Posted by: Jeremy Fox | June 21, 2012

Darwin’s Origin of Species: notes for your reading group (UPDATED)

I teach a graduate seminar on Darwin’s On the Origin of Species. We read and discuss the Origin and some related readings. It’s a lot of fun, for me and the students. If you haven’t yet read the Origin, or read it when you were too young to fully appreciate it, or haven’t read it in ages and don’t remember it that well, you really ought to (re-)read it. It’d be great choice for a graduate reading group–you could read a chapter a week and finish it in a semester. So here are a bunch of notes to help and encourage you to take the plunge.


  • Read the first edition. Six editions of the Origin were published in Darwin’s lifetime. If you just go to a library or bookstore and pick a random copy of the Origin off the shelf, you’re probably picking up a copy of the sixth edition (if it’s got a whole chapter devoted to refuting the objections of a guy named “Mivart”, it’s the sixth edition). The sixth edition is mainly of historical interest, as the final statement of Darwin’s views. Those views were heavily revised from the first edition, in response to the many criticisms Darwin received. Unfortunately, most of those criticisms were off base, so the first edition actually is more correct than the sixth. So as a scientist who’s likely to be curious about how much Darwin got right, and who probably wants to be able to trace back modern ideas to their Darwinian roots, you’ll want to read the first edition. The first edition also is shorter, clearer, and more tightly argued, making it an easier read. It’s been aptly remarked that the sixth edition could have been titled “On the Origin of Species By Means of Natural Selection and a Whole Bunch of Other Things.” And the first edition is the edition that started the intellectual revolution–it’s the edition that changed the world. So why not read that?
  • Consider which printing of the first edition you want. Darwin’s books have long since gone out of copyright, so you can read the first edition for free on various websites, such as this one. If you prefer a hard copy (and call me old fashioned, but I really think every biologist should own a hard copy), then I recommend The Annotated Origin. It’s a facsimile of the first edition, so it has the original pagination (helpful if you’ll also be reading scholarly articles about the Origin, as they all refer to the book using the original pagination). And as the title indicates, The Annotated Origin has extensive and very good marginal notes from biologist James T. Costa. This is the printing I plan to teach my class from in future. Another option, which I’ve used in my class in the past, is the famous Harvard facsimile edition first published for the Origin‘s 100th anniversary in 1959, which includes a famous and influential introduction by Ernst Mayr.
  • Do a bit of background reading. The Origin is quite accessible. It’s not technical; it was written to be read by any educated person. And while the style may not be your cup of tea (though I actually like it, or at least don’t mind it), it’s not difficult reading. So you can get a lot out of the Origin without doing any background reading. But background reading can definitely help you get more out of it. I require my students to read Janet Browne’s Darwin’s Origin of Species: A Biography. It’s a short (readable in a few hours) introduction to the writing of the Origin, the social and scientific context, reaction to the book, etc. Browne’s mammoth two volume biography of Darwin is great too, but probably much more than you’d want to bite off for a reading group. And of course there are many other things you could read; it’s not for nothing that historians of science talk about the “Darwin industry”.
  • Read it as part of a group. Read the Origin along with others so you can talk about your reactions as you go. Or just read along with John Whitfield, a science writer who back in 2009 did a nice series of blog posts called Blogging the Origin. He read the first edition and did a post on each chapter.

Food for thought

Here are a some suggestions for things to think about as you read the first edition of the Origin. Many of them reflect my own interests, of course, so just ignore them if you don’t share my interests. The Origin is a really rich book and there’s plenty in it for anyone.

