, are variable and beautiful to see. We developmental biologists get the best of all situations, a generally predictable pattern coupled to and generated by diversity and variation.

One of the best known examples of chance and regularity in development is the compound eye of insects, shown above, which is as lovely and crystalline as a snowflake, yet is visibly assembled from an apparently homogenous field of cells in the embryo. And looking closer, we discover a combination of very tight precision sprinkled with random variation.

Continue reading "Chance and regularity in the development of the fly eye" (on Pharyngula)

67 Comments

PZ,

Another fascinating aspect of development is that all the intricate, precise steps are carried out without agency…It’s teleonomy, not teleology.

I thought PT’s whole shtick was that teleology is philosophy and, therefore, it doesn’t belong in science. Apparently that’s just a cover for a priori excluding design in order to better sell your atheistic worldview. The gig is up!

Thanks for the fascinating post, PZ.

Sorry, however, not to have gotten that comment up before the first mouth-breather defaced the thread. Ah, well.

For those who do know how to read:

TELEONOMY: the element of apparent purpose or possession of a project in the organization of living systems, without implying any vitalistic connotations. Frequently considered as a necessary if not sufficient defining feature of the living organization.

Steviepinhead,

I read the article and I know what teleonomy means.

PZ does a fine job of manipulating words like “chance” and “randomness” to imply “purposelessness”. I tend to agree with quantum physicist Henry Stapp’s assessment: “Chance is an idea useful for dealing with a world partly unknown to us. But it has no rational place among the ultimate constituents of nature.”

The role of manipulating chance and randomness to imply purposeness has been assigned to the Intelligent Design movement. Did you not get the memo?

What PZ shows is that the concept of design or teleology is complicated by the fact that chance and regularity appear to be sufficient. In other words, the eliminative approaches sought by ID are once again found to be vacuous.

You and Stapp can think whatever you like. If you want to call that philosophizing, then indulge your penchant.

Do let us know when you have any actual evidence for the larger propositions you have put forth here, i.e.:

“The gig is up!”

“ ‘Chance is an idea useful for dealing with a world partly unknown to us. But it has no rational place among the ultimate constituents of nature.’ “

Oh, and be sure to let us know what evidence you have that physicist Stapp was addressing emergent phenomena like biology when he was propounding upon the “ultimate constituents of nature.”

Needless to say, I won’t be holding my breath awaiting a reply that actually contains evidence for these hallucinations qualia of yours.

I don’t get it – Qualiatative is being self-defeating. So he wants to argue that there is some “purpose” behind the fact that a rhabdomere 2 ommatidia in from the posterior margin, 3 ommatidia down from the equator, is expressing Rh3 in Fly Alpha, and some other purposeful reason why the equivalent rhabdomere in Alpha’s sister, Beta, is expressing Rh4?

That is remarkably stupid.

PvM,

the eliminative approaches sought by ID are once again found to be vacuous.

ID, as I understand it, is not committed to everything in nature being the direct product of intelligence.

Steviepinhead,

Do let us know when you have any actual evidence for the larger propositions you have put forth here, i.e.: “The gig is up!”

I was being facetious here. PZ will, in all likelihood, be ranting until the day he days.

Oh, and be sure to let us know what evidence you have that physicist Stapp was addressing emergent phenomena like biology when he was propounding upon the “ultimate constituents of nature.”

Accounts of causality are inherently metaphysical. Thus, PZ’s attempt to use biology to demonstrate purposelessness on a “scientific level” is non sequitur. Ultimately, randomness only reflects our ignorance of the underlying system.

PZ,

I am not the one making philosophic inferences here. It seems to me that you are advocating “randomness” as an irreducible constituent of nature. Is this true?

PZ:Except us developmental biologists, of course: the fly eye is an extremely well studied developmental system, and we know that it is assembled by unthinking cellular processes with no design or engineering required.

Except that no one ever said that flies are thinking with their eyes or that they think their own eyes into existence.

I know, it’s all a little bewildering and complicated—intensely complicated with all kinds of interactions between cells.

Apparently Myers got out his special smarty pants that Mother Nature gave him, just for this post. It was probably her natural selection again.

