…and this is a 
On Thursday, I gave a talk at the University of Minnesota at the request of the CASH group on a rather broad subject: evolution and development of the nervous system. That's a rather big umbrella, and I had to narrow it down a lot. I say, a lot. The details of this subject are voluminous and complex, and this was a lecture to a general audience, so I couldn't even assume a basic science background. So I had to think a bit.
I started the process of working up this talk by asking a basic question: how did something as complex as the nervous system form? That's actually not a difficult problem — evolution excels at generating complexity — but I knew from experience that the first hurdle to overcome would be a common assumption, the idea that it was all the product of
purposeful processes, ranging from adaptationist compulsion to god's own intent — that drive organisms to produce smarter creatures. I decided that what I wanted to make clear is that the origin of many fundamental traits of the nervous system is by way of chance and historical constraints, that the primitive utility of some of the things we take for granted in the physiology of the brain does not lie in anything even close to cognition. The roots of the nervous system are in surprisingly rocky ground for brains, and selection's role has been to sculpt the gnarly, weird branches of chance into a graceful and useful shape.
So I put together a talk called The Ubiquity of Exaptation (2.7M pdf). The barebones presentation itself might not be very informative, I'm afraid, since it's a lot of pictures and diagrams, so I'll try to give a brief summary of the argument here.
The subtitle of the talk is "Nothing evolved for a purpose", and I mean that most seriously. Evolved innovations find utility in promoting survival, and can be honed by selection, but they aren't put there in the organism for a purpose. The rule in evolution is exaptation, the cooption of elements for use in new properties, with a following shift in function. It's difficult to just explain, so I picked three examples from the evolution of the nervous system that I hoped would clarify the point. The three were 1) the electrical properties of the cell membrane, which are really a byproduct of mechanisms of maintaining salt balance; 2) synaptic signaling, which coopts cellular machinery that evolved for secretion and detecting external signals; and 3) pathfinding by neurons, the process that generates patterned connectivity between cells, and which uses the same mechanisms of cellular motility that we find in free-living single celled organisms.
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Excitability. This was the toughest of the three to explain, because I wasn't talking to an audience of biophysicists. Our neurons (actually, all of our cells; even egg cells have interesting electrical properties) maintain an electrical potential, a voltage, across their membranes that you can measure with very tiny electrodes. This voltage undergoes short, sharp transient changes that produce action potentials, waves of current that move down the length of the cell. How do they do that? Where did this amazing electrical trick come from?
The explanation lies in a common problem. Our cells have membranes that are permeable to water, and they also must contain a collection of proteins that are not present in the external environment. The presence of these functional solutes inside the cell should create an osmotic gradient, so that water would flow in constantly, trying to dilute the interior to be iso-osmotic (the same concentration) as the outside. Some cells have different ways to cope: one way is to build cell walls that retain the concentration in the interior with pressure; another is to have specialized organelles to constantly pump out water. Our cells use a clever and rather lazy scheme: they compensate for the high internal concentration of essential proteins by creating a high external concentration of some other substance, which is impermeant to the cell membrane. Water has the same concentration inside and outside, but there are different distributions of solutes inside and outside.
What we use to generate these differential distributions are ionic salts, charged molecules. Positively charged sodium ions are high in concentration outside, while positively charged potassium ions and negatively (on average) charged proteins are high in concentration on the inside. Because these are charged ions, their distribution also coincidentally sets up a voltage difference. I confess, I did show the audience the Goldman equation, which is a little scary, but I reassured them that they didn't have to calculate it — they just needed to understand that the arrangements of salts in cells and the extracellular space generates a voltage that is simply derived from the physical and chemical properties of the situation.
We use variations in these voltages to send electrical signals down the length of our nerves, but they initially evolved as a mechanism to cope with maintaining our salt balance. We're also used to thinking of these electrical abilities as being part of a complicated nervous apparatus, but initially, they found utility in single-celled organisms. As an example, I described the behavior of paramecia. The paramecium swims about by beating cilia, like little oars; the membrane of the paramecium maintains an electrical potential, and also contains selectively permeable ion channels that can be switched open or closed. When the organism bumps into an obstacle, the channels open, calcium rushes in as the potential changes, and the cilia all reverse the direction of their beating, making the paramecium tumble backwards. The electrical properties of your brain are also functionally useful to single-celled organisms.
I concluded this section by trying to reassure everyone that their brain is something more than just a collection of paramecia swimming about. Although the general properties of the membrane are the same, evolution has also refined and expanded the capabilities of the neuronal membrane: there are many different kinds of ion channels, which we can see by their homology to one another are also products of evolution, and each one is specialized in unique ways to add flexibility to the behavioral repertoire of the cell. The origins of the electrical properties are a byproduct of salt homeostasis, but once that little bit of function is available, selection can amplify and hone the response of the system to get some remarkably sophisticated results.
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Synaptic signaling. Shuttling electrical signals across the membrane of a cell is one thing, but a nervous system is another: that requires that multiple cells send signals to one another. A wave of current flowing through a membrane in one cell needs to be transmitted to an adjacent cell, and the way we do that is through specialized connections called synapses. A chemical synapse is a specialized junction between two cells: on one side, the presynaptic side, a change in membrane voltage triggers the release of chemicals into the extracellular space; on the recieving side, the post-synaptic side, there are localized collections of receptors for that chemical signal, and when they bind the chemical (called a neurotransmitter), they cause changes in the membrane voltage on their side.
Once again, the cell simply reuses machinery that evolved for other purposes to carry out these functions. Cells use a secretory apparatus all over the place; we package up hormones or enzymes or other chemicals into small balloons of membrane called vesicles, and we can export them to the outside of the cell by simply fusing the vesicle with the cell membrane. Lots our cells do this, not just neurons, and it's also a common function in single celled organisms. Brewer's yeast, for instance, contain significant pieces of the membrane-associated signaling complex, or MASC, althogh they of course don't make true synapses, which requires two cells working together in a complementary fashion.
I described the situation in Trichoplax, an extremely simple multicellular organism which only has four cell types. The Trichoplax genome has been sequenced, and found to contain a surprising number of the proteins used in synaptic signaling…but it doesn't have a brain or any kind of nervous system, and none of its four cell types are neurons. What a mindless slug like Trichoplax uses these proteins for is secretion: it makes digestive enzymes, not neurotransmitters, and sprays them out onto the substrate to dissolve its food. Again, in more derived organisms with nervous systems, they have simply coopted this machinery to use in signaling between neurons.
As usual, I had to make sure that nobody came away from this thinking their brain was a conglomeration of Trichoplax squirting digestive enzymes around. Yeast, choanoflagellates, and sponges have very primitive precursors to the synapse; we can look at the evolutionary history of the structure and see extensive refinement and elaboration. The modern vertebrate synapse is built from over 1500 different proteins — it's grown and grown and grown from its simpler beginnings.
