[Note: updated 04/08/07 with examples from Carl Craver's paper.]
I just culled together a bunch of putative examples of downward causation, some from advocates, some from detractors. Particularly interesting and promising is the article by Robert Bishop, Downward causation in fluid convection, and Bechtel/Craver’s article Top-down causation without top-down causes, for which brief quotes will not do justice. (Note Craver contributes on this forum: nice paper Carl!) I thought it would be helpful to have these examples here to gnaw on. Most people think top-down causation is just poppycock, but perhaps some of these examples (and especially Bishop’s paper) will help reveal that there is an extension to the term ‘downward causation’, even if the term is ill-chosen. Frankly, I am not sure what I think.
Let me illustrate this with an example. It is well-known that snow
crystals have a strict 6-fold symmetry, but at the same time that each
crystal has a unique symmetric shape. The symmetry of the crystal
(whole) is clearly determined by the physico-chemical properties of the
water molecules which constitute it. But on the other hand, the shape
of the complete crystal is not determined by the molecules. Once a
shape has been formed, though, the molecules in the crystal are
constrained: they can only be present at particular places allowed in
the symmetric crystalline shape. The whole (crystal) constrains or
“causes” the positions of the parts (molecules).
Certainly, there seems to be no shortage of examples of downward causation. Certain psychological states (e.g., prolonged anxiety, embarrassment) can cause physiological effects (heightened blood pressure, eczema, blushing) in a human body. McClelland’s experimental studies of human motivation showed that affiliative motives (the capacity to love and be loved) promote better health. For example, the salivary immunoglobulin A levels of subjects were significantly increased when they view a film of Mother Teresa designed to arouse affiliative motives.30 Again, the functional molecules (DNA, proteins, fatty acids, etc.) within a cell are fabricated within internal processes of the cell itself; they are generated through the web of interactions of the whole system. That downward causation occurs is a fact; how to understand the phenomenon is the contentious issue.
From Roger Sperry at http://www.noetic.org/publications/review/issue04/r04_Sperry.html:
As such an illustration, consider a molecule in an airplane leaving Los
Angeles for New York. Our molecule, say in the water tank or anywhere
in the structure, may be jostled or held by its neighbors—but, these
lower level actions are relatively trivial compared to the movement
across the country. If one is plotting the space-time trajectory of the
given molecule, those features governed from above by the higher
properties of the plane as a whole make those governed at the lower
molecular level insignificant by comparison.
The same principle applies throughout nature at all levels. The atoms
and molecules of our biosphere, for example, are moved around, not so
much by atomic and molecular forces as by the higher forces of the
varied organisms and other entities in which they are embedded. The
atomic, molecular and other micro forces are continuously active but at
the same time they are enveloped, submerged, superseded, “hauled and
pushed around” by, or ‘supervened” by an infinite variety of other
higher molar properties of the systems and entities in which the micro
elements are embedded—without interfering with the physico-chemical
activity of lower levels.
Someone else discussing a different Sperry example, one from the 1960s (found at http://www.nbi.dk/~emmeche/coPubl/2000d.le3DC.v4b.html):
One of the central examples given by Sperry (1969) is quite simple: a
wheel running downhill. None of the single molecules constituting the
wheel or gravity’s pull on them are sufficient to explain the rolling
movement. To explain this one must recur to the higher level at which
the form of the wheel becomes conceivable.
Just one little snippet from the Bishop paper, where he uses the example of fluid convection patterns as a nice case study. This is one example where I’m not sure the Bechtel/Craver framework will work (I’m not sure it won’t either). Again, this paper is at http://philsci-archive.pitt.edu/archive/00002933/01/Downward.pdf :
Worries about [causal closure] normally arise in the context of philosophy of mind, but in the context of Rayleigh-Bénard convection, higher-level physical structures (Bénard cells) constrain and modify the behaviors of the lower-level system constituents (fluid elements).
And two nice examples from the Craver/Bechtel paper (I left these out by accident in my original post), which can be found at http://philosophyfaculty.ucsd.edu/faculty/pschurchland/classes/cs200/topdown.pdf:
Ignatius, with much labor and strain to his valve, coaxed his hotdog cart to the corner. The cart was full of hotdogs. What caused the hotdogs (and the molecules in the hotdogs, and the atoms comprising the molecules, and so on) to arrive at the corner? Ignatius. The hotdogs (and the molecules, etc.) were part of the cart that he labored to bring to the corner, and when the cart arrived, so did the hotdogs (and their molecular constituents[)].
Hal steps onto the court, serves, and so begins the tennis match. Very quickly, blood borne glucose is taken up through the cell membrane. Once inside, it is phosphorylated and bound into molecules of hexosediphosphate. This is not a case of simply being carried along for the ride. Hal’s muscle cells are, it is true, carried along when he swings his racket. But Hal’s tennis-playing also alters the behavior of innumerable biochemical pathways and cellular mechanisms that are involved in his tennis playing, both in the short-term and in the long-term. Why did Hal’s cells start using more glucose (i.e., binding glucose into molecules of hexosediphosphate)? Because Hal started to play tennis. Similar stories could be told about Hal’s respiratory mechanisms, visual system, and many others besides. Changing the behavior of the mechanism as a whole changed the activities of its components. It may be appropriate to say that the components are along for the ride, but if so, this is a different, more active, kind of ride than Ignatius’s hotdogs received. Hal’s glucoregulatory mechanisms are enlisted in the ride.