Fortunately for any without naturally selected smarty pants Myer’s own text just so happens by quite a happenstance to be assembled by unthinking cellular processes. Given a little historical narrative about how his text came to be (Darwinists shouldn’t object to that!) his few attempts at a mixture of his personal philosophy about “unthinking cellular processes” in it probably reduce to neurosis derived from personal history, a sort of cosmic Oedipus complex that is typical to certain fellows.

However, when you dig into it and explore the literature, what you find is the successful application of a reductionist program of study, with each piece of the story a fully comprehensible and actually rather simple product of a molecular/cellular interaction.

Molecular/cellular? Even for those with the urge to merge blurring the difference between molecules and cells is pushing it.

ID, as I understand it, is not committed to everything in nature being the direct product of intelligence.

Indeed, it merely limits it to that which we do not yet understand. But remember that ID is also proposing to move the initial injection of ‘information’ to a front loading event such as perhaps the Big Bang. As long as ID relies on eliminative approaches exclusively, it will fail to be scientifically relevant.

Accounts of causality are inherently metaphysical. Thus, PZ’s attempt to use biology to demonstrate purposelessness on a “scientific level” is non sequitur. Ultimately, randomness only reflects our ignorance of the underlying system.

And ID seems to be willing to take the place of randomness by arguing that our ignorance should be evidence of design.

I am not the one making philosophic inferences here. It seems to me that you are advocating “randomness” as an irreducible constituent of nature. Is this true?

Hi Bill…

But yes, randomness IS an irreducible constituent of nature. Or at least at the quantum level that is what it appears to be. What better place for an Intelligent Designer (wink wink) to hide than in the ‘randomness’ of the quantum world. Next we can imagine the designer to use an infinite wavelength channel to communicate. Oops forgot that the bandwidth becomes zero. Back to the drawing boards

An interesting question: Is randomness an irreducible component of nature or is randomness reducible to deterministic forces?

One may be tempted to argue that randomness is real due to the chaotic nature of nature but chaos could be due to our inability to measure the relevant parameters continuously. In other words, randomness in chaos could be reduced to determinism IFF we had sufficiently accurate data.

More later

So he wants to argue that there is some “purpose” behind the fact that a rhabdomere 2 ommatidia in from the posterior margin, 3 ommatidia down from the equator, is expressing Rh3 in Fly Alpha, and some other purposeful reason why the equivalent rhabdomere in Alpha’s sister, Beta, is expressing Rh4? That is remarkably stupid.

So you wouldn’t agree that the purpose of the unfolding of events that you trace back to “chance” is for the eye to see?

I wonder, how does the Blind Watchmaker make things to watch it? I suppose that we should keep watch on her to make sure that she keeps time with us. After all, as Myers has now proven the flies with their unthinking eyes probably will not keep watch.

“But you don’t seriously believe,” Einstein protested, “that none but observable magnitudes must go into a physical theory?” “Isn’t that precisely what you have done with relativity?” I asked in some surprise. “After all, you did stress the fact that it is impermissible to speak of absolute time, simply because absolute time cannot be observed; that only clock readings, be it in the moving reference system or the system at rest, are relevant to the determination of time.” “Possibly I did use this kind of reasoning,” Einstein admitted, “but it is nonsense all the same. Perhaps I could put it more diplomatically by saying that it may be heuristically useful to keep in mind what one has actually observed. But on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality the very opposite happens. It is the theory which decides what we can observe.”

(Physics and Beyond by Werner Heisenberg trans. Arnold J. Pomerans (New York: Harper & Row, Publishers, 1971) :63)

That will not make sense to some. I leave it to inverts to relegate themselves to being a useful heuristic.

PvM,

Hi Bill…

I’m flattered but you are mistaken. I believe philosophic inferences involving causality should remain in philosophy.

But yes, randomness IS an irreducible constituent of nature. Or at least at the quantum level that is what it appears to be.

Now do you see why I quoted a quantum physicist?

How remarkable. Usually, my science posts get almost no comment…I’d forgotten, though, that the word “random” throws creationists into such a tizzy.

Look at the title, you silly illiterates.

“Chance and regularity in the development of the fly eye”.

Chance is involved in the determination of photoreceptor types. It’s absurd to argue otherwise.

Regularity is also involved – there are specific rules and patterns of interaction that set up the arrangements of rhabodmeres.

I’m certainly not arguing that everything in biology is just random noise. You’d have to be a major idiot to assume that.