  • The quotations with which Darwin prefaces the book.  One is from William Whewell, an influential thinker of the generation prior to Darwin’s, and the other is from the “inventor of the scientific method”, Francis Bacon. Both quotes talk about how science, and scientific laws, don’t conflict with Christianity. These quotes are an attempt by Darwin not just to defend against charges of impiety or atheism, but also to defend against charges of being unscientific. At the time, the leading view on the origin of species was “special creation”, which actually had relatively little in common with the forms of creationism espoused (often in thinly-disguised form) by fundamentalists today. It’s important to understand that “special creation” was just one manifestation of the deep intellectual commitments of most senior scientists of the day. To those scientists, such as the geologist Adam Sedgwick (once a mentor of Darwin’s) the whole point of science was to read nature as the “Book of God”, to document natural order and patterns as a physical manifestation of God’s plan. To someone like Sedgwick, Darwin’s explanation for the origin of species wasn’t just wrong, it wasn’t even the sort of thing that counted as a scientific explanation at all. And conversely, Darwin argues in the Origin that “special creation” is not so much an incorrect explanation for the origin of species, as a non-explanation–it leaves all sorts of surprising patterns in nature “untouched and unexplained”. It’s difficult for a modern reader to really “get” the mindset of a special creationist, but it’s worth a try in order to understand the Origin as Darwin and his readers understood it.
  • Darwin’s style. Note that the style is very cautious and modest (until the final, summary chapter, which is beautifully confident). Indeed, Darwin devotes a whole chapter to raising and then addressing objections to his ideas, and it’s clear from the way he writes (and from private correspondence) that he’s not just setting up straw men. He really does worry about these objections, perhaps even too much. It’s a far cry from the way most scientists write these days.
  • Ordering of the material. Note that Darwin doesn’t start out with anything exotic (nothing about the Galapagos Islands, for instance, which are hardly mentioned in the book). Instead, he starts out talking about domestic animals. It’s an attempt to get readers on board, by talking about something ordinary and familiar. More broadly, note that in the first few chapters Darwin lays out his big conceptual idea–evolution by natural selection–and then in the remainder of the book discusses how that hypothesis fits with and explains the available data. One can ask, as philosopher Eliot Sober has, if Darwin wrote the Origin “backwards”. That is, he starts out with the mechanism of evolutionary change, and only then does he go on to argue for the fact of evolutionary change. Which seems a bit backwards, when put that way–shouldn’t you start by describing what needs explaining before you explain it? You may want to think about why Darwin ordered the material the way he did.
  • What Darwin got right, and wrong, and the risk of mixing them up. Darwin gets a lot right in the Origin, including prefiguring almost every big idea in modern ecology (even trendy ecological ideas like biodiversity and ecosystem function!) My students are always shocked at just how much he gets right and how modern he sounds. He also gets some things wrong, of course (and not always because he was unaware of facts we’re aware of). But he gets so much right that it’s tempting to read into the Origin modern ideas that Darwin himself didn’t actually hold. Case in point: the book is infamous for not fully living up to its title because Darwin doesn’t really fully grasp how natural selection can generate new species from existing ones. That’s because he doesn’t really recognize the possibilities of spatially-varying selection (different variants favored in different locations) and frequency-dependent selection (relative fitness of different variants depends on their relative abundances). Instead, Darwin has what Costa aptly calls a “success breeds success” vision of how selection works–new, superior variants arise and then sweep to fixation everywhere they can spread to, replacing the previous variants. To get this “success breeds success” process to generate and maintain diversity, Darwin invokes what he calls his “Principle of Divergence”, which is the idea that parents will be fitter if they have divergent offspring (offspring that differ from one another in their phenotypes). The idea is basically to make the production of diversity itself a cause of evolutionary success. There are contexts in which this can work–but plenty of contexts in which it can’t (there are logical as well as empirical flaws to the idea as developed by Darwin). Now, I should note that I’m not an evolutionary biologist, and there are evolutionary biologists who read the Origin as presenting pretty much a fully-modern and correct theory of how selection affects speciation. All I can say is that I think they’re reading into the Origin, and in particular into the “Principle of Divergence”, something that just isn’t there. Read it and judge for yourself.
