A basic introduction to Evo Devo


I made some more noise for the YouTubes.

Script below the fold for those who don’t want to waste 18 minutes watching!

It’s time to talk about evo-devo. This is the start of my planned series of conversations about this particular discipline that I like very much, and I want to warn you at the start that I’m taking this opportunity to talk about stuff that I enjoy, so it’s going to be very much a personal perspective. You are allowed to disagree with me, and in fact, I’m planning to have live threads after every entry so you can openly argue. It should be fun!
I thought I’d start with the most basic concept of them all: WHAT THE HECK IS EVO-DEVO? That’s a good question, especially since it gives me an opportunity to be opinionated.
Here’s my cynical answer: Evo-devo is a label. It’s a gimmick. It’s PR.
For a little context on why I’m saying that, it’s because I suffered through a decade of being associated with another label, as a New Atheist. It was annoying because it brought a measure of media attention to a few people, but when you got down to it, it was meaningless. There was nothing new about this atheism. When we got together in our secret atheist cabals, we’d all say “I don’t know what’s new here. I don’t know what to say when the media asks us about it, but still, we ought to milk this for everything it’s worth.”
One of the giveaways about evo-devo is when you see it called the “new science of evo-devo”. That’s about as significant as this “new” label on a bottle of shampoo. It’s one of the oldest tricks in the advertising game. What’s new about it? They don’t say. It’s shampoo. Maybe they changed one of the chemicals they use in it. I don’t know, and I don’t know why it should make me want to buy it instead of old shampoo.
My shampoo also says it has an “energising formula”. Maybe we missed a trick; we should have called it the “energising science of evo-devo”. If ever I write a book on the subject, I should tell the copywriters I want to title it, “Evo Devo: New Energising Formula!!”
Note: I’m disagreeing with one word in the cover blurb for Sean Carroll’s Endless Forms Most Beautiful, but really, you can’t go wrong by reading that book. It’s an excellent introduction to the field, even if I disagree with some bits and pieces. In fact, if you haven’t read it yet, maybe you’d be better off turning off this video and going to your library and start re-reading it.
I’m still going to have the effrontery to disagree with some parts of the book. Let’s take a look at a small piece of the introduction.

“The key to understanding form is development, the process through which a single-celled egg gives rise to a complex, multi-billion-celled animal. This amazing spectacle stood as one of the great unsolved mysteries of biology for nearly two centuries [longer than that, and it isn’t solved yet]. And development is intimately connected to evolution because it is through changes in embryos that changes in form arise.”

Yes! Enthusiastic agreement! Development is the core, I agree, and that’s what I want to talk about today. I do disagree to some extent with what Carroll writes next.

“Over the past two decades, a new revolution has unfolded in biology. Advances in developmental biology and evolutionary developmental biology (dubbed “Evo Devo”) have revealed a great deal about the invisible genes and some simple rules that shape animal form and evolution. Much of what we have learned has been so stunning and unexpected that it has profoundly reshaped our picture of how evolution works. Not a single biologist, for example, ever anticipated that the same genes that control the making of an insect’s body and organs also control the making of our bodies.”

