Did Darwin run a pyramid scheme? Darwinian method, continued

Before the period of the Enlightenment in science, roughly starting with Francis Bacon and Galileo and others, about 400 years ago, a model of knowledge (among scientific types, at least, not farmers and craftsmen and others who actually earn a living) was largely attributed to Aristotle from around 400 BC.  According to this view of how we should figure out the world, we were hard-wired to understand the nature of Nature (sounds like a lot of genetic or Darwinian determinists, doesn't it?).  Thus, knowledge could be deductive (the classic example of this is 1) All men are mortal, 2) Socrates is a man, 3) Therefore, Socrates is mortal).  The basic truths were known and were in that sense axioms from which predictions about facts to be found could be deduced.  In a sense, the facts were latent in the assumptions.  A theory came first, and led to many facts.  (The BBC Radio 4 program, In Our Time, featured a nice discussion of the Scientific Method last week.)

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

Sedgwick basically argued that Darwin inverted the proper pyramid of knowledge.  He claimed to be using inductive reasoning by bringing to bear so many different facts to form a consistent theory.  But in fact, argued Sedgwick, this was not induction at all!  That's because Darwin used the outcome of life that he observed as if he could draw conclusions from it inductively, when in fact life had only progressed on the Earth once!  Thus, Darwin was taking a single observation, partitioned into many minute facts to be sure, but was generalizing about life as if evolution were observed again and again.  This, said Sedgwick, was old fashioned a priori theory driven reasoning that Aristotle would be proud of, but it did not have the empirical truth-value that the scientific method was developed to provide.

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.