First, apologies to Shari, I only did a so-so job of keeping my mouth shut in class today. I will try to do better at keeping mum in future. Despite that, I do think we had a good discussion which raised a lot of issues that are well worth thinking about. A few further thoughts, in no particular order:
1. Darwin begins his introduction by emphasizing that he's not going off half-cocked--he's thought long and hard about the species problem and isn't being hasty. Clearly, Darwin was concerned with the reception he was going to get.
2. I find it both impressive and amusing that Darwin considered this book an abstract, far too short to include the many facts he'd collected to support his hypothesis. One can easily understand his reasons (see #1), but one can also be glad that he had an editor who recognized that at some point additional facts stop adding weight to the argument and instead end up obscuring it.
3. Interesting, in light of modern arguments about whether some version of creationism can/should be taught in science classes, to see "special creation" treated as a testable scientific hypothesis (and rejected not so much because the facts disprove it, but because of its failure to explain phenomena that Darwin's theory explains). Many scientists today would argue that creationism is not a scientific hypothesis at all, so that it doesn't make sense to talk about evaluating it as such. My own view is that creationism could be (and has been) pitched in both ways. For instance, if a creationist says that the world was created by God to appear as if evolution by natural selection had occurred (e.g., God created fossils in order to fool paleontologists), then that's not really scientific since the "hypothesis" is defined as "whatever's consistent with any conceivable evidence."
3a. There's a connection between #3 and long-standing philosophical issues of evidence and confirmation. Is it always bad for a theory to be consistent with the evidence "by definition"? What if a theory is developed in order to explain certain known facts, as Darwin's theory was? To what extent (if any) do those same facts count as evidence in support of the theory? After all, if the theory was developed in order to explain known facts, it couldn't possibly be inconsistent with those facts, so isn't the theory guaranteed to be "supported" by what's currently known? Put this way, it sounds like previously-known facts shouldn't count as evidence in favor of a theory. But there are many, many cases--The Origin being one example--in which known facts have been interpreted as supporting a theory that was developed to explain them. What justifies this? Is it that Darwin's theory can explain a wide variety of apparently-disparate facts, thereby "unifying" them? Does "unification" count as evidence in favor of a theory? Think of the common phrase "That explains a lot"...
4. Darwin is clearly worried that he can't offer a mechanistic theory of variation and inheritance. But does he really need one? This gets back to the issue of how to establish the domain of a scientific theory--how does one decide exactly what phenomena a given theory should explain/predict/unify? Why couldn't Darwin have said, without apology, "Organisms vary, and offspring tend to (but don't necessarily) exhibit the same variations as their parents. My theory shows how natural selection, acting on heritable variation, can give rise to new species. My theory is silent on where variation comes from in the first place, and why it is inherited. For my purposes, I will simply assume the brute empirical fact of heritable variation, which will hopefully be explained in future by some obscure monk." After all, every scientific theory takes for granted something that is explained by some other theory. For instance, the Modern Synthesis of Darwinian selection with Mendelian genetics takes for granted the underlying molecular and developmental mechanisms that drive transmission and development, and simply deals with the consequences of those mechanisms. At most, it seems to me that Darwin could've just said something about the features that any theory of variation would have to have in order to allow evolution by natural selection to occur (e.g., blending inheritance won't work, because all variation would be quickly eliminated, leaving none for selection to work on).
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6 comments:
The philosophy of 3a interests me and convinces me more of the value of Darwin's theory (but then it would take a lot to convince me otherwise [that is not a challenge])
If a theory was developed in order to explain certain facts then it does make sense that those facts are consistent with the theory.
Where Darwin's theory goes above and beyond is that 150 years later, new facts from new experiments are still supporting observable natural selection. He could not have predicted events 150 years in the future.
Read this article:
B.R. Grant, and P.R. Grant (1993) Evolution of Darwin's Finches Caused by a Rare Climatic Event 251: 111-117
As far as unification counting as evidence in favor of a theory.. I think that so long as that unification makes valid scientific sense that it should be considered a valid theory. The actions of a god can be used to explain a wide variety apparently disparate facts and unify them. This idea as stated before, is not however a valid scientific hypothesis.
I certainly agree that Darwin's theory went on to demonstrate its predictive value (e.g., Darwin's famous prediction of the existence of an as-yet-undiscovered long-tongued moth species). But that doesn't go to the issue of the evidential value of previously-known facts.
Some philosophers have tried to distinguish between known facts that were "used" in constructing the theory (and so can't be said to support the theory), and facts that were not so used. But it's often difficult to say exactly what facts were "used" in constructing a given theory.
Lorraine suggests that there's a difference between unifications that have scientific merit, and those that don't. I'm of two minds about this myself. Part of me wants to say that this notion needs to be fleshed out; what's at issue here is precisely what constitutes "scientific merit." It's perhaps obvious that silly theories like conspiracy theories provide an entirely ad-hoc and illusory "unifying explanation" of different phenomena. But there are plenty of real scientific cases where there's been debate about exactly what facts a theory should be expected to explain. But there's another part of me that's suspects that no clear-cut, universal criteria could ever be provided to distinguish scientifically-mertiorious unifying theories from the other kind. All we can do is collect new evidence and see which theories stand the test of time and which don't.
I really appreciate the comment in 3a. Very interesting - the idea that the theory was developed to support an observation, and then those same observations are supposed to provide the facts that support the theory. Circular argument.
In regards to point 3, I am curious to know how creationism has been pitched as a hypothesis that can be refuted. After all, having faith in something means that you accept it no matter what.
Hi Tonya,
Faith hasn't been universally considered as something one holds independent of all evidence. For instance, natural theology sought in nature evidence of God's hand, based on an assumed ("hypothesized", if you like) view of what God was like and what sort of world he would create. Paley was an eloquent natural theologian, who took the existence of complicated, well-adapted organisms as evidence for God the Designer. That's why vestigial organs and "poorly-designed" traits (such as our use of the same tube for breathing and swallowing food, leaving us open to choking) have long been taken as evidence against Paley's ideas and in favor of Darwin's.
One could of course argue that, in their desire for evidence for their faith, natural theologians were not truly faithful, but they themselves wouldn't have seen it that way.
Darwin himself prefaces The Origin with two quotes (from Whewell and Bacon) on the relationship between science and faith. Make of these what you will...
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