I don’t mean to start off so negatively, but one of the things I want to do today is make a case that evo-devo is actually fairly old, as biological sciences go. It’s not that new, and represents an evolution, not a revolution, of our progressive understanding of biology. It also has not profoundly reshaped our picture of how evolution works…that’s hype. It might be literally true that no one realised the extent of our shared genes across phyla, but in part that’s because our understanding of what genes are has only relatively recently become something more than an abstraction — but natural historians were trying to identify a unifying principle behind the organisation of life on Earth over 200 years ago, so it’s a bit unfair to accuse Geoffroy St Hilaire or Ernst Haeckel, for instance, with a failure of imagination, when their flaw was usually an excess of imagination, pushing the evidence beyond what was reasonable for their era.
What’s great about it is that it represents a synthesis, the bringing together of the dual strands of evolutionary biology and developmental biology, combined with the amalgam of genetics and molecular biology. Rather than being revolutionary, it’s more the natural outcome of the progression of science; after all, that unity of genes has been around for a billion years, it’s just that we’re only now acquiring the ability to see it. To do evo-devo, you need to have an understanding of multiple complex disciplines, and you need to appreciate how they complement each other. That’s the real power of the science.
However, lots of sciences do that. For instance, biochemistry and evolutionary biology go together beautifully — there’s a large literature on the evolution of metabolic pathways that’s fascinating and has brought a new understanding to our knowledge of life on earth. We just don’t have a catchy pop-culture label to attach to it. Evolution is such a central idea to all of biology that you can take any sub discipline in the field — say, physiology or genetics or immunology or epidemiology or microbiology — stick an “evo” in front of the name, and you would have a valid subject name, and you’d be able to find researchers who are actually working in it.
OK, one exception: if you stick “evolutionary” in front of “psychology”, you get a lot of junk science.
Basically, the “evo” in the name is redundant. Nothing in biology makes sense except in the light of evolution, a phrase I heard somewhere, which means that “evo devo” reduces to just “developmental biology”. If you can’t get excited about developmental biology (which you should!), then you shouldn’t get worked up about evo-devo. Which gives me an idea: I hear a lot of students complaining about taking biochemistry because it’s hard and seems somewhat abstract and hard to relate to. Maybe if we called it “Evo Biochem” it would generate more enthusiasm without actually having to modify the content of the course.
See? It’s PR. Nothing wrong with that, but just know that “evo” is universal and makes everything cool.
That doesn’t mean that evo-devo is superficial, though. To return to an earlier point, evo-devo is a synthetic discipline — it brings multiple lines of thought together to generate new ideas. In addition to the obvious combination of evolutionary and developmental biology, evo-devo also integrates molecular biology and genetics. That’s what makes it exciting — energising, even — that all these approaches have a multiplicative effect, creating a more powerful tool for studying biology.
But the core of evo-devo, the thing that makes it unique, is development. It’s why I’m in this business, and it’s what makes me, personally, excited about evo-devo. I have to explain how I ended up here.
Probably the first big influence on me, and also on the biology of the time, was John Tyler Bonner’s On Development. I remember wandering through the bookstore at DePauw University as a first year college student, bored because I hadn’t yet taken a course in biology (first I had to get a foundation in chemistry and math), looking for something to remind me why I was a biology major, and there was this slim grey book. It was fantastic. Written by a biologist who studied cellular slime molds, it got right into the key questions of the field. Once I had the opportunity to work in a research lab, I gravitated towards the developmental biology labs, and never left. I strongly recommend this text even now, if development interests you at all.
It’s also important because even now evo-devo is too strongly focused on animal development. Taking a little time to focus on non-metazoan eukaryotes is a good step towards broadening your perspective, and Bonner writes about development in unexpected places, like protists and viruses and fungi, and even in the differentiation of castes in ants.
This is actually my well-worn original copy, purchased 45 years ago, with the cover starting to fall off. I blame this book for shaping my views for almost half a century, and recommend it without reservation, especially if you want to learn about the real breadth of developmental biology. We otherwise tend to get carried away with enthusiasm for charismatic megafauna, like fruit flies and spiders.
The second big influence is this one: On Growth and Form, by D’Arcy Wentworth Thompson. I don’t know a single developmental biologist who hasn’t read this book and been blown away (I know they’re out there, I just don’t want to know them. Joke.) This is NOT an evo-devo book. The first edition came out around 1914, and Thompson is not very impressed with this new science of genetics, and it shows. Rather than genes, he attributes form and pattern to elegant mathematical properties of organisms. But it’s beautiful! Variation in form becomes a mathematical transformation built on universal rules. It also expresses the most important idea in understanding life that I know:

Everything is the way it is because of how it got that way.