It’s also eminently clear that biology is not purely determinate.

Qualiative and mynym: what are you guys, some kind of dolts?

PZ,

I can engineer systems of dots in Conway’s Game of Life that will spawn a potentially infinite series of generations. As the game flickers to proceeding generations the change could be misconstrued by a passive observer as “random”. Yet we know that the game is contingent upon initial conditions acted upon by a repetition of rules.

So what is “random”, PZ? Is it irreducible? Is it patterned determinism? Or is it something else?

Qualiatative wrote:

I tend to agree with quantum physicist Henry Stapp’s assessment: “Chance is an idea useful for dealing with a world partly unknown to us. But it has no rational place among the ultimate constituents of nature.”

That’s only true in the sense that whether it’s random or predictable (it could be a regular algorithm which some “random” number generators are) doesn’t change the outcome. What is needed is a source of variation – almost any source will do. The fact that it can be random (or a simple minded algorithm) eliminates the need for an intelligence to supply the variation. The creativity and designing engine is in the selectionism working on varied outputs, not in the variation.

Now do you see why I quoted a quantum physicist?

Who?

“Now do you see why I quoted a quantum physicist?”

Not by any chance (oops I mean Design - there is no chance) a screwball one with his own version of QM?

In any case much is chance so far as the organisms are concerned.

Syntax Error: mismatched tag at line 1, column 124, byte 124 at /usr/local/lib/perl5/site_perl/5.16/mach/XML/Parser.pm line 187.

Qualiataliatedive, Dork, it’s “jig” not “gig”. You know, I have all the info you need on my blog.

Posted by Qualiatative on March 20, 2006 09:38 PM (e)

PZ,

I can engineer systems of dots in Conway’s Game of Life that will spawn a potentially infinite series of generations. As the game flickers to proceeding generations the change could be misconstrued by a passive observer as “random”. Yet we know that the game is contingent upon initial conditions acted upon by a repetition of rules.

So what is “random”, PZ? Is it irreducible? Is it patterned determinism? Or is it something else?

Dork, you are calling this fractal geometry or chaos or continuous phase transitions or something. If you throw a stick in a creek, are you designing the ripples? You are religious and stupid. Please keep quiet and let others speak for you.

I have a question for ‘Qualiatative’ and Mynym. How come ID trolls who come here never talk to each other? You guys all pretend like the other trolls aren’t here. You guys are all trying to defeat ‘methodological naturalism’, shouldn’t you stick together? Or are you maybe embarrassed by your fellow trolls?

Let’s give Qualiatative a chance

ID, as I understand it, is not committed to everything in nature being the direct product of intelligence.

So, according to ID, what are some things in nature that are the direct product of intelligence, and what are some things in nature that are NOT the direct product of intelligence?

Examples from biological nature would be greately preferred. Extra bonus points for examples of different parts of the same organism (i.e. species).

And for a specific intelligent product and a specific non-intelligent product, what is the particular calculation that demonstrates the difference between them?

As a larger point, is there any rhyme or reason for the distribution of intelligent products and non-intelligent products among organisms? For example, if the eye is intelligently designed, does it follow that the eyelid is intelligently designed? What about the eyebrow?

Or if the blood-clotting mechanism is intelligentlly designed, can we infer that blood vessels (which blood clotting seal up when they’re torn) are intelligently designed also? If not, doesn’t it seem unlikely that animals would exist with blood circulation systems but not blood clotting, only to be helped out by an Intelligent Designer who came along later with a fix-it mechanism for their blood vessels?

PZ,

I appreciate what you have written, carefully qualifying your assertions and comments. I can tell that you are passionate about science.

Wouldn’t it be neat if there existed a decent simulation of some complex biological process, with sufficient fidelity to show behaviour consistent with observation? I am not talking about microscopic systems such as 1,000 water molecules, or even the folding of a large protein. Rather, how about, say, a complete simulation of a small ecosystem based on Caenorhabditis elegans, the tiny worm that some people spent years studying in excruciating detail? (“In the beginning was the worm,” Andrew Brown, Simon and Schuster, 2003.)

Such a simulator has not yet built, nor may it ever get built, if people lose interest in C. elegans as a model organism. However, wind the clock forward 1,000 years and who knows what science will have at its disposal? Perhaps then there might exist something akin to a “mathematical proof” of the detailed origin and explanation of some complicated biological process such as evolution in action within a colony of nematodes?