  • Explanation and unification. It’s often said that Darwin’s great achievement in the Origin is to unify and explain many apparently-unrelated facts. The Origin links together and explains facts about everything from animal breeding to biogeography to embryonic development to the fossil record. Which raises many deep and interesting conceptual issues. For instance, is unification always a good thing in a scientific theory? Why? Is it because unification is a mark of truth? For instance, maybe unification is a sort of “indirect” or “circumstantial” evidence. If a theory seems to work well to explain facts A, B, and C, then perhaps we ought to take that as indirect or circumstantial evidence in favor of its explanation for fact D. But on the other hand, conspiracy theories also unify many apparently-unrelated facts–which is usually taken to indicate that they’re false, not true! Or maybe unifying theories are valuable because, true or not, they’re more productive as “working hypotheses”, guiding future investigations by suggesting what questions to ask and what data to collect. Darwin famously called his theory “a theory by which to work”. Then again, maybe not. For instance, progress on understanding the causes of variation and heredity (problems that famously vexed Darwin) came not just from the rediscovery of Mendel’s work, but from breaking the problem up and disunifying it. Muller and his followers figured out what we now call transmission genetics by explicitly setting aside and ignoring what we now call developmental genetics, regarding it as a separate problem. And what exactly does it mean to “explain” some fact or set of facts, anyway, and how are explanation and unification connected, if at all? For instance, do explanations have to be unifying if they’re to count as explanations at all? The intuition here is that every theory or hypothesis has to take something for granted. So if you produce a separate, independent explanation for every single thing you want to explain, then you’re effectively just changing the question, substituting one set of unexplained, taken-for-granted statements for another. At best, you’re just pushing the required explanations back a step (e.g., if you “explain” the origin of life on earth by saying “it arrived on an asteroid”, all you’ve done is change the question to “where did life on the asteroid come from?”) But if you have a unifying explanation, a single explanation for a bunch of different facts, you’re “killing many birds with one stone” and reducing the number of unexplained statements we just have to take for granted. See here and here and here for some longer posts I did on issues of explanation and unification for the class blog.
  • Circular reasoning? Darwin developed his theory to explain lots of different facts about the world, and along the way he modified it in various ways as he discovered new facts. In light of that, isn’t it a bit (or even more than a bit!) circular to regard those facts as evidence for his theory, or as a test of his theory? Isn’t it circular (or maybe better, “double-dipping”) to use the facts to develop and inspire your theory, and then turn around and re-use those same facts to test the theory? After all, developing your theory so that it fits known facts guarantees that your theory will fit those facts! In philosophy of science, this is known as the “old evidence” problem: when does previously-known (“old”) evidence constitute evidence for a new theory? There are plenty of examples of the old evidence problem besides the Origin, so it’s a very general issue well worth thinking about (I emphasize I’m just throwing the issue out there as food for thought–I’m not saying whether I think Darwin’s argument is actually circular!)
  • Comparative reception of the Origin. After you read the Origin, you’ll probably find yourself wanting to dig into all sorts of related topics. One related topic my class discusses is the comparative reception of the Origin in different cultures and religions. There are obvious reasons why North American and European biologists focus so much on how Christians, especially conservative ones, react to evolution. But it’s worth remembering that there are other strains of Christianity, and other religions, and it’s very interesting to compare and contrast the ways they reacted to Darwin’s ideas.
  • UPDATE: Darwin is in the eye of the beholder. Darwin has been claimed as a model and even a hero by many groups. For instance, the Origin has been claimed as a biological justification for both communism and unregulated capitalism. John Whitfield astutely notes that Darwin has been claimed as a model by both the “lean and mean” school of evolutionary biology (theorists like Fisher, Hamilton, Maynard Smith, Dawkins, and Price, who focused on natural selection and its consequences using simple, elegant models) and the opposing “let a thousand flowers bloom” school (exemplified by Stephen J. Gould, with his emphasis on historical contingency and the complex interplay of many evolutionary forces). Darwin has of course been claimed as a model by naturalists, especially those who bemoan the perceived decline of field-based, observational natural history within biology. Even though Darwin himself did a lot of highly artificial greenhouse and lab experiments to which he attached great importance, wasn’t above collaborating with mathematicians (as in the section of the Origin in which he builds a geometry-based model of how honeybees can build perfectly hexagonal honeycombs), and was heavily criticized in his own time for engaging in ungrounded theoretical speculation rather than sticking close to the data and making inductive generalizations. Interestingly, many of today’s greatest naturalists, like E. O. Wilson and the Grants, achieved their greatness in a similar way, by seriously pursuing and integrating many different lines of work of which “natural history” was only one. So when you read the Origin and come to see Darwin as your hero (as you probably will!), pay attention to what you find heroic about him–it may well say more about you than it does about Darwin!