I’ve seen that quoted all over the place, but have been unable to find it in the text. I think it’s one of the emergent properties of the work that didn’t need to be explicitly encoded. It’s everywhere. It’s the idea that what you need to know to understand an organism isn’t teleological, it’s not it’s purpose that matters, but the process that produces it. When asking why an elephant has a trunk, explaining what it does for the animal isn’t as profound as figuring out how it is constructed, on either a developmental or evolutionary scale. Prioritise process over utility. Focus on mechanisms rather than on what you think it’s for.
That’s about the most profoundly evolutionary principle I can think of.
Incidentally, a few years after reading Bonner, I picked up this book, Ontogeny and Phylogeny, by Stephen Jay Gould. It’s another one I recommend highly, and which was strongly influential on the forming discipline of evo-devo. I have to point to the dedication of this book.

To the Philomorphs of Cambridge, the world, and beyond, where D’Arcy Thompson must lie in the bosom of Abraham.

The intellectual lineage of evo-devo is deep, and I do think it’s a mistake to label it as new.
There’s another phrase I want to highlight, because it’s also important. It was written in 1973 by Leigh Van Valen, although I didn’t read it until I was in grad school.

Evolution is the control of development by ecology.

That’s beautiful, and it ties the whole story together. Development is one piece of the puzzle, and you have to combine it with ecology and evolution to get the full picture. It only took me a few decades to appreciate the importance of this aphorism — it’s why I’ve recently begun working on spiders, because they add variation and environmental influences to the study of development, and I’ll be returning to this theme later in this series.
OK, I’ve been ragging on Sean Carroll about his use of the term “new” for a while now, and he’s smarter than I am, so I should acknowledge that there is a sense in which he’s right. The current implementation of evo-devo is strongly dependent on the one-two punch of genetics and molecular biology applied to the long standing questions about the development of form, and that combo is more recent. If I had to pin the emergence of that discipline to a single event, I’d have to say it arose with the saturation mutagenesis experiments of Christiane Nusslein Volhard and Eric Wieschaus in the late 1970s and 80s, and the amazing results they obtained. Of course, you can trace the ideas in those experiments back to Lewis in the 1960s and Bateson in the 1890s, but Nusslein Volhard and Wieschaus ripped the whole topic wide open with some remarkable analyses.
But I’ll talk about that next week. Stay tuned. Click the subscribe button.
So, a word about what I’m trying to do here. It’s not as if having me lecture at you from a computer screen is an adequate way to teach, so something else I’d like to do is have a discussion with viewers about the ideas I’m talking about. So I’ll have a livestream on Friday at noon my time to talk about this subject further, to take questions and to get feedback.
Be sure to have read all the books I mentioned by then. (No, not really, we can talk in a general way about the ideas. Don’t panic. No homework. No tests.)
On Friday, I’ll also post a link to the specific paper I’ll be discussing next week. That’s my plan for this series, anyway: I’ll do a solo talk about some paper in evo-devo midweek, have a discussion about it at the end of the week, and also let you know then what I’ll talk about the next week. From now on I’ll narrow the topic to some specific paper in the field, unlike this ramble through general background. We’ll see how well that holds up after contact with the reality of YouTube and fickle audiences. Click on subscribe if you want to follow how this experiment proceeds!
In particular, I’ll announce up front that creationists and conversations about creationists are not welcome here. Real science doesn’t waste time with those bozos, so let’s confine ourselves to the good juicy stuff here, OK?
Thanks very much to my patrons who have been supporting this outreach work. If this were a medium that allowed this kind of thing, I’d encourage you to applaud for the people you see scrolling by. Thanks again, and if you want to help out, you can join them at patreon.com/pzmyers. Or click on the thumbs up down below, that’s good enough.
Also, what you see in the background is the view from my home office window. I get to watch birds when I’m bored, even if I’d rather be looking at spiders right now.

