Excursus: Defining Downward Causation

There has been a developing literature on downward or top-down causation over the past 40 years. Philosophical theologian Austin Farrer was clearly groping for such a concept in his 1957 Gifford Lectures. Seeking a way to argue that higher-level patterns of action . . . may do some real work and thus not be reducible to the mass effect of lower-level constituents, he says that "in cellular organization the molecular constituents are caught up and as it were bewitched by larger patters of action, and cells in their turn by the animal body" [10]. Farrer's metaphor of higher-level organizations bewitching the lower-level constituents is the sort of talk that deepens the mystery rather than clarifies it.

Psychologist Roger Sperry sometimes speaks of the properties of the higher-level entity or system overpowering the causal forces of the component entities [11]. However, elsewhere Sperry refers to Donald Campbell's account of downward causation. Here there is no talk of bewitching or overpowering lower-level causal processes, but instead a thoroughly non- mysterious account of a larger system of causal factors having a selective effect on lower-level entities and their causal effects. Campbell's example is the role of natural selection in producing the efficient jaw structures of worker termites and ants.

Consider the anatomy of the jaws of a worker termite or ant. The hinge surfaces and the muscle attachments agree with Archimedes' laws of levers, that is, with macromechanics. They are optimally designed to apply maximum force at a useful distance from the hinge. . . . This is a kind of conformity to physics, but a different kind than is involved in the molecular, atomic, strong and weak coupling processes underlying the formation of the particular proteins of the muscle and shell of which the system is constructed. The laws of levers are one part of the complex selective system operating at the level of whole organisms. Selection at that level has optimised viability, and has thus optimised the form of parts of organisms, for the worker termite and ant and for their solitary ancestors. We need the laws of levers, and organism-level selection . . . to explain the particular distribution of proteins found in the jaw and hence the DNA templates guiding their production [12].

Downward causation, then, is a matter of the laws of the higher-level selective system determining in part the distribution of lower-level events and substances. "Description of an intermediate-level phenomenon," he says, "is not completed by describing its possibility and implementation in lower-level terms. Its presence, prevalence or distribution (all needed for a complete explanation of biological phenomena) will often require reference to laws at a higher level of organisation as well" [13].

Campbell uses the term "downward causation" reluctantly. If it is causation, he says, "it is the back-handed variety of natural selection and cybernetics, causation by a selective system which edits the products of direct physical causation" [14]. We can represent the bottom-up aspect of the causation as in Figure 3:

Figure 3 
(click to enlarge).

That is, the information encoded in the DNA contributes to the production of certain proteins upon which the structure of the termite jaw supervenes. This is micro-physical or bottom-up causation.

However, to represent the top-down aspect of causation, we need a more complex diagram, as in Figure 4, representing feedback from the environment, E. Here the dashed lines represent the top-down aspects, solid lines represent bottom-up causation.

Figure 4 
(click to enlarge).

The most helpful recent account of top-down causation is Robert Van Gulick's [15]. Van Gulick makes his points about top-down causation in the context of an argument for the nonreducibility of higher-level sciences. The reductionist, he says, will claim that the causal roles associated with special-science classifications are entirely derivative from the causal roles of the underlying physical constituents of the objects or events picked out by the special sciences. Van Gulick replies that although the events and objects picked out by the special sciences are composites of physical constituents, the causal powers of such an object are not determined solely by the physical properties of its constituents and the laws of physics, but also by the organization of those constituents within the composite. And it is just such patterns of organization that are picked out by the predicates of the special sciences. Another way to make the same point is to say that physical outcomes are determined by the laws of physics together with initial and boundary conditions. Thus, Van Gulick concludes, "we can say that the causal powers of a composite object or event are determined in part by its higher-order (special science) properties and not solely by the physical properties of its constituents and the laws of physics" (p. 251). The patterns of boundary conditions picked out by the special sciences have downward causal efficacy in that they can affect which causal powers of their constituents are activated or likely to be activated.

A given physical constituent may have many causal powers, but only some subsets of them will be active in a given situation. The larger context (i.e. the pattern) of which it is a part may affect which of its causal powers get activated. . . . Thus the whole is not any simple function of its parts, since the whole at least partially determines what contributions are made by its parts. (p. 251)

Here we see a generalization of Campbell's insight that downward causation is not overpowering but selective activation of lower-level causal processes.

Footnotes for Downward Causation

[10] Austin Farrer, The Freedom of the Will, the Gifford Lectures, 1957 (New York: Charles Scribner's Sons, 1958), 57.

[11] Roger W. Sperry, Science and Moral Priority: Merging Mind, Brain, and Human Values (New York: Columbia University Press, 1983), 117.

[12] Donald T. Campbell, "'Downward Causation' in Hierarchically Organised Biological Systems," in F.J. Ayala and T. Dobzhansky, eds., Studies in the Philosophy of Biology: Reduction and Related Problems (Berkeley and Los Angeles: University of California Press, 1974), 179-186; 181.

[13] Ibid., 180.

[14] Ibid., 180-81.

[15] Robert Van Gulick, "Who's in Charge Here? And Who's Doing All the Work?" in Heil and Mele, eds., Mental Causation, 233-256.