  1. The Variorum edition by Morse Peckham is simply colossal… awesome; edited more than half a century ago, I just can’t imagine the amount of effort needed to complete the work, in an age without computers…

    • Yes, an amazing piece of work, but strictly for scholars! (for those who don’t know: the variorum edition tracks every single edit to the text that Darwin made through all 6 editions)

  2. Off-topic, but I can’t resist.

    Small world, of people and ideas.

    So, I started reading Darwin, and was very soon distracted by Darwin’s reference to Sir J. Sebright. And started Googling.

    “1838 Spring or Summer
    While reading up on animal breeding, Darwin came across a pamphlet written by a politician and professional animal breeder by the name of Sir John Sebright. It was titled “The Art of Improving Breeds of Domestic Animals” (1809). In this pamphlet Darwin was struck by one particular statement which said that the weak do not survive long enough to pass on their traits.”

    Turns out, by sheer coincidence, he’s exactly the same Sir John Sebright that I mentioned in my old post about survivorship bias of old buildings.

    “1. Survivorship bias. Maybe there’s no difference between old stuff and new stuff. Some was built to last, and some wasn’t. But all the old stuff that wasn’t built to last has already fallen down and disappeared, so we observe a biased sample of old stuff.

    From Arthur Young’s 1804 “General View of the Agriculture of the County of Hertfordshire”:

    Sir John Sebright has begun an improvement of a quantity of waste common that he had a power of enclosing without an act of parliament, which does him much credit. He has built a good cottage for the overlooker, a barn, has enclosed a stack-yard, now full of stacks, and built a double range of sheds from the barn to the south, open only on that side for cattle-stalls, stables, sheep-yard, &c. &c. well planned and executed.” ”

    (Now it’s my barn.)

    He’s famous nowadays (in poultry circles) as the original breeder of Sebright bantams. Also for organising the contest between the Norfolk plough and the Hertordshire plough (Agricultural revolution). And the last bare-knuckles prize fight held in England.

    Sorry. Back to reading Darwin.

    • Wow, you can hijack all the threads if you’re going to hijack them like this!

      On survivorship bias, I have an old post on basically the same idea. You often see the idea invoked in an informal way in various contexts in ecology, but rarely do people try to quantify its strength in a rigorous way.

  3. Darwin: “If it has taken centuries or thousands of years to improve
    or modify most of our plants up to their present standard of usefulness to man, we can understand how it is that neither Australia, the Cape of Good Hope, nor any other region inhabited by quite uncivilised man, has afforded us a single plant worth culture. It is not that these countries, so rich in species, do not by a strange chance possess the aboriginal stocks of any useful plants, but that the native plants have not been improved by continued selection up to a standard of perfection comparable with that given to the plants in countries anciently civilised.”

    That is the reverse of the causation put forward by Jared Diamond in “Guns, Germs, and Steel”. Diamond says it’s not “strange chance” but rather Geography, like the East-West vs North-South orientation of continents, that explains the scarcity or plenty of aboriginal stocks of useful plants (and animals), which in turn explains civilisation. I wonder who is right.

    That’s a small point in what is a very impressive section by Darwin. He actually joined two pigeon breeders clubs!

    • Good point, I’d forgotten that bit from Diamond. As to who is right, I’m not sure. In some cases, I think it’s unclear. For instance, domestic dog breeds differ hugely from one another, varying by over an order of magnitude in adult size, the largest range of variation in adult size for any wild or domestic animal species. Indeed, they vary so much Darwin mistakenly thought they must be descended from different wild ancestors. Dog breeds differ from one another much more than, say, cat breeds. But it’s still unclear (I think) just how much of that is due to a longer history of more intense artificial selection on dogs to produce breeds for a greater range of purposes, and how much is due to something special about the ancestral stock (something special about the wolf genome).

      Put another way, if we wanted to, could we breed for 100 lb. housecats?

  4. Darwin: “Pigeons can be mated for life, and this is a great convenience to the fancier, for thus many races may be kept true, though mingled in the same aviary; and this circumstance must have largely favoured the improvement and formation of new breeds.”

    Wow! Does that apply to natural selection too, so that animals that mate for life tend to evolve more quickly than those that don’t? If so, does this create an evolutionary advantage to mating for life (because you can evolve for changing environments more quickly)? Or am I implicitly/illegitimately assuming group selection here? Have biologists studied this (I expect they must have)?

    • Hi Nick,

      Not sure if the specific issue you raise has ever been examined by subsequent evolutionary biologists. It’s really a specific instance of a more general idea, that of assortative mating. If organisms tend to mate with those with similar phenotypes (as when a breeder pairs off a male and a female that both possess some desired trait, and that male and female pair for life), then that can, in combination with the right sort of natural selection, create conditions favoring splitting of ancestral species into new species. A famous example in nature is threespine stickleback in certain BC lakes. There are pairs of coexisting species, one adapted to live and feed in the water column, the other adapted to live and feed near the bottom. The two species look different, and there’s selection against hybrids, which are intermediate in phenotype, and so not well-adapted to either habitat. And females of each species prefer to mate with males that look like themselves, so hybrids are rare (indeed, presumably selection has favored females that make such choices, since otherwise their offspring would be unfit). At least, that used to be the story. But for reasons that aren’t yet entirely clear, the story has changed in the past few years and hybrids are suddenly becoming very common–the two species appear to be merging back into one.