Books cited:

Endless Forms Most Beautiful: The New Science of Evo Devo, by Sean B Carroll

On Development: The Biology of Form, by John Tyler Bonner

On Growth and Form, by D’Arcy Wentworth Thompson

Ontogeny and Phylogeny, by Stephen Jay Gould

Comments

  1. PaulBC says

    The key to understanding form is development, the process through which a single-celled egg gives rise to a complex, multi-billion-celled animal.

    A sneaking suspicion I’ve developed while reading evolution blogs and creationist comments is that many non-biologists, and creationists in particular, remain vitalists at heart and believe that this process occurs by magic and requires some kind of pixie dust (élan vital).

    At the very least, they haven’t given it much thought at all. Because if they had, they would consider it at least as amazing as evolution that a single cell can turn into an elephant, and that somehow even those ivory tusks are implicit in the genes in that cell. It seems a lot more amazing to me, anyway. (And no, I do not believe vitalism is necessary to explain it.)

    It is true that the process can be reproduced reliably, but that’s a far cry from understanding it in detail. For reasons I don’t fully understand, the demise of vitalism is not considered as big a threat to religious faith as evolution. That may be the fact that it does not deal with origins. But I think another reason is a lot of creationists still believe in vitalism and this implicit belief goes unaddressed.

  2. Owlmirror says

    For instance, biochemistry and evolutionary biology go together beautifully — there’s a large literature on the evolution of metabolic pathways that’s fascinating and has brought a new understanding to our knowledge of life on earth. We just don’t have a catchy pop-culture label to attach to it.

    Evo-chemo. You’re welcome!

    Nothing in biology makes sense except in the light of evolution, a phrase I heard somewhere

    Why do you hate Theodosius Grygorovych Dobzhansky?

  3. PaulBC says

    John Morales@4 The first thing that comes to my mind is the band that was popular in the 80s, but I knew PZ was referring to development.

    But it feels as though it should be, naively.

    Though I wonder why naively people would think that. Like most processes, evolution is memoryless. A gene does not carry its complete history along with it, so how would it run “in reverse”?

    I agree that people may have thought this was reasonable, but it’s less naivety than a completely unnecessary belief in evolution as a process of “advancement.” I can also see how people would find that idea reasonable, but mainly because a lot of this was really mysterious before the idea of an information-bearing molecule, at which point it should be clear that there is no secret record of “primitive ancestors” (at least nothing like a complete one).

    (And I think this devolution thing was one of the ideas in Piers Anthony’s Macroscope, which is in retrospect an even sillier book than I thought at the time, but I would still like to find a copy to reread one of these days.)

  4. chrislawson says

    PaulBC, I think you must be a masochist. I would be trying to protect people from reading Piers Anthony in the first place, let alone going back for seconds…

  5. wzrd1 says

    One of my biological jokes is, life’s singular innovation that’s made complex life forms possible is replicated across all scales – the not so simple capability to make tunes of arbitrary sizes. From intracellular size microtubes to megastructures like an abdomen or trunk.
    Think that’s not singular? Show me a rod, show me an I beam.

    Yeah, a rod can be made from a filled in tube, but trying to even theorize signaling to make an I beam, therein lies the path to insanity or creationism, but then, I repeat myself.

  6. PaulBC says

    chrislawson@6 It’s one his earliest works and has some interesting bits about Sidney Lanier. Have you ever read it? But yeah, maybe on the second try I would not like it. I have not read much of his fantasy. Someone lent me “On a Pale Horse” way back in college and it was OK but just run of the mill supernatural. Macroscope has more of a sense of wonder (or so I imagine it to, but that’s why I’m curious now).

  7. says

    A great start, you are much more coherent when speaking to the camera than the rest of us, and the book recommendations are excellent. Wonderful clarity, breadth and wisdom. Remember how riveted I was by Bonner’s work when I was introduced to it in graduate school way back when. I may not be able to do the readings for this but will look in from time to time.