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Pathfinding. How do we make circuits of neurons? I've just explained how we can conduct electrical signals down single cells, and how pairs of cells can communicate with each other, but we also need to be able to connect up neurons in reliable and useful ways, making complex patterned arrangements of cells in the brain. We actually know a fair amount about how neurons in the developing nervous system do that.
Young nerve cells form a structure called the growth cone, an amoeboid process that contains growing pieces of the cell skeleton (fibers made of proteins like tubulin and actin), enzymes that act as motor proteins, cytoplasm, and membrane. These structures move: veils of membrane called lamellopodia flutter about, antennae-like rods called filopodia extend and probe the environment, and the whole bloblike mass expands in particular directions by the bulk flow of cytoplasm. The cell body stays in place, usually, and it sends out this little engine of movement that trundles away, leaving an axon behind it.
"Amoeboid" is the magic word. The growth cone uses the same cellular machinery single-celled organisms use for movement on a substrate. Once again, exaptation strikes, and the processes that amoebae use to move and find microorganismal prey are the same ones that the cells in your brain used to lay down pathways of circuitry in your brain.
Furthermore, there is no grand blueprint of the brain anywhere in the system. Growing neurons are best thought of as simple cellular automata which contain a fairly simple set of rules that lead them to follow entirely local cues to a final destination. I described some of the work that David Bentley did years ago (and also some of my old grasshopper work) that showed that not only can the cues be identified in the environment, but that experimental ablation of those intermediate targets can produce cells that are very confused and make erroneous navigational decisions.
We also contain a great many possible signals: long- and short-range cues, signals that attract or repel, and also signals that can change gene expression inside the neuron and change its behavior in even more complicated ways. It's still at its core an elaboration of behaviors found in protists and even bacteria; we are looking at amazingly powerful emergent behaviors that arise from simple mechanisms.
And that was the story. Properties of the nervous system that are key to its function and that many of us naively regard as unique to neurons are actually expanded, elaborated, specialized versions of properties that are also present in organisms that lack brains, nervous systems, or even neurons…and that aren't even multicellular. This is precisely what we'd expect from evolutionary origins, that everything would have its source in simpler precursors. Furthermore, it's a mistake to try and shoehorn those precursors into necessarily filling the same functions as their descendants today. Cooption is the rule. Even the brains of which we are so proud are byblows of more fundamental functions, like homeostasis, feeding, and locomotion.
Life Science
Comments
Posted by: Lee Picton | December 5, 2009 3:31 PM
PZ, thanks so much. That was an elegant summary - to think that I am being taught college level biology without any course fees just blows me away.
Posted by: Glen Davidson | December 5, 2009 3:31 PM
Good explanations.
I suppose I'm being picky--but then this is what some IDiots/creationists might being up--but I think it's not clear that nothing evolved for a purpose. The question depends upon what is meant by "purpose," of course, yet sexual selection would seem to open the door to evolution for a "purpose."
Human evolution in particular might be argued to have involved purpose in sexual selection. Enlarged breasts when not lactating, and the large (by comparison with other primates) human penis could very well have been selected "on purpose."
Doesn't detract from the fine explanations given. But I know that I tend to guard against this exception to "no purpose" in scientific evolution when countering the IDiots, because it's the kind of basically meaningless exception that they'd love to pounce on--fortunately, most aren't bright enough to do so, however there are exceptions.
Glen D
http://tinyurl.com/mxaa3p
Posted by: 'Tis Himself, Quel Dommage
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December 5, 2009 3:36 PM
Take that, all you folks who claim Pharyngula never has science.
Thanks, PZ, for explanations so simple that even I can understand them.
Posted by: PZ Myers
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December 5, 2009 3:41 PM
Even your examples aren't instances of purpose. There is no intent, no prior justification...those are found utilities.
The word "purpose" is entirely inappropriate. Richard Dawkins has tried to deal with it by inventing a new term for the kind of purpose you're talking about, but I think we're better served by trying to cut that misconception off at the knees. No, ankles. No...we need to blow it off its feet and scour the footprints from the floorboards.
Posted by: Citizen of the Cosmos
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December 5, 2009 3:50 PM
That was incredibly interesting. Thank you!
Posted by: Glen Davidson
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December 5, 2009 3:52 PM
Obviously sexual selection involves a lot of "non-purpose," getting hot because various shapes, sizes presumably, and configurations set off certain neurons in the brain, and "purpose" tends to go by the wayside.
Not entirely, though, and especially not when females are considering long-term mates. She might not be especially attracted to a short guy in the first place, but she also thinks, 'I don't want my sons to be short.' Males seem not so picky, or as oriented toward how their future progeny will turn out, but I don't think that they're entirely oblivious to such matters, especially when getting married.
No, I wouldn't retract the idea that sexual selection among humans is done with purpose being involved.
However, I've now said my piece, and if we disagree, we disagree, and I believe that I have no more to add.
Glen D
http://tinyurl.com/mxaa3p
Posted by: Anthony Popple | December 5, 2009 4:11 PM
It was a good lecture for someone like me.
It helped that I had just finished the chapter in Dawkin's latest book regarding embryology. He talks about "local units" following local rules. I though PZ’s discussion of “path-finding” meshed very well with this idea.
Posted by: heather | December 5, 2009 4:15 PM
The way I understand it, those sexual signals (large breasts, large penis) did not evolve to provide a signal, but evolved as a result of selection by potential mates on those particular traits. We can now use them as criteria on which to base our selections, but they did not come about in order to provide us with that criteria.
Posted by: Menyambal | December 5, 2009 4:17 PM
My brain is a byblow of homeostasis and feeding? My wife has been saying that for years, although she doesn't make it sound so scientific.
Seriously, PZ, a great article. Very interesting, clear and educational. Thank you very much.
I have a vaguely-related biological/nerve question. What is the origin of the odd circumstance that the left side of the brain controls the right side of the body (and vice versa), or is that just a myth?
Posted by: Sven DiMilo | December 5, 2009 4:18 PM
Cool talk, nicely explained!
Next time you need to illustrate the Goldman equation, (or, rather, the effects of ion concentration gradients and membrane permeablity on transmembrane electrical potential), try this fantastic visual tool:
http://www.nernstgoldman.physiology.arizona.edu/
Yep, and, as you allude, also for neuroendocrine, endocrine, and paracrine chemical communication among cells. And also, as an origin and/or elaboration of the receiving end, sensory processes of chemoreception. The common evolutionary root of all such chemical sensing and signalling systems is beautifully easy to imagine. (Especially given the commonality of signal transduction systems--e.g., G-proteins and second messenger systems--on the reciving end of all of them.)
Do we know anything about chemosensation or paracrine function in Trichoplax?
