Even the Good Guys: Extraordinary claims require extraordinary evidence. Really?

Amazingly, it looks like the Australopithecus sediba fossils found at Malapa, 1.9mys old and small-brained but ‘perhaps human ancestors’, might have preserved skin, John reports. But… he blogs, 3rd Sept 2011:

“Suppose it’s really skin, or some other soft tissue, I thought. How would you go about testing the hypothesis? Extraordinary claims require extraordinary evidence.”

But that’s ok, isn’t it? Why believe anything new unless there’s some special reason?

Well here’s why it’s is a huge error to say “Extraordinary claims require extraordinary evidence”… By “claim” is meant theory, so it’s really saying a new theory must explain evidence other theories can’t. Sure, the reverse is definitely true: new evidence unexplained by any accepted theory does need a new theory to explain it, but just because two things go together, “humans” and “mammals” say, because the latter includes the former, it doesn’t mean that relation works in reverse. So, what happens then when you take an interesting new theory with a subtle superiority, to a funder and ask them to resource an experiment? “So sorry – can’t waste money on it – ‘Extraordinary claims…’ and all that!” Not being able to find the special evidence unless you look, perhaps involving an expedition to observe an astronomical transit, will be lost on the funder who, like most will have a slogan-driven philosophy of science. (The problem being, not the right 14 slogans, and not enough thinking used either 🙂 .)

In fact, a new theory that explains just as well as the old theories should be given the same credence. Of course if it has other advantages such as those listed in ж 2: “The worth of a theory depends on such aspects as accuracy, generality, simplicity, and the degree to which its implications are genuine predictions (and the more surprising the better)”, it may well be superior without explaining more! A very unusual theory, if we end up accepting it, will take us far further forward than one just slightly different, which is why more unusual theories are potentially better. And this ‘value of a theory if correct’ should not be confused, as usually happens, with judging whether it is correct.

The Malapa “skin-stuff” actually starts by being a case where we have not an extraordinary theory but extraordinary evidence. The “skin-stuff” hasn’t been seen before, and precedes the skin theory. Looked at like that, the slogan certainly doesn’t make sense since we should have invoked “extraordinary new evidence requires an extraordinary (i.e. new) theory” immediately the “skin-stuff” was found; also, the falsism in its classic form, demanding extraordinary i.e. novel evidence, cannot apply at all since we already have novel evidence.

It could be said that we now seek further more detailed evidence to help tune-up a new skin-based theory to explain the “skin-stuff”. But the need for a new theory was already there, so no point in saying we need more new evidence to justify having a new theory. Which is what the slogan suggests.

But the slogan’s main problem is that it seeks to suppress even the tiniest attempt to develop a new theory. There’s a huge and vital difference between starting to take a theory seriously as a possibility and actually believing it above all others, and this vital middle ground is what the slogan seeks to destroy. Evidence so often can’t be found until the theory starts to be taken seriously as a real possibility. It may take different people to provide the new evidence it needs or even to imagine a crucial piece of evidence only later to be realised. That’s the kind of thing I’d say to John on this. But in fact you’d also have to explain the nature of evidence to many people, who wouldn’t dare start the process of familiarising a new theory until the alternatives had already been completely blown out of the water… by which time their assistance in fostering the new idea would be valueless, along with their opinion of course.

One problem with the slogan is its famous support by Carl Sagan. He more than most should have realised the damage it does to the “potentially promising but not favoured until more evidence analysed” status of so many theories, since he actually has supported many new and originally unfavoured theories later vindicated. I take his involvement with that list as putting him in the excellent scientist class; if that also put such people in the excellent philosopher of science class, my blog would not be necessary. (Sagan’s first wife was Lynn Margulis who died last week (November 22, 2011), famed, as Wikipedia says, “for her theory on the origin of eukaryotic organelles, and her contributions to the endosymbiotic theory”. You can take it that she will have needed to spend ten times the effort getting the theory past the blockheads opposing it as she did formulating her theory in the first place. And if that disastrous slogan Carl so pointlessly promulgated hadn’t been so much in their minds, explicitly or implicitly, she wouldn’t have needed to.)

Before Sagan, sociologist and early influencer of the skeptical movements Marcello Truzzi boosted the slogan, and others just as damaging if not more so. This disastrous sentence of his combines two: “In science, the burden of proof falls upon the claimant; and the more extraordinary a claim, the heavier is the burden of proof demanded” (from Wikipedia). We’ve just dealt with an absolute version of the latter; Truzzi’s version with “more” and “heavier” denies the commonplace transfer of balance between vastly differing theories by tiny pieces of new evidence. The talk of proof at the start of the quote is unforgivable; he should have known rejecting a null hypothesis at say the 95% confidence level, which sources so much scientific ‘knowledge’, abrogates proof. And the argument that no amount of evidence can ever prove a theory has been reiterated more often that I care to remember. There is no essential role for distinguishing between agents presenting evidence (unless the agents’ characteristics are being taken into account). Who presents evidence or argument is irrelevant. In fact, any scientist noticing the new theory (and all should keep their eyes open) are obliged to take it and other theories fairly into account, and indeed propagate their existence, or else keep out of the argument.

Prior to Truzzi, Laplace said: “The weight of evidence for an extraordinary claim must be proportioned to its strangeness.” Untrue; theories must be evaluated according to what they predict etc., irrespective of their “strangeness”. Laplace’s advice also tends to encourage the error of accepting an only slightly new theory without due diligence. Mathematicians, even top ones, too rarely follow or advise principles suitable for the natural sciences. Prior to this, David Hume said “A wise man, therefore, proportions his belief to the evidence”(wiki) but by today’s standards that’s not very profound or even useful, and in any case “Extraordinary claims require extraordinary evidence” doesn’t inevitably follow from it.

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