Tuesday, 15 April 2014
Noah the undertaker
For a hypothesis to be scientific and not simply a just-so story, it must meet certain criteria. Among these is falsifiability, or the possibility to be proven wrong. If an untestable hypothesis cannot be proven wrong, that doesn't make it right: it makes it useless. So the next time uncle Arthur tells you that you cannot prove that Leprechauns don't exist and that they're the reason thousands of unidentified people disappear each year, don't fret about it: the burden of the proof is on him, not on you.
Of course, in the case of a hypothesis that could be proven wrong but isn't, the lack of negative evidence (especially as the hypothesis or theory is tested again and again) makes one more and more confident that it is right.
A famous quote about the falsifiability of the theory of evolution is attributed to the famous biologist J.B.S. Haldane. Asked about what could convince him that the theory was wrong, Haldane answered "rabbits in the Precambrian". As we've mentioned before, the succeeding geological eras of our planet left layers of sedimentary rocks piled one over the other under our feet; these layers allow us to get a glimpse of what life looked like as we go farther and farther back in time (or deeper and deeper in the ground, which amounts to the same thing). An obvious testable prediction is that according to that theory, one should not encounter the remains of a life form in a layer that predates its apparition. During the Precambrian (anything older than 541 000 000 years BCE), we were still millions of years from the appearance of the first primitive fish, let alone amphibians, let alone reptiles, let alone mammal-like reptiles, let alone mammals, let alone rabbits. Were we to find fossilized rabbits among the remains of the Ediacara biota, it would fit with the theory like a square peg in a round hole. So there are ways to prove this theory wrong, and the fact that we can't is a pretty strong endorsement for its validity.
Needless to say, there aren't any rabbits in the Precambrian strata. That leaves creationists with a bit of a problem: how did fossils get organized in a way that somehow agrees with the theory of evolution? Hypotheses vary. Some claim that an evil imp organized fossils that way to confuse people. Some argue that as Noah's Flood struck, slower-moving animals like dinosaurs were drowned first and were the first to be buried under sediments. This is actually not an untestable hypothesis, unlike the first one, but it doesn't hold water (pun unintended). For one, the deeper strata do not contain the remains of dinosaurs, which appeared hundreds of millions of years after the Precambrian: they contain the remains of marine animals (no dinosaurs, no rabbits). Second, a large number of dinosaurs were not particularly slow-moving, judging from what biomechanics tell us about their skeletons. Third, according to this hypothesis, all slow-moving animals should be found in a deeper stratum than fast-moving ones; and yet, sloths are found just where the theory of evolution expects them: with other mammals, fast and slow, not with dinosaurs.