  8. says

    PS It was called “comparative biochemistry” when people compared biochemical pathways in different organisms back in the 1950s. Once protein sequences became available in the 1960s a number of people (like Alan Wilson and Walter Fitch) moved from that field to become pioneers of molecular evolution. But the pathwayness part got lost for a while when they did. However wonderful people like the late Monica Riley kept working on comparative biochemistry — she made a database of reactions in E. coli which connects to other databases of comparative information. You’re right, they should have called it “evolutionary biochemisty” or evo-bio-chem.

  9. says

    It was also called comparative embryology before it became evo devo, and you mostly did it by spending long summers at a marine station fishing up exotic invertebrates. The good old days!

  10. hemidactylus says

    I haven’t given this field much thought for years. Rudy Raff (RIP) and Brian Hall were great promoters (pun) of this region of intellectual discourse. I think it was Hall who got me interested in the quite discrete morphological jumps of turtle carapaces and pocket gopher cheeks.

    Garstang was another early proponent who flipped Haeckel’s dictum on the relation between ontogeny and phylogeny saying in effect the former causes the latter.

    Your quote of “Everything is the way it is because of how it got that way” sounds profoundly philosophical and I mean that in a good way. Pattern vs process? Being vs becoming? Permanence vs flux? Ontology as a matter of mechanistic unfolding?

    I think being vs becoming may have enthralled Heidegger and some existentialists who took it a bit far.

    Is Hoxology the key to all knowledge? And the underlying duplication and divergence that facilitated cooptive functional shifts in the mode of exaptation? Oh no (pun) Gould and Vrba.

  11. hemidactylus says

    Vitalism was a ghost that would haunt biology for years. Yet Driesch was still a great pioneer in the field (alongside Roux) that was haunted by Papa Haeckel’s specter and kicked to the curb by genetics thanks to the three great rediscoverers of the monk’s work. Bye bye plastidules and perigenesis (and Darwin’s adjacent folly).

    Yet vitalism seems to live on subtly as organicism (Mayr?) and emergence. I used to just intuitively “get” the latter as a self evident truth. Seems hand wavy reduction avoidance anymore. Sure water is wet. So what?

    Mayr would bash bean bags and thought eye evolution more convergent than it actually was. He also resurrected the zombie of Haeckel in his recapitulatory concept of the “somatic program” after some quite apt apologia. Mayr did catch the evo-devo bug towards the end of his quite long and awesome career.

  12. PaulBC says

    hemidactylus @13

    Yet vitalism seems to live on subtly as organicism (Mayr?) and emergence.

    Maybe “emergence” is vague enough to mean different things to different people, but I consider it the exact opposite of vitalism. Vitalism is the belief in some addition “vital force” directing development, while emergence is the understanding that it all comes from uniform natural processes, albeit in an indirect way.

    There’s something counterintuitive about the fact that an apparently uniform process can break symmetry in surprising ways and generate structure. I.e., if I start with a cell that can make a copy of itself, I would naively expect it to make a big blob of the same kinds of cell. If the cells have some ability to influence neighboring cells produce differential expression I might think, OK a weirdly variegated blob, but still a blob.

    Instead, we get complex interacting structure and ultimately features that are very far from blob-like. Kidneys full of nephrons, tiny structures, each more sophisticated than a dialysis machine, or macroscopic features like the lens in an eye. When I see a manufactured lens, I can imagine a set of instructions that explain how to obtain the optical material and grind it to the right shape. It is all pretty clearly directly towards the end of getting functioning lens.

    But the DNA of a lens-bearing living thing has nothing like that. It encodes proteins. These differentiate the expression of nearby cells. At a certain point, glands begin to develop and send out signals according to yet another process. These are carried by the circulatory system to receptive tissues, producing non-local effects. In computer science terms (because that’s what I know) it’s a mindbogglingly layered bootstrapping process.

