Tuesday, January 24, 2006



I've neglected this blog for more than a year because I was busy posting at the Access Research Network, a hotbed of “intelligent design”. I stopped posting there because I got fed up with the same old tired arguments. (To be sure, though, they got fed up with my tired arguments.)
I learned a lot, though. There are a number of actual scientists there, who make good arguments based on good science. There are also a number of people who are advance vociferous arguments that range from misguided to bizarre. I think of some of these as “conceptual whetstones”: dense and abrasive, but useful for sharpening. In trying to counter some of these misconceptions, I've gotten a deeper appreciation for some of the basic ideas of evolution. Nobody over there seems about to change their minds, so I decided to leave, and get back to my own blog.

This post was inspired by one of my antagonists claiming that I had confused cause and effect . Because causality is an interesting and subtle concept, I'm starting out with that topic. I had pointed out changes in a popoulation are caused by variation followed by natural selection, which prompted him to say that “a 'variation' is an effect, not a cause.

Discussion of causaliy goes back at least to Aristotle, who identified four Causes. These are usually given as Material Cause (the stuff of which a thing is made), Efficient Cause (the process by which it is made), Formal Cause (the shape into which it is made), and Final Cause (the purpose for which it is made). The traditional example is a statue: the Material Cause is the marble; the Efficient Cause is the action of the sculptor; the Formal Cause is the shape of the statue; the Final Cause is the desire to have a statue.

Marc Cohen, of the University of Washington at Seattle, gives a more nuanced view: The word we translate as “cause” is better rendered as “explanatory factor”. Aristotle's example of Final Cause is “Why is the man walking around?” “For his health”. The Final Cause of the statue may be that the sculptor needed money.
Efficient Cause can be elaborated:
  • The Efficient Cause of the statue is the wedging of the blade of the chisel into the crystal structure of the marble.

  • The Efficient Cause of the moving chisel is the motion of the sculptor's hand.

  • The Efficient Cause of the motion of the hand is the contraction of the arm muscles.

  • The Efficient Cause of the muscle contraction is electrical impulses from motor nerves.

  • The Efficient Cause of the electrical impulses is thought patterns in the sculptor's brain.
Some considerations:
This last step sort of merges Efficient Cause with Formal Cause.
The electrical impulses are filtered through synapses, which reflect the sculptor's practice
with chisel and marble.
The muscle contraction involves several mechanisms that I left out.

The Scottish philosopher David Hume changed people's notions of causation:
Hume sums up all of the relevant impressions in not one but two definitions of cause. The relation -- or the lack of it -- between these definitions has been a matter of considerable controversy. If we follow his account of definition, however, the first definition, which defines a cause as "an object, followed by another, and where all objects similar to the first are followed by objects similar to the second", accounts for all the external impressions involved in the case. His second definition, which defines a cause as "an object followed by another, and whose appearance always conveys the thought to that other" captures the internal sensation -- the feeling of determination -- involved. Both are definitions, by Hume's account, but the "just definition" of cause he claims to provide is expressed only by the conjunction of the two: only together do the definitions capture all the relevant impressions involved.
We have to be careful here, though. It might be that the two objects have a common cause, rather than one being the cause of the other. (We might have to use a different definition of “cause” in order to make this work.)

In 1948, the German philosopher Carl Hempel presented his “covering law” model of causation, which starts with one or more natural laws, then derives causation from law and conditions. (But how do you discover natural laws before you have an idea of causation?)

This is still not final, though. Some philosophers are broadening the idea of causation to go back to some of Aristotle's ideas. If someone asks “Why is the porch light on?”, a natural-law answer like “Because electric current is flowing through the filament” would be considered either non-responsive or smart-alecky. An acceptable answer might have the form “Because I am expecting company”, or “Because I forgot to turn it off”. “Expecting company” is a Final Cause; forgetting assumes that there was a reason for turning it on in the first place.

All of this is incomplete; what I want to do is come to a brief discussion of causation in biology. Consider one of the steps in the evolution of the jaw. An embryo of a vertebrate has a number of arches in the pharynx. In a lamprey, a jawless fish similar to an eel, the first arch develops into the lips of the mouth. In a jawed fish, one of the growth factors is expressed at a slightly different place, with the result that the arches grow into jaws. Biologists have been saying for decades that pharyngeal arches evolved into jaws, and creationists denied it. This is direct evidence of how it happens.

But why does this shift happen? Is this a cause or an effect? Going back to the Efficient Cause of the statue, it seems that this is both an effect and a cause, that is, it is a link in a chain of causes. The mechanisms of controlling gene expression are known in general terms; I suspect that somebody is trying to figure out specifics for this pathway.

What about Material Cause? In the case of the statue, the marble is completely passive; the chisel does all the work. The creation of the statue would be much the same if the material were wood or clay. The situation is much different in biology. Here the shapes of the molecules control what happens. The Efficient Cause is the chemical attraction between molecules. Two hydrogen atoms and an oxygen, at a high enough temperature (which is the same as kinetic energy), will form a water molecule. When one or more molecules interact with an enzyme, the shape of the enzyme interacts with the shape of the molecules in order to bring about the chemical reaction.
So in sculpture, the Material Cause is largely irrelevant; Efficient Cause is (almost) everything. The tools might vary somewhat, and the fine motions of the hand will be different, but for a sculptor experienced in several media, there is little difference. In biology, by contrast, Material Cause is everything, while Efficient Cause makes no difference.

Formal Cause in biology might be treated as an example of emergence.

I suggest that the difference in Material Cause and Formal Cause is what marginalizes the analogies with watches and automobiles that the creationists and their “intelligent design” brothers like so much. Watches and cars are like the statue: Material Cause is irrelevant. Clocks used to be made of wood. You can make a car out of plastic as well as steel. It will perform differently, but the assembly process is much the same. A biological entity constructs itself, based on the shapes of the constituents.

FOLLOWUP: While this post was fermenting in my Drafts section, this post at the Philosophy of Biology blog discusses another aspect of Aristotle's philospophy. Be sure to read the comments.