Susanna Cornett over at Cut on the Bias decided, one fine day, to pick a fight with the evolutionists. (Gene Expression replies in detail; Susanna rebuts, in somewhat less detail.) Her jumping-off point was the recent discovery of a couple of hominid skulls that don’t fit the current view of human evolution. A paleontologist says, “This really exposes how little we know of human evolution and the origin of our genus Homo.” Susanna writes triumphantly: “But wait! I thought we knew all that! It’s been taught for years as immutable truth.”
Not exactly. Virtually all biologists agree that natural selection is true; but they ardently disagree about the mechanism and the path. An analogy from the history of calculus might be helpful. When Newton and Leibniz discovered calculus they based it, theoretically, on infinitesimals, quantities that are arbitrarily small, but not zero. Bishop Berkeley pointed out, correctly, that the concept of an “infinitesimal” is logically incoherent. It wasn’t until the end of the 19th century that Weierstrass put calculus on a proper foundation by defining limits rigorously. But that didn’t stop people from using calculus in the meantime: it worked, it solved problems that no other method could solve as quickly, or at all. Same with natural selection. It solves too many problems to be thrown over every time some new morphological evidence shows up that’s difficult to classify.
Susanna continues: “Ive been taught, as a social scientist, that you look at behavior, or evidence of various sorts, and ponder about it until you come up with an explanation. Then you devise a test to see if your explanation fits.” I doubt whether this is true even of the social sciences — von Mises and the Austrian economists, for example, argued that economics was deductive — but physical science assuredly does not work this way. It was not pondering the facts that brought Copernicus to advocate heliocentricity. Copernicus’s model, before Kepler, actually fit the facts worse than the Ptolemaic model. But it ditched all the secondary and tertiary epicycles. It was simpler. I don’t know exactly how Descartes arrived at the central insight of mechanics, that a body in motion remains in motion unless acted on by an external force; but it was not by “looking at behavior.” Aristotle, on the other hand, watched horses pull carts, and concluded that constant velocity requires a constant force, which is plausible, intuitive, and false.
But if Susanna likes tests, I propose that she devise one for the validity of intelligent design. What evidence would persuade her that intelligent design is false? I won’t presume to answer for her, but if I advocated intelligent design, my answer, I think the only consistent answer, would be, “No evidence.” For nothing, in principle, is incompatible with the miraculous. And a theory that can accommodate any evidence is not a scientific theory.
(Update: Susanna points out that she has a further post on the subject and accuses me — but very nicely! — of “piling on.” It might look that way, although I hadn’t read the Charles Murtaugh post on which I was supposed to be piling, and I certainly griped about the testability of ID and the all-inclusiveness of God theories, just as Razib did. But the bit about forming scientific hypotheses — that was mine, all mine, dammit!)