And about the neuron growth cones, it's also worth mentioning the other amoeboid cells in our bodies--macrophages that crawl around in loose connective tissue, patrol the lungs, and move in and out of blood vessels under their own semi-independent power are pretty cool cells to think about.
Posted by: Sowmya Rao | December 5, 2009 4:27 PM
Thank you for such a lovely article. It clarified quite a few things that I remember from my high school biology.
Posted by: Knockgoats | December 5, 2009 4:31 PM
Excellent stuff - thanks very much. Incidentally, the bit about there being no blueprint for the brain links to Buller's critique of the EP claim that our minds consist of hundreds or thousands of specialist modules selected in the course of our evolution for specific tasks. He notes that the growing brain vastly overproduces connections between neurons, then many of them die off as a result of disuse.
Posted by: Sven DiMilo | December 5, 2009 4:34 PM
I should probably read Buller, but it's not immediately clear to me why an overproduction/winnowing process couldn't result in "specialist modules selected in the course of our evolution for specific tasks."
Posted by: Thomas Galvin | December 5, 2009 4:40 PM
As a layman, I think this is one of the most important concepts in biology today. Our minds are built to detect agency, to see intent and to anthropomorphize, and that kind of "breaks" the way we think about evolution.
A couple of days ago, a girl asked me why giraffes have such long necks, and the quick, obvious answer is "so they can eat the leaves that are higher up on the trees," but this isn't really true. The truth is that one proto-giraffe was born, randomly, with a longer neck, and this happened to provide the benefit of being able to reach food on higher branches. The result is the same, but the agency is removed.
This confusion is a big part of why people see design where there is none.
Posted by: quasi13
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December 5, 2009 4:59 PM
"Richard Dawkins has tried to deal with it by inventing a new term for the kind of purpose you're talking about..."
Are you referring to "archeo purpose"?
Posted by: bettyjoebob | December 5, 2009 5:00 PM
I feel that I owe you something. Here are some choices unless you can come up with something better:
- A footbath
- Some burnt meat
- A box, 2 cubits by three cubits, lined within and without in gold with a seat above the box...
thanx
Posted by: Timothy (TRiG) | December 5, 2009 5:22 PM
That was fascinating. Thanks.
TRiG.
Posted by: Peter Ashby | December 5, 2009 5:24 PM
@Glen Davidson
I think the thing to remember is that we humans tend to privilege things we consciously think about as being special to us. However other animals, many of them not even mammalian or even avian do exactly those sorts of calculations, only instinctively. Thus that we can think about them adds no particular utility apart from frustrating biological evolution for other purposes which is not necessarily a good thing in terms of species preservation so it is not clear that they are adaptive.
Posted by: Sachi Wilson | December 5, 2009 5:29 PM
"I concluded this section by trying to reassure everyone that their brain is something more than just a collection of paramecia swimming about."
Are you sure? It could explain the thought processes of the ID proponents.
Posted by: Peter Ashby | December 5, 2009 5:46 PM
In addition, many of the reasons we give for such decisions can be shown to be post hoc rationalisations of what the psychologists can show us are unconscious processes. You may think you are attracted to her because you like her hair when in fact you have sniffed each others' HLA genes and have discovered you are neither too closely related nor too unrelated.
So the function of the post hoc rationalisations wrt the sort of things that help species preservation is almost entirely obscure.
Posted by: North of 49 | December 5, 2009 5:54 PM
Sheer poetry. This whole post is exactly the kind of example I often find myself needing, so thank you, PZ, in fact merci beaucoup.
One of my hobbies is imagining how New Agers and alt-med mavens will react to -- and probably abuse -- information just like this.
For the New Agers, at least, I predict that in spite of the lucidity and simplicity of your explanation it will still be twisted, morphed, mutilated and cherry-picked to "prove" that Chopra was right, consciousness is everywhere, see, even something as simple as a bacterium can "think". Science said so! (If you squint hard and plug both ears.)
But... Nothing evolved for a purpose is a perfect counter to all that. If there is purpose then there should be evidence of it. Where is it?
What's that? Nope, evolution doesn't work that way. Best two out of three? Oh, that. But now you're proposing a supernatural explanation for a phenomenon that has a perfectly natural one. Best four out of seven?
(Rubs hands in anticipation.)
Posted by: amphiox | December 5, 2009 5:55 PM
With regards to purpose and sexual selection, I think that although there may be purpose in the selecting, there is no purpose in the adaption. The adaption results because of the selection, it does not arise with a purpose of fulfilling the selective need.
The word purpose implies intent and forethought. To say that big breasts arose for the purpose of attracting men, or tallness arose for the purpose of attracting women, supposes the existence of an unfulfilled need, the recognition in some form of the need that is to be fulfilled, and some mechanism by which adaption can be deliberately targeted towards the pre-existing need.
But that isn't what happens in sexual selection or any other type of selection. The real process is actually the reverse, and the illusion of purpose is inferred after the fact, and erroneously so.
Posted by: Dr. I. Needtob Athe | December 5, 2009 5:57 PM
"Our cells use a clever and rather lazy scheme..."
Are you sure "clever" is the word you want to use here? It doesn't fit very well with your "nothing evolved for a purpose" theme.
Posted by: Anonymous | December 5, 2009 6:05 PM
Too bad you can't prove the evolution of the immune system though. Behe told me that science can't explain it.
Posted by: PZ Myers
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December 5, 2009 6:10 PM
There's actually an interesting literature out there about how immunoglobulins may actually be coopted cell recognition proteins that first evolved in specifying neurons. Or at least, some of the protein motifs were snatched from ns proteins.
Posted by: efrique | December 5, 2009 6:18 PM
Very clear and extra-nifty.
(I can't read this without thinking that Darwin would have been so excited to learn some of these details.)
Posted by: Janet Holmes | December 5, 2009 6:20 PM
Thanks so much for that PZ, it's been a very long time since my science degree and things are so much better understood now than they were then. It's nice to catch up a little.
Posted by: NoFear
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December 5, 2009 6:23 PM
Excellent post, PZ, and thanks!
The discussion here shows yet again how it is important to let go of our egos to understaqnd the universe. Once we let go of the idea that we were the center of the solar system and the universe, cosmology suddenly started to make sense. Once we let go of the idea of "purpose", which is a purely human idea as far as we can tell (maybe some other animals have a sense of purpose, but we have no way of knowing that), evolution starts to make sense.
@ word slinger # 25
Nothing was purposely coopted. Through a mutation, or other change in genetics and/or the phenotype thus generated, a part started performing some new function. This new function proved benefical to that organism's, and hence its genes, reproduction rate so that that gene and it's associated phenotype became more common in the gene pool.
