Wednesday, January 20, 2010

Top-Down Causation (Part 3): Some Problem Cases

This post is part of my series on the work of the philosopher Carl Craver. The series deals with the nature of neuroscientific explanations. For an index, see here.

I am currently looking at an article written by Craver and William Bechtel entitled "Top-down Causation without Top-down Causes".

In Part One, I detailed how mechanisms occur in nested hierarchies. In Part Two, I showed how this can seem to allow for interlevel causation (i.e. between different levels of mechanisms). I also covered how some popular ideas about causation do not seem to allow for interlevel causation. Finally, I sketched Craver and Bechtel's solution to the problem.

They argue that what is referred to as interlevel causation arises from the constitutive relationship between a mechanism and its parts (including sub-mechanisms). A mechanism is a spatiotemporal organisation of parts. So a change in the parts constitutes a change in the mechanism. And likewise, a change in the mechanism as whole constitutes a change in its parts.

The Craver-Bechtel solution allows for standard interpretations of causation to apply intra-level.

This part covers the application of the Craver-Bechtel solution to some supposed cases of bottom-up and top-down causation.

1. Bottom-Up Causation?
Suppose you are infected by a virus of some kind. Suppose further that the virus kills you. Is this a case of bottom-up causation? The affirmative answer arises from a belief that viruses and humans exist at different "levels".

Craver and Bechtel think the affirmative answer results from a misunderstanding of what a "level" is. There is nothing about the structure of mechanisms that prevents small things (like viruses) having an effect on a big thing (like a human). For example, I can swat and kill a fly; a spark can ignite a fuel tank; and molecule can exert a gravitational force on a planet. There is nothing problematic about inter-size causation.

A second case might pose more of a problem. Take someone who dies of a heart attack. The heart is very definitely a sub-mechanism within the human body. Is it thus wrong to speak of a heart attack causing someone's death?

Well, if someone dies of a heart attack, it is because the oxygen supply to their brain and other bodily organs is cut-off. This results in the shut-down of all the mechanisms that constitute the human body. We can trace the breakdown of individual sub-mechanisms to intralevel causes and we can trace the breakdown of the overall mechanism to the constitutive relations.

Indeed, the heart attack scenario provides a great illustration of the Craver-Bechtel approach to causation.

2. Top-down Causation?
Let's take a look at Roger Federer. An effortlessly elegant tennis player if ever there was one. However, even Federer, when he starts playing tennis places his body under stress. He needs to metabolise glucose to keep going. This involves blood-borne glucose being taken-up through the cell membrane, then being phosphorylated and being bound to molecules of hexosediphosphate.

The question is whether the tennis-playing causes the increase of glucose metabolism. If it did, this would make tennis-playing a classic instance of top-down causation.

Craver and Bechtel argue that the glucose metabolisation can be given a complete explanation by using their mechanistic model. First, when Federer starts to play, nerve signals are sent from the brain to the muscles. This causes the muscles to metabolise available ATP to ADP, which results in muscle contraction. The increased levels of ADP make that molecule available as a receptor for phosphate in high energy bonds at the end of the glycolytic process. This allows a cascade of reactions earlier in the glycolytic pathway to proceed, part of which involves the glucose reaction described earlier.

This is an incomplete sketch because a full description of the series of biochemical reactions would be incredibly long-winded. The main point is that there is a mechanistic story to be told all the way down and up.

Craver and Bechtel offer another useful example of this drawn from the movie Citizen Kane. However, it deals with memory mechanisms. I will be discussing these in later posts and so will avoid repetition here.


  1. You need a Table of Contents page for this site, like mine. One that you keep updated.

  2. This comment has been removed by the author.

  3. Is there a way of doing such a thing without it being simply a label on one post? I'm not too good on page design, I'm relying on what comes loaded with blogger.