Thursday, November 02, 2006

Darwin and Design

1) I read a lot of Kant in high school, when I was an atheist. I'm not sure what I think about his thought generally now, but one thing in it can be certainly accepted: that the understanding which animates science seeks unity above all. Kant had his little table of the different ways in which unity is sought, but the big daddy of them all is cause and effect: the aim of science is to link all the events of the world in a branching and expanding cause and effect chain. (In Kant this has all kinds of implications about the status of cause and effect, the first cause, and so on, but let that slide.) In the long run, a theory that brings lots of isolated facts together exemplifies the scientific understanding more than one that leaves them isolated. Total common ancestry is one such a theory for biology, and like the unified theory in physics it will stand as either proven or else be seen as the single great desideratum of the field.

2) In one sense any guidance in evolution makes phylogeny (the science of constructing family trees of living and fossil creatures) impossible to do. Look at it this way: fossils don't come with little labels saying (for example): "Mesohippus, ancestor of Equus, and descendant of Eohippus." In theory, any fossil type could be the ancestor of any later one, and the descendant of any previous one. Unless you want all the thousands upon thousands of (for example) more or less horse-like skulls to just sit in their cabinets as unconnected species, you have to conjecture relationship, and to make the conjecture workable, you have to find some parsimonious way of excluding the alternatives. Natural selection, Darwinism, whatever, does that, but only as long as it is unguided. Natural selection tells you not only that all changes must be relatively small (relative here is the word, and people often talk past each other in terms of scales on this point), but also that every change must be plausibly explainable in terms of some immediate advantage. That immediately constrains the possibilities. This is the condition of any hope of sorting the thousands upon millions of fossils into anything like orderly family trees (phylogeny).

An analogy: let's say I showed you a bumpy slope, and gave you the complete topography. Let's say I then showed you three points and said water had been flowing past that point, and then told you that all three points were part of one stream. Could you reconstruct the course of the stream? Maybe, but only if you are assured that water can't flow uphill. The second you admit water can flow uphill, the course of the stream becomes unreconstructable. Ditto. for phylogeny. For a phylogenist, admitting that anything other immediate survival advantage causes changes from one species/type to another is the same as giving up.