      • Jeremy: thanks! OK, I now see the connection to assortative mating. The question then would be (and one that should be answerable with statistical analysis): in a finite population, and especially in a small population, would mating for life tend to accentuate the tendency of assortative mating to speed up evolution and branching of species?

        My hunch is that it would. Here’s a sketch of the proof: Suppose you were tall, and liked tall women. If you had one child each with the 6 tallest women you could find in the local population, the average height of your children would be slightly smaller than if you had 6 children with the one tallest woman you could find. In the limit, as the population size increased, there would be no difference between the average height of your children under the two strategies. (With a very large number of pellets in the shot gun pattern, the six most northerly pellets would be very close in latitude) But for a small population there would be a big difference.

        In other words, a strategy of mating for life makes mating more assortative. If you instead have a strategy of mating with a sequence of women in their most fertile years (say), you can’t afford to be as picky about their genotype, unless you have a very large population where some sort of Law of Large Numbers applies..

      • I see what you’re getting at there Nick, but I don’t know that I buy it. Your argument confounds changes in the variance of one’s mates with changes in their mean. Ok, I can see why that would necessarily be the case when you’re up against the boundary of the distribution, but it’s not the case in general. And so in a real biological population, I suspect that the effect you’re arguing for wouldn’t be a big deal. But I’ll need to think about it more.

        Side point, just to make sure I wasn’t unclear in previous comments: assortative mating is defined as individuals mating with others like themselves, not as everybody wanting to mate with the most extreme individuals. It sounds like you’re clear on that, just wanted to make sure.

        Note as well that, depending on the biological details, assortative mating can also oppose evolutionary branching. For instance, if like mates with like, mates can be scarce if you’re out in the tails of the distribution, whereas intermediate individuals near the mode have access to many mates. That in itself can create stabilizing selection, favoring individuals with intermediate phenotypes.

      • Jeremy: OK. I’m still thinking this through.

        Let me sketch a different model, which doesn’t depend on finite population size.

        Assume that any individual’s value in the sexual market depends on two characteristics: height (which is heritable); and age. So over time an individual’s value rises and then falls, as he or she ages. But height stays the same.

        Assume that men and women pair off in order of value. The highest value men mate with the highest value women. Medium value men mate with medium value women, and so on.

        If people pair off each year, so the sexual market is an annual market, the rank orderings will be changing over time, as individuals age. We will see pairings between the tall old and the short young, who have equal value. We get imperfect assortative mating by height.

        But if people pair for life, all those entering the market do so only once, and will all have the same age. So we get perfect assortative mating by height.

        (What I can’t figure out is how much this example generalises, or whether I’ve rigged it by assuming height is heritable and age isn’t.)

        God this stuff is interesting, and hard!

      • Ok, I’ll think about that. It’s a bit hard for me as a biologist to think about your example because I think it’s quite unrealistic (it’s not at all like when I’m reading your blog, where I’m perfectly happy to imagine economies based entirely on apples or antique furniture). If I’ve understood correctly, you’re imagining a situation in which there would actually be strong selection against mating assortatively, and strong selection for pairing up with young mates. But I know you’re just trying to make a conceptual point here, so I’ll give it a go.

      • Jeremy: “If I’ve understood correctly, you’re imagining a situation in which there would actually be strong selection against mating assortatively, and strong selection for pairing up with young mates.”

        Hmm. I hadn’t thought about that. I was just trying to show that pairing for life increases assortative mating by heritable characteristics, by eliminating age as a competing factor determining who mates with who.

        But let me now think about it.

        Assume height increases genetic fitness (tall people can reach the higher fruit, so there’s no fruit left for the short people).

        With annual pairing, the tall old would on average have younger mates, so would have more kids than they would under pairing for life. But their mates would be shorter, and so their kids would be shorter than under pairing for life.

        Hmmm. Lets think back to what Darwin said about pigeon fanciers. If relative selection pressures were very strong, so only the very tallest survive (either the pigeon fancier or getting fruit off trees) then mating for life would be selected for. A breeding strategy for quality (in this case height, from marrying the tallest mate) would beat a breeding strategy for quantity (swap your tall old mate for a shorter younger one each year).

        I don’t know. I think it would depend. It’s getting too hard for me.

        (Don’t feel obliged to reply, but thanks for your other replies!)

      • I’ll just wait here while you rederive all of sexual selection theory in your head. Let me know when you’re done. 😉

        I’m just teasing you Nick, it’s great that you’re thinking hard about this stuff, you’d be a great addition to the seminar I teach.

