Since the Darwin debate between me and Chris has opened out into a discussion of general principles, I'd like to add my penny's worth. Chris says he is arguing on the basis of "what seems most likely", or Bayesian principles. On the other hand, I've already invoked Popperian principles, so let's see how all this falls out.
Jim Clark wrote: > Chris is willing to infer from a generally well-founded model to the > specific case of Darwin, whereas Allen would like to see concrete > evidence with respect to Darwin. Chris responded: > One can only draw the best inferences possible based on the information > that is availabe. Specific concrete evidence is grand, when it exists. > When it doesn't, however, that doesn't mean all bets are off. One should > conclude (tentatively, of course, but we're all fallibilists now, yes?) > whatever seems to have been most likely, given the general information > one has. I guess this means I'm fairly Bayesian, even about history! :-) Well, let's see how this works in the present case. Here's an example given by Chris as one more instance that supposedly supports the notion that Darwin was reluctant to publish his theory because of repercussions that would in some way disrupt his comfortable social position, perhaps by his being socially ostracized: > Note also that (despite his own abandonment of religious conviction) > he never denounced the Church or its teachings publicly. Well, that *seems* plausible. One more instance to add to the others that, on Chris's argument, increases the probability that his view is the most likely explanation for the agreed facts about Darwin's tardiness in publishing his theory. However, let's look at this instance a little more closely. "Darwin never denounced the Church or its teachings publicly." But, unlike some of his followers, Darwin was not a polemicist and there is nothing in his personal history that indicates that he was inclined towards this course of action. He was simply not interested in having a confrontation with the Church. Furthermore, even if he *had* had any such inclination, there's an overwhelming reason why he wouldn't have indulged it his deep concern for the feelings of his devout wife Emma. So when we examine the situation more closely in this instance, the "plausibility" angle begins to look very much more fragile as supporting evidence for the thesis being proposed. (And I think I showed this was the case in other instances when I filled in details around the bare bones that Chris presented.) But even if we consider examples where alternative explanations do not so clearly make the one proposed superfluous, I would argue there's a fundamental weakness in Chris's position. And here's where I invoke the ghost of Karl Popper. Chris has effectively admitted that he can't produce concrete evidence, but he can supply a good many instances for which the thesis supplies a plausible explanation, and that this makes for a strong probability that the thesis is valid. What this boils down to is that we have a theory about Darwin's behaviour, and instances are cited where, if we assume the theory, the behaviour makes sense. Popper calls this interpretation in the light of the theory. However, if we start from the assumption that the theory is true, it is not difficult to find examples of (in this case) Darwin's behaviour which can be presented as being plausible supporting evidence *when interpreted in terms of the theory*. And this can seem quite compelling, especially if, as is so often the case when a thesis is being pursued, other aspects of the situation which show that the behaviour in question can be perfectly well explained without recourse to the theory are omitted. In this way specific examples may be presented as amounting to, at least in probabilistic terms, confirmatory evidence in favour of the theory; i.e., Darwin's behaviour "fits" the theory. Here's what Popper has to say on such situations: "It was precisely this fact that they always fitted, that they were always confirmed which in the eyes of their admirers constituted the strongest argument in favour of these theories [i.e., theories based on interpretations of behaviour in the light of the theory]. It began to dawn on me that this apparent strength was in fact their weakness." How so? Because (to reiterate) if you look at various situations (e.g., the fact that Darwin didn't denounce the Church publicly) and interpret his behaviour *in the light of the theory you have already embraced*, then you will have no difficulty in finding 'confirmations' of your theory. And this is especially so, as so often happens, if you focus on your way at looking at the behaviour in question, and disregard perfectly plausible alternative explanations. In this way one can build up a battery of plausible 'confirming' pieces of evidence, even if not a single one is in itself compelling, or without an alternative explanation. Does the fact that *numerous* such pieces of 'confirmatory' evidence can be presented make the theory more probable? I would argue "no", not just because you are looking at the selected instances of behaviour through spectacles already coloured by your theory but also because multiple instances of uncompelling evidence do not add up to strong evidence. One can develop a strong sense of *conviction* in this way, but I think it is a kind of spurious conviction. With a background of a considerable amount of reading about Darwin over several decades, there was not a single one of the instances that Chris presented as evidence for the thesis he was arguing for to which I felt unable to respond (to coin a phrase -:) ), "I have no need of that hypothesis" in other words, that Darwin's behaviour could be perfectly well explained without recourse to the thesis that Chris put forward. I don't suppose for one moment that what I have written will change anyone's mind on the question at issue. In the end it is a matter of judgement, and I learned long ago to be wary of theories that depend on evidence interpreted (usually with a fair degree of tunnel vision) in the light of the theory it purportedly validates, regardless of how widely-held the theory may be. I'm sure it will be argued that we all, inevitably, look at the evidence through lenses coloured by our own preconceptions, and of course there is truth in this. But to a fair extent we can endeavour to offset this by being continuously aware of it, and making efforts to look at the evidence from different angles. Equally important, we should look closely at the situation which is being presented as evidence for the theory to see if information not being provided by the protagonist puts a rather different complexion on the matter. One last point on the case we have been considering. What *did* happen when Darwin published *Origin of Species* after events gave him a shot in the arm? Great publicity and controversy, denunciation of the book from some quarters but no social ostracism or adverse financial repercussions. His comfortable life went on very much as before in Downe and his village neighbours didn't shun him on account of the anti-Biblical implications of his book. Of course that doesn't *prove* that he had not been needlessly fearing such negative repercussions but it certainly doesn't help the theory. Reference: Popper, K. (1963 [1957]). "Science: Conjectures and Refutations." In *Conjectures and Refutations*, London: Routledge and Kegan Paul, pp. 33-65. Allen Esterson Former lecturer, Science Department Southwark College, London [EMAIL PROTECTED] http://www.esterson.org/ --- You are currently subscribed to tips as: [email protected] To unsubscribe send a blank email to [EMAIL PROTECTED]