    When I say “emergence” what I mean is that the DNA sets a process in motion that can produce something like an eye or a kidney. That process is entirely explicable in terms of natural law. However, the connection between the “description” in the DNA and final result is so indirect that you really have to go through the whole process, much as you may have to go through the process of applying the steps of a Turing machine to an initial string to determine its final outcome.

    There is no way to look at it and “get the general idea” the way I might do an engineering document on how to make a dialysis machine or a camera lens.

    It has fascinated me since I first read Andrew Hodges’s biography of Alan Turing that Turing wrote a paper called The Chemical Basis of Morphogenesis. I have tried to read it, but I his explanation in terms of differential equations makes it tough-going (for me anyway). While it may have been the most conventional framework at the time. I think cellular automata models and probably L-systems capture the same qualitative way in which structures appear from uniform rules.

    The fact the structure emerges in surprising ways from uniform rules is completely repeatable and can be demonstrated in many contexts, natural (Giant’s Causeway or a cornstarch model of it) and computational (Game of Life and other cellular automata). So I think it is unfair to suggest emergence is anything like a form of cryptovitalism.

  13. PaulBC says

    hemidactylus@13

    I used to just intuitively “get” the latter as a self evident truth. Seems hand wavy reduction avoidance anymore. Sure water is wet. So what?

    I wanted to address this specifically.

    Obviously if you just say “it’s all emergence” you are no better off than “God did it” in terms of actually understanding what’s going on. But without a framework of emergence, you would find yourself looking for things that make no sense, like the “gene for hating asparagus”–which is not to say that there is nothing to find in genes, but it will not be nicely indexed. It would make as much sense as “finding Nemo” in Pixar’s code base. I mean, Nemo’s there somewhere and actually in a far more direct form than you’ll find anything similar in clownfish DNA, but still, to get the motion and lighting effects, you have to go through a rendering process. It is only in the steps of the process that you get anything. If you look at the files, you will just see bytes.

    What would you propose as an alternative? Most people who study emergence actually do try to simulate emergent processes. One could imagine a future supercomputer capable of simulating embryonic development well enough to get from a zygote to an adult, but this is science fiction today. Think of all the hurdles. To begin with, you have to have cell differentiation. But once you have some structure, it only gets more complicated. (The subject of XY-females has come up in other contexts here, but it’s not the “Y” than makes male phenotype, that just triggers a more complex cascade involving the fetal endocrine system–or sometimes doesn’t.)

    In short, you really can’t get around the fact that at a certain point, you need to abstract away the underlying cause and work at a higher level. It is all “reducible” to physics and chemistry, but it is unreasonable to expect to grasp the whole without treating each level as a separate discipline. A film critic will do better by watching a Pixar movie than applying the most painstaking code review of the animation software.

  14. PaulBC says

    @13

    Sure water is wet. So what?

    Last point (and sorry I got going; I feel strongly about this). If you want to study “wet” then you need a lot more than water. You need a comprehension of your tactile sense, the way it is processed in the brain, some observations about what we really mean by “wet.” The feeling of being immersed in water is very different from coming in from a rainstorm with soaked clothes. At a low level, you might look at the effect of surface tension. At a lower level, you might look at H2O as a polar molecule. The cooling caused by evaporation is another thing that figures into what we mean (in the wet clothes scenario, but not the immersion scenario).

    The point to emergence is that the concept (if you think you can nail one down for “wet”) requires many interacting components and cannot be treated adequately just by looking at the physics and chemistry of water. You can certainly give up and say “So what?” You can’t understand everything, so it is often a reasonable reaction, but the realization that something may be too complex to grasp with a reasonable amount of human effort is not “the science of emergence.”