It is difficult not to use phrases like "co-opted", but using such phrases should not be problematic as long as one understands the context in which the word is used. You need lessons in biological and evolutionary context. Until you understand that, you will forever be lost when trying to understand and article of the sort posted above by PZ.
And soapbox derby cars do not imperfectly self-replicate so your analogy fails. We are talking about imperfectly self-replicating entities. Analogies that refer to entities that do not do that are fallacious.
Posted by: amphiox | December 5, 2009 6:27 PM
"Co-option is not random, accidental or unguided.
It requires intent, purpose and intelligence."
In this context, it does not.
You are twisting the meaning of the words "co-option", "intent", "purpose" and "intelligence".
If this is because you have failed to understand them properly, I suggest you re-read this post carefully, perhaps with the supervision and advice of a more knowledgable friend, and then go educate yourself before attempting to comment again on a process you clearly do not comprehend.
If, on the other hand, you do understand, but continue regardless to pursue this argument, then know that you are violating the 9th Commandment.
Posted by: NoFear
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December 5, 2009 6:32 PM
@ word slinger #27
You are confusing the specific word used with the idea it is trying to represent. Try to focus less on the specific word used and more on the overall idea being presented.
But of course you want to focus on the specific word because that is the only way you can try to make your flawed case for some form if ID.
ID is bullshit. Get over it. You are evloved, though perhaps not as much as others posting here.
Posted by: Marcus | December 5, 2009 6:41 PM
@27
Fail.
Intent is not required. E.g.
A gust of wind snatched the umbrella from his grasp.
Posted by: David Marjanović, OM | December 5, 2009 6:44 PM
...those with too short necks have already died out.
(In the savanna, that is. Not in the rainforest, which imposes another definition of "too short".)
Posted by: Insightful Ape | December 5, 2009 7:12 PM
Hey stupid word slinging troll,
Why don't jackasses like you ever come up with a publications, or in anyway adding to existing knowledge? Why can't do any better than games of words like "snatched" needing "intent", as if words that were invented to describe human affairs should have the exact same meaning why applied to cells and molecules?
Thanks a lot for the article PZ, but we need better troll removers. Now if we could "snatch" a web hosting tool and "co-opt" it for this purpose it would be great.
Posted by: NoFear
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December 5, 2009 7:17 PM
Sorry, word linger, I thought you were serious in your previous posts. Apparently you were just being a poe. Or maybe you were being serious and your 11th commandment is the one you follow most.
Either way, I am sorry for 1) your lack of thinking ability or 2) my taking your earlier ludicrous statements seriously.
Posted by: BenW
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December 5, 2009 7:17 PM
If Alabama beats Tim Tebow can we say that is proof that there is no God?
Posted by: Malcolm | December 5, 2009 7:17 PM
There is no point arguing with wordslinger. It isn't here to learn anything. It is here to preach.
Posted by: Jadehawk, OM
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December 5, 2009 7:30 PM
thanks PZ, that was a great little lecture :-)
Posted by: Jim Harrison | December 5, 2009 7:49 PM
Point of information: Have you got any sense of how well this lecture went over. I found it extremely clear and informative; but, if I had to guess, I'd expect that it would sail far over most people's heads.
Posted by: NoFear
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December 5, 2009 7:50 PM
Oh, so word slinger is not a poe? Good to know.
Posted by: Anon | December 5, 2009 8:02 PM
I must say, it is comforting to hear that biologists have to suffer through the same assumptions of "intention" and "purpose" that I do. The trick is, as a behaviorist, my job is to explain that the things that we do, not just the things that we are, are the result of building on past success, discarding of past failure, and not some future "purpose". Even people who are perfectly content with natural selection can take offense at the notion that our behavior is also selected for by our environments.
Just yesterday I spent an enjoyable half an hour turning a student's world upside down, explaining that taking a walk with the intention of mailing a letter was actually controlled by past events, not by the future event of mailing the letter. I'll spare you the details here, as it would rival the length of PZ's post here... come to think of it, I rather wish I had read PZ's post first, because it really has some striking parallels.
Interesting, that Dan Dennett's new talk on "the evolution of reasons" has him concluding that memes allow us to engage in purposeful, future-driven behavior... while Sue Blackmore looks at precisely the same evidence to conclude that we do not.
Thanks, PZ, for a pithy, elegant, and very worthwhile explanation. This is one for re-reading a number of times...
Posted by: Ray Moscow | December 5, 2009 8:26 PM
Thanks, PZ. Reading your blog is an education in itself.
Posted by: ConcernedJoe | December 5, 2009 8:38 PM
Very nice PZ - thanks
Posted by: Insightful Ape
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December 5, 2009 8:46 PM
I almost feel sorry for how stupid our newest troll is.
(Unless he/she is a Poe of course).
How can anyone look at a scientific presentation, totally ignore the substance, and just play a game of words to get it to mean the opposite of what it says?
Sadly, even the more "serious" creationists like Behe have been doing no better. Not publishing anything new; just taking the words of legitimate scientists out of context and spinning them to fit their agenda. (And singing la-la-la when called out on their dishonesty).
Posted by: My Lord! | December 5, 2009 8:48 PM
Thanks for the talk PZ. I thought that your explaination for why some species of flies have such quick reaction times (other then their size) was very interesting. You would think that mutations to increase the "pipe" size of the axion or to create an axion that was more targeted to immediate flight (as in running away, not actual flight, as discussed with the fish example) would in many conscievable cases be selected for. Why do humans then have such slow reaction times (other than distance from brain to synapse)? I want to be faster.
Posted by: DaveH_of_Lundun | December 5, 2009 8:51 PM
@45,
The immune system itself isn't a living organism, so why exactly do you object to the metaphor?
Posted by: Butch Pansy | December 5, 2009 8:59 PM
Words linger long after their sense has evolved. We are stardust but there are still stars.
Posted by: kamaka | December 5, 2009 9:14 PM
Word Slinger,
The evolutionists will never, ever get it till they understand what the Jesus protein is all about.
Posted by: NoFear
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December 5, 2009 9:47 PM
The Jesus protein? LMAO! That must be the protein that destroys neurons.
Posted by: No BS | December 5, 2009 10:20 PM
Hey, thanks PZ, good lecture.
Wordslinger, autofellatio, keep trying, you'll reach it eventually.
Posted by: kiwi Dave | December 5, 2009 10:20 PM
That was utterly fascinating and fairly clear, even to this complete non-scientist.
Once again, I regret having gone the arts road in education.
And as a side issue, how could anyone after reading this suggest that somehow materialistic science reduces the wonder of the universe?
Posted by: F
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December 5, 2009 10:22 PM
Whoa! I was thinking about spandrels not an hour or two before I saw this. Spoooooky.
Now I'll just go read it...