        In response to a previous comment, I’m very interested that Darwin reminds you of Friedman, I of course have no idea about that having never read Friedman. You’re certainly right that Darwin’s is a very “thick” argument (he famously once called the Origin “one long argument”). I’ll look forward to future WCI posts reflecting the fruits of your reading of the Origin.

        Go ahead and keep commenting on whatever you feel moved to comment on, I’ll do my best to keep up. 😉 Or, you can just pick my brain about Darwin when I get to Ottawa July 5-10. 😉

        Once you hit chapter III, where the idea of natural selection is first introduced, I’ll be especially interested in any comments you care to make on Malthus, since unlike the vast majority of biologists, including me, I’m betting that you’ve actually read Malthus, or at least read enough about him to know what he actually said. Biologists only have an nth-hand cartoon caricature of Malthus. Both Darwin and Wallace independently thought of the idea of evolution by natural selection in large part because they’d read Malthus. But then again, lots of other natural historians read Malthus and they didn’t think of natural selection. I do want to try to read Malthus myself at some point, just to get some vague sense of how “obvious” the idea of evolution by natural selection was. Of course, I’m guessing that, given your background, you’ll find that one of the most familiar and therefore least interesting bits of the Origin.

    • I note that this is going to become our longest comment thread ever if you post a comment on every bit of the Origin that intrigues you, and I reply every time. 😉

      Not that I’m complaining (at least not much); always good to see someone enthusiastic about the Origin.

      So, is this your first time reading it?

      • Jeremy. Yep. Like most “educated” people, I have some vague sort of understanding of Darwin, or at least flatter myself by thinking I do. But I’ve never read him. And i don’t ever remember reading any “official” text on Darwin’s theory. It’s only bits and pieces I have picked up over the years from here and there.

        For an example of my ignorance, until very recently, when I read the explanation on Razib’s blog (which I can only understand about half of) I couldn’t figure out how Darwinian evolution was compatible with “Regression to the mean”.

        What most impresses me (so far) about reading Darwin is how “thick” his argument is. He amasses all sorts of evidence and arguments in slowly building to his theory. That is so different from most modern science. (He’s like Milton Friedman, only much more so).

        Plus, the notion that he is not just arguing a thesis but at the same time creating the very categories of thought he needs in order to state his thesis. (Reminds me of Walter Bagehot, who had to create the notion of a central bank, which we nowadays take for granted, before he could argue what a central bank should do, and this while the Bank of England was denying that it was in any way different from other banks.)

  5. So what do you think about the circular reasoning question? And if it is circular to use facts that led to the theory as evidence for it, does he present evidence “after the theory”?

    • No, I don’t think Darwin’s reasoning is circular. At some level, it’s difficult to fit real-world cases of scientific reasoning, like the development of the ideas Darwin describes in the Origin, into neat philosophical boxes. Certainly, Darwin modified his ideas repeatedly in response to new facts, criticisms, and other things. But that process was a rich iterative process that doesn’t really fit into the boxes of either “circular” or “non-circular” reasoning.

      Now that I’ve answered your question, I’m going to go off on some tangents… 😉

      Along the same lines, I don’t think it’s really accurate to describe the development of Darwin’s ideas (before the Origin as well as through the subsequent revisions) as either textbook hypothetico-deductive science (propose hypothesis-test-reject or fail to reject) or as textbook Bayesian updating (Darwin modified his premises in response to new data and criticisms, basically equivalent to changing your priors, a no-no for the textbook Bayesian updater).

      So I guess I don’t feel like it’s easy to neatly summarize Darwin’s “method”. I don’t know that he really had any one “method”, any more than science as a whole has any one “method”.

      Faced with this kind of thing, philosophers of science tend to worry about all the possible modifications of one’s initial ideas that weren’t actually pursued. For instance, Darwin modified his theory to allow a greater role for Lamarckian-type evolution in response to Kelvin’s argument that the earth wasn’t all that old. But in principle (say the philosophers), there are all kinds of other ways Darwin might have modified his theory to account for this new information, so why did he choose the modification he did? This is known in philosophy of science as the Quine-Duhem problem, after the philosophers who first identified it. In most cases, this problem seems like a total non-issue to most practicing scientists. At least, it does to me. But I have trouble articulating why. It just seems like someone who raises this concern has no feel for how scientific theory development and modification actually works, and so worries about all kinds of bizarre, hypothetically-possible theories that no practicing scientist would actually consider. Worrying about the Quine-Duhem problem just strikes me as like worrying about invasion from Mars, or the government reading your thoughts, or that we’re all just brains in vats…

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