But the Enlightenment turned that idea on its head. The idea was the scientific method that started with observation rather than inspiration, and built up a pyramid of understanding. First, by the process of induction, many observations were made, seen to be consistent, and they lay at the base of knowledge (All the swans I've ever seen are white, therefore all swans are white). Other types of generalization built upon this base, to the top of a pyramid of understanding, the final theory that we infer from facts.
When Darwin published his theory of evolution, of descent with modification screened by natural selection, from a common ancestral form, it was a challenge to accepted wisdom. The scientific method was well established, but religious explanations of life were rife. Darwin's theory certainly challenged this big-time!
Now, Darwin amassed countless facts--it was one of his incredible fortes. From these he inferred his theory, and on the face of it this would seem to be the scientific method if anything was. But the geologist and former friend and teacher of Darwin's, Adam Sedgwick, was rather incensed by the theory of evolution. Sedgwick was a seriously Christian believer, and could not abide this threat to all that he held dear. He lambasted Darwin, not explicitly because Darwin contradicted biblical explanations, but because Darwin's theory was (in our words) Aristotelian rather than Baconian: it was incorrect, old-fashioned and not real science at all!
|Inverted pyramid, the Louvre|
In various discussions of this topic then and since, it appears that Darwin largely conceded the formal point, but of course stuck to his guns. He could (and we can) predict new facts, but they are details that can immediately be fitted (or, Sedgwick would perhaps argue, be retro-fitted) into the theory. Yes, there was diversity in the world, but this could arise by other processes (such as special Creation) and the theory of evolution was not the only explanation as a result. It was not, argued Sedgwick, properly inductive.
One could argue that we have used this theory in so many ways, modeled mathematically and experimentally in artificial selection, to predict formerly unknown phenomena about life, that the theory has clearly stood the test of time. Many facts about the one process on earth, could be used to generalize about the process as if it could be repeated. We argue that different species in different places each do represent replicate observations from which the process of evolution can be induced. Or, one could argue, inductive reasoning is just one way of getting at convincing accounts of the nature of Nature.
One might even go all the way with Aristotle, and say that for the very reason that evolution did occur, our brains were adapted (by Darwinian processes!) so that we are built to understand Nature! The argument probably wouldn't hold much water, but it's a thought. In any case, the fact that evolution only occurred once does suggest that the idea was cooked up by Darwin in a non-inductive way--even if his theory was built upon countless observations, but of one single process.
The triumph of the Darwinian method, to use the title of a book by Michael Ghiselin that we posted on in October and November 2011, proliferates throughout the life sciences. There are things that this allows us to do that are not exactly inductive, but are close to inductive reasoning in many ways. This has to do with the nature of variation and how it's to be explained. In a next post we'll discuss this in light of DNA, totally unknown to Darwin. There are substantial problems, and many of the inferences we make about specifics of the past are speculative, but overall, Darwin was not a Madoff, and did not hustle us with a pyramid scheme!
We'll see how Darwinian concepts, more than any other, enable us to understand why DNA sequence can be 'random' on its own, in the sense that the A,C,G,T's along DNA are by various statistical tests random: the nucleotides in one place don't predict those nearby or elsewhere along the sequence. Yet the nucleotides are not just letters in a computer test, and are in fact anything but random. Indeed, the concept of randomness has to be revised because DNA sequences evolved.