Posted by: Paula Helm Murray | December 5, 2009 10:27 PM
Thanks for sharing that. I thought that you explained those parts of the dance of life elegantly. I'm an amateur biologist, but in the macro sense/natural history sense -- I know a lot about the life habits of a lot of vertebrates, am a bit fuzzier but know about mollusks and know which insects are what but don't want to know more).
Posted by: Dax | December 5, 2009 10:30 PM
Happy Witch Bull Day
525 yrs ago today in 1484 Innocent 8th while chewing on a cracker and hiding a choirboy under his dress decided he REALLY didn't like black cats and women. Not much has changed.
Posted by: amphiox | December 5, 2009 10:30 PM
Just the 11th and 12th, Word Slinger, eh? So you don't follow the 4th, 5th, or 6th, then?
Good to know.
Where do you live, by the way? I shall add it to the places I will tell my children to avoid.
Posted by: Bubs | December 5, 2009 10:39 PM
OK, this is just too much. The anti-adaptationist school has wildly overstated their case. You speak of the ubiquity of co-option and exaptation as the Rule with authority that isn't warranted. This is still a major question in evolutionary biology and you speak as if it's solved. You should also note that the sense in which you use the idea of exaptation is almost trivial--yes, essentially everything comes from something that came before it, so what? The interesting questions about this are things like (a) does this pose a major problem to the view of evolution as an optimizing force and (b) what's the real picture of constraint in evolution?
Posted by: amphiox | December 5, 2009 10:44 PM
"Why do humans then have such slow reaction times (other than distance from brain to synapse)?"
Are humans really all that slow? We don't have the specialized superfast reactions of some animals, but my guess is that our reaction times would slot comfortably into the average among non-specialist species of comparable size and metabolism.
(I don't know if the numbers are exact, or even if this is just an urban myth, but I recall hearing somewhere that a well-trained human, like a martial artist or a special forces commando, or even an experienced snake researcher, actually has reflexes and reactions up to 8 times faster than the average snake can strike)
The same can be said of our senses, which are not poor compared to those of other animals, but actually average. (Which is to say that while we are no match for the super-specialists in the individual senses of their specialization, when comparing individual species to each other, rather than humans to the entire rest of the animal kingdom, and looking at all the senses together as a whole, we hold our own quite nicely)
Overall, when it comes to CNS functions, the selection pressures acting on our lineage seems to have favored the route of developing generalized abilities that can be flexibly applied to a wide variety of challenges, as opposed to specializing in some particular subset of superskills.
Posted by: amphiox | December 5, 2009 10:58 PM
#61:
I'm not sure I understand your objection here. While I am familiar with the neutral vs adaptionist paradigms, I fail to see how co-option and exaption can be said to apply to one over the other, or be constituted as evidence in favor of one and against the other. As far as I am concerned, an exaption IS an adaption the moment selective pressure starts to apply to it in its "new" role, regardless of whether it originated due to selection applied to some other role, and even here it is STILL an adaption, for the older role.
For example cell signaling pathways developed as adaptions, not neutral traits (maybe they first arose as neutral traits, but the moment they became useful to the cells, they ceased to be neutral and became adaptions), and when these same pathways were exapted for synapses, they continued to be adaptions, and not neutral traits.
Posted by: Samantha
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December 5, 2009 11:18 PM
Soooo... basically, purpose was created by the evolution, not evolution created by the purpose? That makes sense to me.
Word Slinger @ #45
In a description of an inanimate object as being a living person or animal the "intent" refers to the entity o which the personification refers,
This might have been arguable a few hundred years ago (maybe) but it is not today. The colloquial and contextual meaning of the word snatched has broadened beyond the original usage, as most words have. I think you'd have a tough time convincing any literature professor that a simple sentence like the example shows true personification. Snatched does not imply intent unless combined with an adverb that adds said intent. You might think that you're clever arguing language and rhetoric on a science blog but there are some English students that lurk, and may I speak for us all when I say that you might as well just stop now because you clearly don't know much if anything about the subject.
Posted by: CB | December 5, 2009 11:54 PM
So cool! I'm recently into neuroscience and have a thing for evolution, but I never gave much thought to how neurons' special properties are derived - until now. Wish you were my professor :D
Posted by: Owlmirror | December 6, 2009 12:08 AM
Huh.
My evolved amoeboid paramecium-like neural-net has just gone and tossed out a pattern match on "Word Slinger" as being stylistically similar to ... Charlie Wagner.
Additional evidence, such as an IP address in Hawai'i, is not accessible to me, but I wonder what would happen if I started Googling the phrases that "Word Slinger" uses?
Hm, hm, hm.
Could just be a false positive. Could just be a coincidence.
But maybe my intelligence is seeing design.
Posted by: snooty pedant | December 6, 2009 12:12 AM
"Nothing evolved for a purpose". Okay, I'll bite: what is the purpose for which "nothing" evolved? The editor in me is trying to find a simple and unambiguous way to say what you mean: That nothing which evolved, evolved for a purpose. "Evolution has no purpose"?
While on the subject... During conversations with intelligent non-biologists I have noted that they misinterpret my meaning if I refer to evolution as a "process". This is because "process" has overtones of purpose (as in "the manufacturing process"). I find that I can more easily get them to understand what evolution is if I refer to it as a "consequence" (of selection on a pool of variants).
Posted by: Colin Meier | December 6, 2009 12:31 AM
As a fan of in-silico CA, I'm interested to know if anyone's simulated this digitally...?
Apart from that, I think cytology and the nervous system are the most interesting bits of biology (apart from viruses), so thanks for this great article, PZ.
Posted by: Ben Breuer | December 6, 2009 12:47 AM
Thanks for posting your notes and summarizing your lecture! While my neuroscience chops have gotten a bit rusty over the years, I remembered enough--gratifying, that.
On exaptation/adaptation: I don't recall Gould's original definition. But is the exaptive (exaptative?) feature actually lost when the adaptive feature comes to bear? Then again, I suppose a reverse evolutionary pathway from nerve cells towards locomotors would be unlikely.
Posted by: My Lord! | December 6, 2009 1:37 AM
@ 56 - Amphiox
Yeah, but, and this is just me talking, I assume in the several million year evolution of the Homo s. line from our LCA of Chimps that there must have been mutation to axion size. Why would such a mutation, assuming that mere axion size controls for faster reactions (as I understood from the lecture (again, it was to a general audience, so I assume that PZ glossed over a lot of detail)) not be selected for as it would seem to benefit us. Maybe the answer is it would not benefit us as we generally are not trying to catch flies in chopsticks a la Daniel-son (wahhhh). However, it would seem to give an advantage to one group of Homo e., Homo s. or other relative, when fighting a neighboring group, fighting for mates, timing and throwing spears, rocks, etc., and playing baseball.
