When Newton's much vaunted theory of gravity was complete, it was celebrated as the best explanation for the motion of physical objects in the solar system, from rocks falling on the earth, to the motion of the moon, to the elliptical orbit of Mars about the sun. But the orbit of Saturn did not match the prediction of Newton's theory. It occasionally departed from the nice ellipse it was supposed to trace out, as it orbited the sun. This departure from the prediction of a reliable theory is a classic example of an anomaly.
Saturn's anomalous path suggested that there was something wrong with Newton's theory, to be sure. And astronomers at the time worried about that. But the Saturnian anomaly suggested only that Newton's theory might not be a perfect explanation for everything; it did not suggest in any way that Newton's theory was not the best explanation for most things. And the resolution of this famous anomaly was, of course, the discovery of the planet Uranus, which tugged on Saturn every time they passed each other, giving it the puzzling wobble they were worried about. When the influence of Uranus was considered, the anomaly plaguing Newton's theory disappeared.
Anomalies typically work like this in every scientific theory; they are small puzzles inviting scrutiny, and almost never pointers to some wholesale replacement theory. And anomalies typically get resolved, as was the case with Saturn, within the larger framework of the very theory that they once appeared to contradict.
I wonder if Bill may have absorbed a widespread misunderstanding about anomalies from the anti-evolutionary community of which he is a leader. This misunderstanding is rooted in two closely related fallacies: the "lawyer" fallacy, and the false dichotomy. Fallacies, as we study them in Logic, are not just mistakes in reasoning. They are particularly seductive mistakes in reasoning that are easy to miss. The false dichotomy emerges when we mistakenly assume that there are only two options on the table. If there really are just two options available to us then evidence against one actually serves as evidence for the other. This is why negative campaigning in the United States is so effective. A politician can get elected with an argument that amounts to nothing more than "The other guy is terrible!"
The anti-evolutionary community has long framed the origins conversation as a false dichotomy: we have to choose between godless evolution or creation/intelligent design. If this really is the choice, then an anomaly that undermines evolution could be interpreted as pointing in the direction of intelligent design. But without the fallacious assumption of the dichotomy the anomaly says nothing in particular. It simply calls attention to itself, like Paris Hilton.
The "lawyer" fallacy is a variation on the false dichotomy and has long been a part of the anti-evolutionary movement. Phillip Johnson's Darwin on Trial, published in 1991, was remarkably similar to Norman MacBeth's Darwin Retried, published two decades earlier. Lawyers, at least the ones we watch on TV, live in a world that is artificially black and white. They stand astride a dichotomy of "guilty beyond a reasonable doubt versus innocent." The task of the defense lawyer is to provide "anomalies" that will provide the jury with reasonable doubts about the prosecution's "theory." The defense lawyer is not required to provide a replacement theory. He can be entirely successful by simply destroying the best theory and leaving the prosecution with nothing to replace it.
Science does not work like this. If anomalies in science worked like they do in jurisprudence, there would be no scientific theories of any sort. Virtually all scientific theories have anomalies and, when they are being born, they arise slowly from under a gigantic pile of anomalies, like a rescue worker climbing out of the rubble of a collapsed building.
Bill and I have dramatically different perspectives on the significance of anomalies. I think anomalies in science are far too subtle to be lifted out of their context and evaluated as stand-alone bits of evidence. Bill writes, for example, "The issue is not who's doubting Darwinism, but what are the arguments for and against it and whether they have merit." I completely disagree with this statement. A scientific theory could have ten major evidences in its favor and two anomalies contradicting it. To adjudicate such an example is complicated. Not all evidence is equal and it requires deep experience and wisdom to make the appropriate evaluation.
In the case of Newton's theory, the orbit of the moon provided solid evidence for the theory and the orbit of Saturn provided evidence against it. But, as the astronomers at the time saw clearly, the evidence from the moon deserved to be weighted more heavily—it deserved, in some sense, more votes. If 17th-century "antigravitationists"—the French astronomers desperately hoping René Descartes would win the international competition for most brilliant scientist—had demanded that people either explain the Saturnian anomaly or reject Newton's theory, they would be much like the anti-evolutionists of today. This is why I think history of science is so important in these discussions; we have seen all these arguments before and should be cautious when long dead arguments arise from their crypts and sneak back into the discussion.
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