Still, I wonder what the future creationists will make of such a “proof”. I suspect they will bang their war drums as loudly as ever before, and refuse to acknowledge such proof as may exist.

It’s funny how nobody, creationist or scientist alike, would fault the solution I will give to a simple problem:

PROBLEM: Find the number y that makes the following assertion true …

2y-4=0

SOLUTION: y = 2

No creationist will dispute this, as it has nothing to do with religion. This does not challenge any cherished notions. Even if I got the solution wrong, nobody’s blood would boil. The most hardened advocate on either side of the fence would simply scoff at me, and nothing much more than that. But say something that threatens to step on the toes of that holiest of holies, GENESIS, and look out … real listening stops and the argumentum ad hominem begins in earnest.

Arden Chatfield Wrote:

How come ID trolls who come here never talk to each other? You guys all pretend like the other trolls aren’t here. You guys are all trying to defeat ‘methodological naturalism’, shouldn’t you stick together? Or are you maybe embarrassed by your fellow trolls?

C’mon now. Surely you have heard of the pseudoscience code of silence. They are “sticking together” by their silence. What they should do is debate each other on their respective positions as “evolutionists” do with each other. Even YECs and OECs used to do that until the “don’t ask, don’t tell” ID strategy came along to discourage it.

Apparently that’s just a cover for a priori excluding design in order to better sell your atheistic worldview.

But ID isn’t about religion. No sireee Bob. Not at all. It’s just those lying atheist darwinists who say it is.

Thanks for (once again) demonstrating so clearly that (1) ID is just religious apologetics, (2) IDers are lying to us when they claim it’s not, and (3) Judge Jones was entirely correct when he concluded that it was.

This is why I love fundies so much – they are by far their own worst enemies. No matter how long they rant and rave that ID is science and has nothing to do with religion, just let them talk long enough, and every single one of them will shoot themselves in the head sooner or later, by shouting “Jesus saves!!!” at the top of their lungs.

Not only CAN’T they keep quiet about their religious motives and goals, but they don’t WANT to.

It’s why ID will never see the inside of a science classroom.

ID, as I understand it, is not committed to everything in nature being the direct product of intelligence.

Um, how do you propose we determine which are and which aren’t?

BTW, what the heck *does* ID commit itself to? ID seems to me to try, very very hard, never to actually say anything at all.

Qualiatative Wrote:

I read the article and I know what teleonomy means.

Really? Then why did you criticize it for its teleology? I’m guessing soreheaded creationist style sour grapes, but I could be wrong.

PZ does a fine job of manipulating words like “chance” and “randomness” to imply “purposelessness”.

Well, PZ sure fooled me. Can you be explicit?

I tend to agree with quantum physicist Henry Stapp’s assessment: “Chance is an idea useful for dealing with a world partly unknown to us. But it has no rational place among the ultimate constituents of nature.”

Yes, and Einstein said the same thing. So what? In what sense is it “rational” to reject one of the best and stunningly accurate of all the sciences? Neither Einstein, Stapp or numerous other quantum physicists have ever articulated a reason (as opposed to a feeling) to reject chance as an ultimate constituent of nature.

Where has the definition that you refer me to been published in the peer reviewed literature as the scientific theory of evolution?

man, you are dumb.

this is just like asking the question:

where do we find the definition of the modern theory of meteorology published in the peer reviewed literature?

A theory encompasses multiple hypotheses, correlates, and lines of evidence; it includes all of the history of experiment in testing relevant predictions. you won’t find a “definition of the entire theory of evolution” just like you won’t find a definition of all of quantum theory in a peer reviewed article.

the Modern Synthesis (the current ToE) is a theory about how evolution works at the level of genes, phenotypes, and populations whereas Darwin was concerned mainly with organisms, speciation and individuals.

However, you can start with Origin of species as the first peer reviewed publication, then you might try look at RA Fisher’s seminal publications relating to the formation of the more modern synthesis.

or hell, you could just go to any of the links on the front of PT and find the information you “seek”.

I’m sure you really aren’t interested in the “truth”, though.

In that case, er,

Just keep shakin’ that fist harder, boy!