  15. hemidactylus says

    A cell’s overall character (oh no is he applying virtue ethics to development?) is a combination of its history and where it finds itself. So a cell retaining some potential to differentiate will be exposed to its current surroundings, often “interacting” with other cells and via stuff that happens at the surface (a combination of phospholipids and DNA product protein stuff) a signal will meander its way into the nucleus and influence which subset of genes gets epigenetically methylated (canceled) or expressed. It apparently reduces ultimately to gene action (or inaction). We may methodologically impose a construct such as emergence to make sense of it all. Cells themselves are a “level” as are tissues etc on up to ecosystems, but are these levels ontologically real? I guess I’m splitting hairs for fun and inspiration.

    I also assume emergence tries to have it both ways between reductionism and holism. The whole is greater than the sum of the parts. And Durkheim is a great example of the excesses of the latter (holism), using a sui generis ontological construct to black box what is going on inside noggins as would Skinner. But methodologically socifacts and operant conditioning have great utility.

    Now with PZ’s bugbear of ev psych. It is kinda stuck methodologically between levels of culture (which it demotes as so much Durkheimian bluster) and the brain, which it blackboxes with the construct of a computational (substrate agnostic) modular mind. Sure evolved behavior is at the root so much neurons and goo but can psychology really function so deeply removed from its actual arena? Anyway methodologically we have overt behavior of WEIRD students subjected to various experimental designs or surveys and the imposed construct of modules reflecting the savannah EEA. Oh and the ultimate reduction of selfish genes because Dawkins.

    Yet do these “genes” match up to the stuff that engages in mundane day to day molecular housekeeping? Or were they as Gould implied a reified accounting sleight of hand? Methodological convenience slips ever so seductively into an ontological lens and launches a career and eventually a psychological field of study?

  16. consciousness razor says

    Maybe “emergence” is vague enough to mean different things to different people, but I consider it the exact opposite of vitalism.

    You only sort of briefly touched on the point at the beginning here, but you could drop the “maybe” stuff: it is in fact the case that it’s vague enough to mean different things to different people. (So laying out your own view isn’t actually sufficient.)

    Some use it in more or less the same way you do, if I’m interpreting you accurately. That is, it’s not really a kind of “reduction avoidance” because emergent things/properties/etc. do in the real world reduce to the fundamental physics at microscopic scales. We just don’t generally know enough about large and complicated physical systems for this to be especially useful to us. So instead, the story is that we talk about stuff which is still to some extent explicable according to other (non-fundamental) laws/etc. that we’ve developed to describe those things at an appropriate scale. You get a working explanation out of that, which isn’t necessarily saying anything that it is strictly speaking false. But in any case, it’s understood to depend on the fundamental physics which might be extremely difficult (or practically impossible) for us to use in an explanation of such phenomena. So there genuinely is a thing from which the emergent thing is said to “emerge,” and that’s what it is.

    For others, “emergence” means something very different, because they think the reductionistic view I just described is simply false. So, for example, scientific unification isn’t possible, and you may hear about things like “top-down causation” and whatnot. Notice that accordingly there isn’t actually a thing from which it emerges, in this case. In a way it’s like dualism and also involves just as much hand-waving, although it is often using some slightly more up-to-date $5 words rather than the more traditional ones.

    There are various other ways people use the term too, because it’s just not a terribly precise term. For instance, some don’t think spacetime is fundamental (or sometimes it’s one or the other separately). So the thought is that it’s supposed to somehow “emerge” (because they’re not denying that it exists, only its status) from something fundamental that isn’t spatiotemporal. How that is supposed to work, I’ve never been able to understand, but in any case, that is the claim. I’m treating it a little differently here, since this isn’t quite the same dispute as one that deals with how biology or psychology or whatever relates to physics. Instead, it’s about what physical theories themselves should be saying about the things in their own ontologies. But I don’t know … maybe it’s not really so different, because it seems like we still have all of the same important/relevant questions to ask.

  17. PaulBC says

    CR@19 Well, I will avoid an argument about the “correct” use of words.

