Sunday, February 27, 2005


Beyond Ockham's Razor

This essay began as a comment to a post on the Philosophy of Biology blog. The post reproduces the New York Times article by Michael Behe. My first comment was

"The fourth claim in the design argument is also controversial: in the absence of any convincing non-design explanation, we are justified in thinking that real intelligent design was involved in life."

This is an epistemological claim with an ontological implication. If we conclude that life is intelligently designed, it would seem to follow that there is/was some sort of entity doing something to move DNA molecules into positions that they had not occupied before the design was accomplished. Ockham's Razor, however, requires that we choose the alternative requiring the fewest ontological assumptions. (This is not exactly a formal requirement, but it seems like a damn fine idea.) Mainstream biology gets its ontology from observation and experiment; until ID can do something similar, we can't assume an entity out of pure logic.

A note on spelling here. William was born in the English village of Ockham, Surrey. The name of his village is often given the Latin spelling "Occam". Being a bit of a pedant, I prefer the original.

Someone replied

It's not even close to a formal requirement. Simplicity is an aesthetic criterion and should be judged accordingly. Some have a taste of "desert landscapes" and some do not.
I was absent from the fray for a couple of days, during which more comments were made. The commenters agreed that Copernicus's theory of the planets was simpler than Ptolemy's.

When I returned, I commented (slightly modified):

Ockham's Razor is not about simplicity, it is about parsimony. Latin versions of the original vary somewhat between sources, but the essence of the translation is that "Plurality should not be posited without necessity". The comment asks in effect "What does 'necessity' mean?"

These are the sorts of questions that are asked by physicists. "Do we need a fifth force, or are the traditional four sufficient?" (The answer seems to be that four are enough.) Biology takes a crisper view: The preferred explanatory principles are those that can be observed, and, preferably, experimented with outside the present experiment. As an example: In the early 20th century biologists developed the concept of the "morphogenetic field", in order to explain the development of organismic form. With the rise of genetics, the morphogenetic field fell out of favor as an explanation. In the last few decades, though, the field has made something of a comeback, now taking the form of a gradient of some signaling protein.

There is a significant ontological difference between the two concepts. Nothing much can be said about the morphogenetic field, except that there is purportedly no other way to account for form. On the other hand, the level of a protein can be measured, and the speed of diffusion calculated. The protein was discovered before it was used in the field concept; it can be analyzed in isolation. The diffusion can be manipulated, by adding protein, or by adding an antagonist. The morphogenetic field has thus become a mechanical concept, although not by that name.

Nothing of this sort can be said about any kind of designer. The only formal reason IDists can give for talking about a designer is that they feel lost without it. Biologists are more adventurous, and more resourceful.

And, incidentally, Copernicus's theory was not all that much simpler or more parsimoneous than Ptolemy's. By putting the sun in the center of the universe (partly for philosophical reaons), Copernicus was able to eliminate one layer of epicycles. He still needed them though, because he still based his system on Aristotle's idea of circular orbits.

Kepler's use of Brahe's more-precise planetary positions led him to the concept of elliptical orbits. It is one of the ironies of history that Galileo, the die-hard champion of Copernicus, never accepted ellipses, because he was not willing to go that far in contradicting Aristotle. Ellipses could be dismissed as a mathematical device, which they pretty much were. They became theoretically real only after Newton showed that his inverse-square gravitation predicts elliptical orbits. But Galileo had made his stand on the physical reality of Copernicus's theory; the Church would probably have been content if he had accepted that it was mathemetical only. So we might even consider him justified in rejecting ellipses.

In the end it comes down to what you want from a theory. If you want esthetic satisfaction, then maybe ID is for you. All you really have, though, is a morphogenetic field, something that answers only one question, and you can't even say why it answers it. If you want a description of reality, you have to buiid it one brick at a time.

And very, very few biologists put any credence in Behe's claim that they have hit a brick wall.

I'd like to go beyond what I said before. PZ Myers's article on the evolution of the jaw is an example of what argument in biology is coming to look like.

Carl Zimmer has an article about theories of the origin of language.

More about both of these next time.


Post a Comment

<< Home