Hmm. Let’s recap: your agenda here is to further the cause of a reactionary religious establishment…

The religious establishment has never had much of a problem with Darwinism,

How nice. Evangelicals and conservative Christians have now dropped their objections to ‘Darwinism’? Cool, must have happened when I wasn’t looking. Guess we can all go home now.

We’re talking about the last 20-30 years, genius.

if it had then Darwinism would have never been accepted. See the book Darwin’s defenders, it probably should have had more of negative attitude to Darwinism

Not everyone shares your hostility to empericism.

…and to reverse the last 100+ years of scientific learning…

The last 100+ years, eh? Would you include the eugenics movement in that, or just everything that you currently think is beneficial or progressive? It would seem that most who believe in scientism these days include every single advancement, all technology and all that is good and right under the term “science.”

Let me guess: Darwin caused Adolf Hitler, right?

A pathetic strawman argument, which I’ll do you the favor of ignoring, tho I can see you don’t spend much if any time among people ‘who believe in scientism’.

…and replace it with unchangeable 2,500 year old religious dogma.

If you think that religious dogma has not changed then you’re ignorant of religion.

I’m sure the Book of Genesis is a very dynamic document.

And this makes you some kind of iconoclastic ‘rebel’.

I never claimed to be anything. I’ll run with a herd if there’s a good herd to run along with.

So running with the herd is good if you like the herd. Otherwise it’s bad. Swell.

If you want to see ‘urge to merge, running with the herd’, I suggest you check out Uncommon Descent.

What do you expect, they’re beginning to form their own community.

Yes, with DaveScot forcibly evicting all dissenters.

It’s the establishment’s lose because ID is a tool that is already in use

By who, preachers?

that only needs to be formalized so that it can be used even more.

Ho ho. Yeah, you guys get right on that. So far ID consists of nothing more than “some stuff sure looks designed”. You can start by ‘formalizing’ it to deciding whether the earth is 5,000 or 4.5 billion years old, and whether the ‘designer’ was God or space aliens. And then everything else after that.

In the end, no one is going to care what is called “scientific” as long as it works.

Please offer your evidence that ID ‘works’. You’ll be the first one.

Ya know, thinking about “evolutionists” “running with the herd”, I’ve thunked up a hypothesis as to why that might be the case:

Consider several people who pay attention to reality, and then describe the same aspect of nature.

I hypothesis that while they may use different phrasing, what they say is quite likely to sound like it’s describing the same stuff.

Henry

Hey Mynym, would you mind explaining to me what the scientific theory of ID is?

In the instance I have in mind it would be taking a specification or definition of what you think a work of malevolent intelligence would look like in patterns of information and then testing if the data for it. I don’t really care if you call that scientific or not, as long as the results are correct and the pursuit of truth is furthered.

OK, so there isn’t any scientific theory of ID. Got it. Thanks. It’s what I suspected.

Mynym is like Homer Simpson in that episode where he was trying to be a hippy. “Never fear, the Cosmic Jester is here!”. He thinks he’s freaking with people’s minds and being really profound. Everyone else just thinks he’s annoying. And smelly.

mynym Wrote:

What’s the scientific theory of evolution?

“Natural selection” - according to your strawman anyway.

Chance is involved perhaps for no other reason that it is just a word that you are using as a sort of chance-of-the-gaps, a term that is slapped on any complex state of flux and the like in which the chain of cause and effect is not currently “understood.” - ID is a tool that is already in use that only needs to be formalized so that it can be used even more. In the end, no one is going to care what is called “scientific” as long as it works.

Considering these statements, you should be able to easily answer the following question: If what we think of as chance in a given process is really the meddling of a god, how could you tell? But perhaps you have already answered:

In the instance I have in mind it would be taking a specification or definition of what you think a work of malevolent intelligence would look like in patterns of information and then testing if the data for it. I don’t really care if you call that scientific or not, as long as the results are correct and the pursuit of truth is furthered.

Not only is that not scientific, it isn’t even coherent. It is incapable of producing results, correct or otherwise. You should work for the DI.

Why am I not surprised that mynym has failed utterly to engage with the literature on randomness even when prodded? Another ignorant creationist, for sure, if I can be forgiven the redundancy.

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This page contains a single entry by PZ Myers published on March 20, 2006 5:43 PM.

Evolution for Kids was the previous entry in this blog.

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