Thursday, April 13, 2006

Catfish and Creationism

It was reported in the New York Times today that scientists in the arctic found a fossil of a 375 million year-old fish able to walk on limbs. It is being cited as a possible connection between ancient sea dwelling animals and tetrapods, the earliest land-dwellers. Filling in this missing part of the puzzle will generate plenty of work for evolutionary biologists.

And, of course, every boon to evolutionary biologists requires the usual political nonsense. From the Times article,

Dr. Shubin's team played down the fossil's significance in the raging debate over Darwinian theory, which is opposed mainly by some conservative Christians in this country, but other scientists were not so reticent. They said this should undercut the argument that there is no evidence in the fossil record of one kind of creature becoming another kind.
First of all there is no "raging debate over Darwinian theory." As if (1) this evidence was really that crucial to making a reasonable case for speciation, (2) the opponents will treat it honestly. But it does warrant some thought about how and why it undercuts the creationist or intelligent design argument.

The usual line that you see so frequently is that creationists or ID folks are putting together a purely eliminavist case. They do nothing but try to poke holes in evolution and then assert that this shows that their preferred alternative must therefore be true. But this alternative is not scientific, the line goes, because, following Karl Popper, it is not falsifiable and all scientific propositions are falsifiable. These discoveries serve to not only undermine the negative arguments of the anti-Darwin crowd, but highlight the unfalsifiability of their own view.

The problem is that Popper's view is wrong. Even the best scientific theories have parts that are unfalsifiable. Take Newton's first law that anything in motion with no net external force applied to it will move in a straight line at uniform speed. This is unfalsifiable -- there are no objects subject to no net external forces. This is not true of anything and yet is a founding principle of the theory.

One claim is that there theory as a whole is falsifiable. But when counter-examples are found, we do not -- as Popper requires -- consider the theory refuted, rather we make changes to parts of the theory but do not touch other parts. This was exactly what happened when the planet Neptune was discovered. The orbit of Uranus was not as predicted,so instead of throwing out Newton's theory, we changed another assumption, that there were seven planets. Real scientists, doing real science, refused to allow parts of the real sceintific theory to be falsified.

This was all pointed out by Popper's student Imre Lakatos. Lakatos argued that parts of every scientific theory are considered unfalsifiable. This hard core would never be messed with, but was surrounded by a protective belt of other assertions. This belt could be adjusted as needed to save the hard core. There are unfalsifiable parts of evolutionary theory, just as there are in ID. Indeed, the work of some of the more clever ID folks seems to show that in information theory and other branches, there may be something that is at least indirectly falsifiable about intelligent design. If some versions of creationism and intelligent design are indeed unfalsifiable, it doesn't mean that every such version is necessarily, in princple, so.

But we can, according to Lakatos, tell better from worse theories. Better theories are ones that need less adjustment or whose adjustments make it more testable -- that is, open to more cases where it might make wrong predictions. These theories are progressive. Worse theories are ones that need more frequent adjustment and whose adjustments make them less testable. These theories are degenerate.

This is what we see with each new fossil. It takes evolutionary theory makes a big progressive leap and the non-evolutionary theories need to adjust their protective belts in a way that makes them degenerate. There is reason to think that each one of these new discoveries does support evolution over its theologically inspired competitors, but it is not because of falsifiability as we often see claimed.