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.
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