Posted by: scott | December 6, 2009 1:56 AM
PZ -- are you citing some unpublished data on the role of synaptic signaling proteins in Trichoplax or liberally hypothesizing about their roles in very matter-of-fact terms? To my knowledge, your claim that they function in secreting digestive enzymes are not substantiated in the literature... In fact, I don't know anyone who has documented how they actually feed.
Please correct me if I'm wrong. I'd be astonished to have missed such an interesting body of literature.
Thanks.
Posted by: Peter Ashby | December 6, 2009 6:01 AM
@MyLord!
Firstly the word is axon, there is no 'i'. Secondly wrt us mammals we developed a way to have fast axon transmission time without having huge axons*. It's myelination, where specialised glia cells called Schwann Cells wrap the axons in layers and layers (in x-section they look like onions) of insulating lipid with only small gaps between Schwann cells where the axon is open. The axon only has voltage gated ion channels in the gaps and they spaced just so far apart that the depolarisation from the firing of the previous gap is just enough to set the next one off. A situation so clearly tuned by selection, it is elegantly beautiful. So the action potential travels by jumping down the axon open node to open node. I won't give you the maths, but part of the beauty requires an appreciation of esoteric concepts like the Time Constant.
*the biggest unmyelinated axons are found in squid. It runs from the brain to the escape muscles and in an average sized squid its a millimetre across. Neurophysiology began by investigating axon potentials in these.
If we had not developed myelinated axons then our brains would have to huge for us not to be absolute sluggards and the nerves in your limbs would rival your muscles for size. Schwann cells are the ones that go in MS, when they are not there doing their insulation thing the action potentials can't travel.
Posted by: Stagyar zil Doggo | December 6, 2009 6:07 AM
Thanks for the cogent and accessible talk. The more interesting bits of course would come in the following lecture(s). How do these neural processes decide where (and with whom) to synapse? And within what narrow parameters must the rules specifying these neuronal cellular automata be constrained so as to lead to the emergent phenomenon of a thinking mind?
Off topic:
I've been searching online for an introductory (video) course on neuroscience, so far without success. Could anyone here point me to one?
Posted by: Peter Ashby | December 6, 2009 6:10 AM
Sorry, I should also have said that the speed of transmission down an axon is proportional to its x-sectional area. However the dial gets reset for myelinated axons such that you can get high speed off small x-section myelinated axons. All that myelin wrapping axons is why our nerves are bright white in colour.
We do have some unmyelinated axons, mainly on the sensory side. Pain is transmitted via unmyelinated axons while senses like touch are not. Which may be why there is that horrible delay when you know you have hurt yourself and you wait for the inevitable wave of pain to arrive.
Posted by: Steve in Dublin | December 6, 2009 6:17 AM
And:
A little bit derivative, PZ, but the quality of the original source material you are citing is impeccable. And hey, I'm learnin' freakin' *biology* at the same time!
Posted by: ConcernedJoe | December 6, 2009 6:47 AM
Scott I am not qualified to argue a case and I admit it; I hope others qualified will address your concern objectively but I give my reading.
I think it is agreed in the official literature that the fiber syncytium in Trichoplax act consistent with the essence of what PZ was trying to convey. So in my rusty mind I thought I agreed with PZ's point. But I could be showing my ignorance.
I guess the hyperbole of "squirting digestive juices around" is not exact sciencey talk but he was making a point to laypeople in a limited presentation (so poetic license he's allowed I figured).
Again - I hope qualified people (that ain't me) can address your concern (I assume your concern was either the essence of what PZ said has no basis at all or is patently a stretch of the facts that is a foul). I'm very interested to see if PZ went Creationist on us in this presentation :-).
Posted by: mo | December 6, 2009 8:08 AM
Where are the two schemes of the evolution of the nervous system - pylogenetic tree and addition of gene groups - from?
I guess it was a Nature Review, and I would love to read it. Please give me a Pubmed link.
Posted by: R. Schauer
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December 6, 2009 8:22 AM
I'm sorry, PZ...but this well written explaination of exaptation doesn't nearly reproduce the charming elegance of your lecture from the other night...nor does it convey your amenable wit and mirth or skillful delivery methodology.
I must say, PZ live is really something to behold...kinda like a U2 concert.
Posted by: ice9 | December 6, 2009 9:56 AM
PZ, please go back to atheist rabble-rousing and pwning denialists and creationists. Your reputation as a single mexican pig is suffering and soon Orly Taitz will demand proof that you are not actually several people.
Also please stop deleting the trolls before the latecomers get a chance to read them. I know nothing of science but you attract first-class knuckleheads. Plus it screws up the post numbers.
ice9
Posted by: David Marjanović, OM | December 6, 2009 10:53 AM
There I was going to comment on how Word Slinger was too stupid to understand fairly obvious metaphors (compare: "the atom wants to have 8 valence electrons", which just means that's the energetically most stable number), and now he's gone! I guess comment 60 was on to something. :-)
I don't know if the number is correct, but snakes are pretty slow, slower than humans.
(I don't know if this depends on the snake's body temperature and thus on the weather, however.)
Not us mammals. Us vertebrates, and several other clades like the crustaceans or some subset thereof.
Posted by: scott | December 6, 2009 10:55 AM
@ ConcernedJoe
PZ's comments about Trichoplax are spoken with a degree of certainty that suggests he's been to a conference and seen something that isn't yet published, or otherwise knows about something in the pipes --- so I don't want to call it science fiction.
Nevertheless, to the best of my knowledge, it is fiction. This is relevant to my research area and I watch it closely -- nobody has demonstrated what ANY gene does it Trichoplax, yet. Much less have they documented how conserved synaptic proteins interact and function to regulate feeding. That would be MAJOR.
I'd argue that this is sketchy "science reporting" if you will.
Posted by: Sven DiMilo | December 6, 2009 10:56 AM
You're probably correct about the literature. But it's not a very liberal hypothesis.
We know they eat, we know they can eat algae, we know they absorb nutrients through the ventral surface. They must be secreting enzymes; enzymes are proteins and must be secreted by exocytosis, as in synapses. It's the machinery of inducible exocytosis that accounts for the gene homologies, I'll bet. Or liberally hypothesize, rather.
Posted by: Scott | December 6, 2009 11:03 AM
@ Sven DiMilo,
I don't care how plausible it is. It isn't known. Just-so-stories aren't science. We must test our claims...
Posted by: Pierce R. Butler | December 6, 2009 11:05 AM
Glen Davidson @ # 2: ... the large (by comparison with other primates) human penis could very well have been selected "on purpose."
heather @ # 8: ... large penis... evolved as a result of selection by potential mates ...
Alas, the idea that Groo-la chose Thag for a mate because he was well-hung doesn't always match up with ethological data.
