"Theory" in the abstract, and in the concrete

However, no one disputes that natural selection is a principle that must operate, and must have operated, in populations of living organisms.

To move beyond a purely semantic dispute, one must distinguish two senses of the word "theory". A theory in the concrete, which one may call "theory_C", makes some claim about the world as it is. A theory in the abstract, theory_A, makes no claim about the world as it is, but only as it might be (i.e., if certain conditions obtains). When one refers to "population-genetics theory" or "selection theory" or to "X theory", this is usually a reference to theory_A, a body of inter-related statements that are assumed to be logically consistent. One doesn't usually use the words "true" and "false" to refer to theory_A. A piece of theory_A is "true" if it is logically consistent, regardless of what the world is like; a theory_A is "false" only if it incorporates some mathematical or logical error. When we refer to a "theoretician", we are usually referring to someone who explores and develops theory_A, rather than someone who evaluates hypotheses using experiment and observation.

By contrast, when we hear references to "the theory of X" or "Bob's theory of the universe" or the "the X-istic theory", this is usually theory_C, a set of interconnected statements that purport to explain something, to describe how the world works. In English, the presence of the definite article "the" signals the concreteness of theory_C. The distinction between theory_C and "hypothesis" is an issue upon which no two scientists will agree. In my opinion, theories_C represent a subset of hypotheses. Usage clearly favors theory_C for "big" or comprehensive hypotheses (ones that connect many observations and principles), or for hypotheses that have some history of support. The truth value of a theory_C (unlike that of a theory_A) is evaluated by experiment and observation.

Sometimes one hears the claim that, in science, "theory" refers to hypotheses that have been repeatedly confirmed and that are widely accepted by the scientific community, but (not to put too fine a point on it) this is a ridiculous position. One only hears of this interpretation of "theory" in discussions of evolution, because it arises from the ulterior motive of a definition of "theory" to defend Darwinism as a "theory". In general, this dubious and transparent attempt to associate "theory" with Truth ignores the well established double duty of "theory" for both abstract and concrete senses, as well as the subtle and often imperceptible difference in usage between "theory" (theory_C) and "hypothesis" (the latter of which doesn't work well in arguments with creationists, who have their own ulterior motives for interpreting "hypothesis" as "guess").

Now, to return to "Darwinism" and "neo-Darwinism". Darwinism, as theory_C, is dead, because Darwin's theory of variation is at odds with real-world genetics. We need a different theory_C that incorporates Darwin's abstract (theory_A) principle of natural selection. What about neo-Darwinism? As theory_C, neo-Darwinism must make certain claims that apply to the world (i.e., they are not merely theory_A statements of principles), and that do not simply repeat well known observations. We cannot simply say "selection occurs, selection must occur", and call this theory_C, because it is not. One must make significant and non-obvious claims about the world.

One way of viewing this criterion of making significant non-obvious claims is that the theory_C must make some claim of "explanatory sufficiency", that is, it must propose that the assumptions and the logical structure of the theory provide a sufficient basis to account for some set of phenomena that may be observed in the real world.

Although most contemporary biologists are hesitant to make any such claims from evolutionary theory (a sad state of affairs!), other contemporary biologists are not, and past generations were not shy at all. A statement quoted in the next section provides a clear example of connecting the abstract parts of a theory with a concrete claim of explanatory sufficiency (Stebbins, 1966):

mutations are rarely if ever the direct source of variation upon which evolutionary change is based. Instead, they replenish the supply of variability in the gene pool which is constantly being reduced by selective elimination of unfavorable variants. Because in any one generation the amount of variation contributed to a population by mutation is tiny compared to that brought about by recombination of pre-existing genetic differences, even a doubling or trebling of the mutation rate will have very little effect upon the amount of genetic variability available to the action of natural selection. Consequently, we should not expect to find any relationship between rate of mutation and rate of evolution. There is no evidence that such a relationship exists.