    I think the increased use of computer simulation is inevitable. Unlike considering a problem “solved” if there’s a closed form or “stamp collecting” if its analysis is intractable, there is clearly a lot of middle ground left in which you can understand something even if by “understand” what you really mean is that you can build something like it and reproduce qualitatively similar effects. (Some of which you can even analyze with closed form solutions.)

    There is certainly a field of “emergent systems” that applies this approach, and that’s what I mean.

    This is of course not new, though it is portrayed horribly in popular culture. Jeff Goldblum in Jurassic Park. (“All the cool mathematicians don’t bother proving theorems anymore. They use computers… because chaos. Chaos!”) It is also portrayed horribly by real-life people like Stephen Wolfram. (And of course there are tons of mathematicians who continue to prove theorems, as well as others who may use computers as necessary.)

    It is kind of a big deal to me, because I always liked emergent systems but my education in theoretical CS really drummed in the idea that all that was silliness and what really counts is a nice proof… by induction or better yet an amortized analysis. What it does on a real computer is largely besides the point (constant factors, implementation difficulty, etc.). If I had it to do all over again, I think I would have followed my instincts and gone with the fun part.

  18. consciousness razor says

    there is clearly a lot of middle ground left in which you can understand something even if by “understand” what you really mean is that you can build something like it and reproduce qualitatively similar effects.

    But that’s not what I mean by the word “understand.” If you can build something like AlphaZero, for example, that doesn’t mean you “understand” the games of chess, shogi, or go; nor did you “explain” anything to me with this procedure of building a thing that can play them well. I know what I mean by “understand” and “explain,” which I think is very close to what most other people typically mean, and that sort of thing certainly doesn’t cover it.

    Making that sort of move looks awfully suspicious to me. Suppose I said “Trump legitimately won the 2020 election,” but what I really meant by this is that he didn’t legitimately win the 2020 election yet might somehow take control of the presidency. It would be totally appropriate for you to correct me on this. And it wouldn’t be kosher for me to respond that I’m just using my words in my own idiosyncratic way, which may suit my purposes while confusing everyone else. There comes a point where we just have to accept that there’s too much of disconnect between the meaning of the words I chose to use and what’s actually true in the real world.

  19. PaulBC says

    CR@21

    But that’s not what I mean by the word “understand.”

    Fair enough, but there’s really a limit to what any individual will ever understand. It doesn’t need to block a discovery process.

    One of my peeves is when I hear someone say “We now know how [something] works.” (bumblebee flight, neutron stars, whatever). Who’s we? Do you know how it works. There is no collective human brain and we have to go through this process as individuals. There’s also not enough time, and almost certainly not enough cognitive capacity to understand it all.

    I’m happy to amuse myself with tinkering. I can imagine larger intelligences, whether it’s like the ship minds of Iain M. Banks or some very intelligent ET who actually get a lot of this. I am not one of them.

    I am really happy, for instance, when I understand how a heavy object hitting a lighter one makes it move forward at twice the speed, after someone once explained the trick to shifting frame of reference so it’s like an object hitting a wall and bouncing back. (I “get” it and I don’t even need to work through the equations of motion.) On the other hand, I could plant a potato in the ground and grow some potatoes, and fuck only knows how that works. I will almost certainly never know the half of it. But that makes me happy too.

  20. PaulBC says

    … I would add that I can understand some part of the whole process and simulations help (which is what I was getting at in @20). Simply being able to turn the crank is not understanding, but models can test hypotheses and you can internalize the models to the point where you have some ability to make predictions about novel instances without going back to a simulation. Even “understanding” something as seemingly cut and dry as Newtonian mechanics is misleading. Rigid bodies aren’t really rigid. I mean it looks nothing like we (or most people anyone) usually think of it. But still, there is something to understand. I limit my expectations to distorted and pinhole views of reality. I still believe there is something to it.

  21. hemidactylus says

    In retrospect maybe I shouldn’t have hitched emergence to vitalism. Paul makes good points.

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