I can't find anything on my shelves that deals with this, but I've read numerous accounts that large penises correlate very strongly with the observed frequency of coercion in sex within various species. In short: large-dicked rapists impregnated more victims than the less-endowed.
Another claim is that in gang-bang situations (perhaps more frequent when females had a more pronounced cycle of estrus), larger penises were more effective at delivering sperm to the cervix, and at displacing their rivals' semen.
Other observations are more ambiguous:
Posted by: PZ Myers
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December 6, 2009 11:10 AM
That's an entirely fair comment: Trichoplax is kind of a mystery. My statement was reasonable speculation, nothing more.
It isn't at all far-fetched to say that these proteins are used for secretion. That's what they do! It's just also possible that Trichoplax also uses them for, for instance, hormone release.
Posted by: scott | December 6, 2009 11:16 AM
Fair enough, PZ.
I'd still argue that their ancestral roles weren't necessarily secretion though. Isn't that the whole point of exaptation?
A related function could even have been membrane cycling ... if there is endo/pinocytosis on the basal surface, you have to put membrane back somehow.
Best,
Scott
Posted by: PZ Myers
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December 6, 2009 12:03 PM
Yes! Push it back fair enough, and yeah, the synaptic machinery would have been involved in something other than targeted secretion, and membrane cycling is definitely a likely candidate. It's exaptation all the way down.
Posted by: Sven DiMilo | December 6, 2009 12:11 PM
No argument there. Personally, in the (acknowledged) absence of direct evidence, though, plausibility is the next criterion. In this case, IMO, the hypothesis goes beyond plausibility to it's-gotta-be status. I look forward to somebody empirically elucidating the obvious.
Posted by: amphiox | December 6, 2009 1:34 PM
I would very much like to see how big the squid giant axon is in a Colossal Squid.
But, as others have already stated, the saltatory excitation allowed by myelination increases conduction velocity by orders of magnitude. The only unmyelinated fibers vertebrates have are very small and comparatively slow.
Interesting that nervous system convergent evolution did not produce myelin in cephalopods. The size issue must surely put constraints with regards to the total number of axons they can have and thus the number and diversity of the target muscle groups. You'd think that it would limit speed and dexterity. (Although your typical octopus is plenty dextrous, and squid are damn fast) Such is contingency, I suppose.
(So take that, Cthulu, thinking you're so superior with that oh-so-more-logically wired up retina of yours? Well, ha!)
I didn't know crustaceans had myelin though. That's cool. Is it the same as vertebrate myelin, or is it some other fatty substance?
Posted by: Sven DiMilo | December 6, 2009 1:52 PM
Me neither! via Teh Gooogle, lots of good info on invertebrate myelin here...annelids too! Looks like some fascinating similarities and differences.
Posted by: Sven DiMilo | December 6, 2009 2:00 PM
e.g., it's all phospholipid bilayer (cell membranes), but invertebrates seemingly have various patterns of multicellular concentric wraps instead of unicellular spiral wraps. And the nodes are not necessarily circumferential, as in vertebrate Nodes of Ranvier, but may be window-like fenestrations instead. Very cool indeed but almost certainly convergent.
Posted by: My Lord! | December 6, 2009 2:03 PM
@ 66 and 68.
Thanks! I obviously have a lot of reading to do. The talk about the nerve cell structure and coopting was very interesting and I have a ton of questions, all with seemingly logical answers, except for the fact that I now know 1/10 of 1/10 of 1/1000th of one percent of the knowledge and so the answer is simply based on something I don't know. I should audit a class at the U.
Posted by: Pareidolius | December 6, 2009 3:21 PM
I love these posts where the science makes every one of my monkey hair stand on end. You invoked a sense of awe in me regarding simple cells that I usually reserve for Hubble or Cassini photographs. I am much better informed today than yesterday. Thanks for posting this, your love of the subject is infectious and I think that makes you all the more effective as a teacher.
Posted by: amphiox | December 6, 2009 4:05 PM
"In this case, IMO, the hypothesis goes beyond plausibility to it's-gotta-be status"
Assuming that 1. Trichoplax is an animal, and 2. Common descent is true, and given 3. Trichoplax eats, and 4. Single celled eukaryotes ancestral to animals secrete digestive enzymes to extract nutrients from substrates, it would be almost inconceivable for this hypothesis not to be true.
If it were tested and actually falsified (ie Trichoplax doesn't use these systems to secrete digestive enzymes, but uses some other mechanism to do the same thing), it would be mind-blowing. It would suggest (at least to me)
A) Trichoplax is an independently evolved instance of multicellularity, separate from the other animals. (A remnant of a diploblastic radiation from the Vendian, independent of the primarily triploblastic lineages of all other animals??!!)
B) Trichoplax somehow lost the ability to secrete digestive enzymes inherited from its unicellular ancestors, and independently re-evolved another system for doing the same thing.
C) Trichoplax actually doesn't eat and we've been wrong all along about what the hell it is doing with algae.
D) Trichoplax is an alien hybrid.
E) Trichoplax is designed. (I can just imagine that: intelligent design is possible, but Trichoplax is the most complex thing it is capable of producing, and anything more complex requires Darwinian evolutionary processes!)
Posted by: ConcernedJoe | December 6, 2009 4:09 PM
Scott - Sven - PZ - Others --- interesting and fun to learn something.
And Scott you are right we should watch how we label examples.
Thanks again guys.
Posted by: scott | December 6, 2009 4:20 PM
@ amphiox
The unicellular ancestors of animals were thought to resemble modern choanoflagellates. At the very least, they were certainly bacterivorous filter feeders that engulf prey via phagocytosis. No digestive enzymes secreted/needed.
This same feeding is exhibited by modern sponges and was presumably in place in the last common multicellular ancestor of animals.
Both sponges and choanoflagellates have highly conserved synaptic proteins.
We don't know how Trichoplax eats. If it forms a "gut" between its basal epithelium and substrate, then this is a unique feeding method indeed. It is certainly plausible that they simply engulf bacterial/algal prey via phagocytosis.
There are no foregone conclusions about ancestral gene function. Even C. elegans uses many genes in very different ways than other animals -- many of which are derived functions in C. elegans.
I feel strongly that evolutionary biology has suffered from a lower standard of evidence than is possible and necessary.
No story is so "clean" that it is certainly true when talking about how things evolved 600-800 million years ago.
S
Posted by: ConcernedJoe | December 6, 2009 4:46 PM
Amphiox - for what it is worth (nothing) I lean your way.
But Scott has convinced me that it is not a Fact or universally accepted and thus until it is an official Fact it must be labeled as unproven hypotheses among competing hypotheses. And Scott is an expert and I do see his compelling technical counterpoints.
Scott is very right to insist on truth in labeling - our fervent beliefs (even exquisitely reasonable and logical ones) are not Facts - I am humbled.
Posted by: amphiox | December 6, 2009 4:58 PM
Of course you are correct, scott. I didn't mean to imply certainty, only a high likelihood.
Posted by: Jim Thomerson | December 6, 2009 6:11 PM
Gould and Virba coined exapation to replace preadaptation. One could understand preadaptation as implying purpose or design.
Posted by: David Marjanović, OM | December 6, 2009 6:38 PM
Molly nomination.
Vrba. No vowel in the first syllable, just the r.
Posted by: Sven DiMilo | December 6, 2009 8:30 PM
hmmmm. Scott's right, and now I want to know a whole bunch of more stuff: what exactly are the "synaptic genes" we're talking about, and how do their proteins function? How much overlap beween the molecular effectors of endo- and exocytosis?
Posted by: John Scanlon, FCD | December 7, 2009 12:05 AM
David Marjanović, OM #74 (post-troll-deletion numbering)
With snakes, it always depends on temperature (nonlinearly and with individual variation, but strongly). Also, evading strikes is always a matter of knowing what the snake can do before it starts doing it, so calling it a 'reflex' could mislead.
Pierce Butler #78, I remember chuckling when reading those lines you quoted, knowing that from the way they invoked moral and emotional issues, some readers would infer that Diamond and Jones were both small men.
Jim Thomerson #93, yes they did. But no evolutionary biologist had ever understood 'preadaptation' to imply design or purpose, so the substitution of terms seemed somewhat disingenuous at the time.
Posted by: JBabs073
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December 7, 2009 12:23 AM
Thanks for coming down to the U TC to lecture us. :)
It was excellent.
I was actually going to ask to see if you would post your PowerPoint online at the lecture, but I am pleased to see that not only did you post that, but a written summary as well! You have outdone yourself in awesomeness. :)
Keep up the good work, and I hope to see you back at the U soon! :)
Posted by: Colin Meier | December 7, 2009 3:22 AM
PZ, could I suggest when you delete a comment, you just mark it as 'comment deleted', so the numbering stays the same? I understand that might be too much of a hassle, obviously, especially with the volume of comments you get. (Also it might not be technically possible, I suppose, since it would amount to "editing" a contributed comment).
Posted by: Rewarp | December 7, 2009 3:38 AM
I would propose a nested commenting system as being more efficient. Everyone would be able to follow the discussion, and if the person turns out to be an unbearable troll, you could just single that specific thread out and remove the offending comments.
By the way, nice write-up. And I enjoyed reading the discussion initiated by scott as well. It is such a pleasure watching scientific minds arguing over scientific points.
Posted by: Jadehawk, OM
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December 7, 2009 3:41 AM
eww no. trolls that need deleting aren't that common, and the rest of them sparks the most interesting discussions. and cross-subthread discussions wouldn't be possible with nested threadsPosted by: Jud
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December 7, 2009 8:12 AM
Gosh PZ, I love when you "do science." :-)
Scott wrote: No story is so "clean" that it is certainly true when talking about how things evolved 600-800 million years ago.
Yah, "It makes perfect sense" could well be synonymous with "We don't yet know enough to see all the holes in this hypothesis."
Posted by: Peter Ashby | December 7, 2009 10:46 AM
@Jadehawk, OM
Have you never used a threaded usenet reader? I did for years and there is this feature called 'copy and paste' that makes it easy to do cross thread discussions. OR you put a link into the discussion in one thread that links the points in the next one.
I miss threading on the web, New Scientist manages it with its comment system and it works fine to me.
Posted by: David Marjanović, OM | December 7, 2009 11:03 AM
Threading would mean you basically need to read the entire page again and again to make sure you don't miss any new comments… I really like the strict chronological order.
So… you post the same comment twice on two subthreads? Or do you start a third? ~:-|
Posted by: Tulse | December 7, 2009 11:15 AM
Ditto. Coyne's blog uses threading, and it is a pain in the butt to see what the new comments are.
Posted by: AJ Milne OM
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December 7, 2009 11:19 AM
While on the subject of word coinage for stuff that just doesn't quite have words for it yet, I often find myself thinking we need some sorta new adjective that properly conveys the wild, muddled, mangled-yet-frequently-weirdly-incredibly-functional mess that is biology at the biochemical and genetic levels...
... as in: the picture I keep getting is of marvellously complicated yet consistently weirdly jury-rigged stuff. But call it 'intricate' because it's got all that detail and ins and outs and feedbacks and multistage stuff in it, and it sorta misses, really... because 'intricate' implies to me something more... streamlined, neat, even purposeful, which biology just doesn't do, really... And biology is full of these weird, awkward reuses and repurposings... and that's not even getting yet to the huge volumes of just outright noise in the genome that doesn't ever lead to polypeptides, let alone to ones that might actually wind up part of a protein that actually does anything useful...
... no suggestions, no. Just something that's occurred to me. Rube Goldbergesque... but not quite that either, since biological systems do have a certain elegance to them, as well, despite their frequently cobbled-together quality.
Posted by: Bodach | December 7, 2009 1:39 PM
New t-shirt:
It's exaptation all the way down.
Thanks, PZ!
Posted by: Peter Ashby | December 7, 2009 3:30 PM
@David Marjanović, OM
The New Scientist site allows you to follow individual threads easily and even by RSS individually so it is trivial to follow different threads or you can just view all of them in sequence as you please.
It is therefore perfectly possible to do it on the web. Having used and continuing to use the NS site has further convinced me that it would indeed be beneficial.
Posted by: Lynna | December 7, 2009 4:01 PM
I finally had time to give PZ's summary and associated PDF some attention today. I have to say, "Bravo!" I copied the post and sent it, along with some comments, to my daughter and my son.
The simple examples for Excitability, Synaptic Signaling, and Pathfinding were well within my scope of understanding. I got it. My byblow brain is excited.
Posted by: Qwerty
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December 7, 2009 7:15 PM
I was at the talk as one of the non-scientific attendees. Anyhow, I found the talk a little bit over my head, but I think I understood the gist of most of it.
I thought the questions asked were far more intelligent than most of the questions asked at PZ's "should ID be taught in the schools" debate.
More inquiring questions than the question to attempt to stump one of the debaters.
My elderly mother is having some problems with short-term memory loss. I did want to ask what science thinks causes this but refrained from doing so. My guess would be that our brains just wear out after a certain amount of time.
I'll reread this post and maybe glean a little more knowledge than I gleaned at the initial presentation.
Posted by: RickM
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December 8, 2009 5:51 PM
Well, I guess I'm just going to have to take time to register and add a comment.
Thanks PZ, great post.
Posted by: Bilbo
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January 30, 2010 3:12 PM
Mike Gene's reply to PZ:
http://designmatrix.wordpress.com/2010/01/30/we-need-to-blow-it-off-its-feet/#more-1972