Evolution and Testability
Creationists sometimes say that the theory of evolution is untestable and thus unscientific. This is a surprising claim, since creationists also say that the theory of evolution is incompatible with the second law of thermodynamics. If evolution were precluded by the second law, then evidence that confirms the second law would disconfirm the theory of evolution. If the theory of evolution can be disconfirmed, then it is testable. Creationists cannot have it both ways.
What is the source, then, of their claim that the theory of evolution is untestable? Let us ignore, for the sake of consistency, the creationist claim that the second law is incompatible with the theory of evolution and examine the grounds for the thesis that evolution is untestable. In the final analysis, I think the creationists' arguments fail miserably.
However, a caveat is necessary before we proceed. Creationists are mistaken in their presupposition that the theory of evolution must be classified as either a theory or a fact. One of the many problems with that presupposition results from the sloppy use of the indefinite article a in the phrase a fact. Such usage treats the theory of evolution as if it consisted of a single proposition whose evidential status is all-of-a-kind and which must be accepted or rejected as a whole. But if anything is evident, it is that the theory of evolution consists of many propositions whose evidential status is not all-of-a-kind. Proving the untestability of the theory of evolution, then, would consist of the piecemeal task of considering each separate proposition individually and demonstrating that each is untestable. Furthermore, since research is currently being done in evolutionary theory, not all of the propositions are in, making the task even more difficult. We need, therefore, to beware of hasty talk about the untestability of the whole theory.
Survival of the Fittest
But perhaps there is a proposition (or small set of propositions) that is so basic to evolutionary theory that showing its untestability would, like Descartes' evil genius, undermine the edifice upon which the theory is built, obviating the need for a "piecemeal" approach.
This, evidently, is the presupposition underlying the attack on natural selection. The argument occurs early in Henry Morris' book, Scientific Creationism: "A theory which incorporates everything really explains nothing! It is tautologous. Those who survive in the struggle for existence are the fittest because the fittest are the ones who survive" (p. 7). Stephen Jay Gould (1983) formulates the argument quite well before refuting it:
Natural selection is defined by Spencer's phrase 'survival of the fittest,' but what does this famous bit of jargon really mean? Who are the fittest? And how is 'fitness' defined? We often read that fitness involves no more than 'differential reproductive success'—the production of more surviving offspring than competing members of the population. Whoa! . . . This formulation defines fitness in terms of survival only. The crucial phrase of natural selection means no more than 'the survival of those who survive'—a vacuous tautology. [pp. 141-142]
Does this argument prove the untestability of the theory of evolution? A prerequisite for doing so is to show that the theory of evolution is built upon the edifice of natural selection in such a way that, without natural selection, the theory of evolution itself would collapse. That, however, is far from clear and certainly does not go without saying.
In response to creationist Duane Gish's assertion that the theory of evolution is a tautology without predictive value on the basis of the argument just cited, Gould writes: "Please note, however, that the false claim for tautology was advanced only against Darwin's mechanism of natural selection, not against the idea of evolution itself" (p. 140). In response to the claim that natural selection was quietly abandoned by even its most ardent supporters, Gould quips: "News to me, and I, although I wear the Darwinian label with some pride, am not among the most ardent supporters of natural selection" (p. 141). These remarks, if anything, suggest that the theory of evolution is independent of natural selection.
R. C. Lewontin (1981), another authority on the theory of evolution, inveighs against ". . . the growth of a vulgar Darwinism that sees direct adaptation in every feature of life. By making claims for natural selection that are as tortured as the absurd claims of the nineteenth century evolutionists who saw God's wisdom in everything, the vulgar adaptationists seriously weaken [the perception of] the power of evolutionary explanation." Now if only "vulgar" Darwinists make extravagant claims for natural selection, and thereby undermine the perception of the power of evolutionary explanation, then there are other mechanisms that explain evolutionary change, and the theory of evolution very well might be independent of natural selection.
Lewontin does mention other factors that play a role in evolutionary explanation:
The controversies about evolution lie in the realm of the relative importance of various forces in molding evolution. One such controversy concerns the relative importance of direct "adaptive" natural selection for characters, as opposed to other forces of evolution such as genetic drift, genetic linkage, pleiotrophy, allometry, and multiple adaptive peaks for particular events in evolution. [p. 559]
Two others might be mentioned: mutation and founder effect. Now if authorities cite many other factors involved in evolutionary change, debate the relative importance of natural selection, and suggest that the theory of evolution is independent of it, then creationists must first establish that the theory of evolution stands or falls with natural selection before their case can be made. But that issue is not even broached in their argument for evolution's circularity. Therefore, they have not proved the theory untestable.
A Criterion for "Fitness"
Nonetheless, they have made an important charge against natural selection itself: the charge of untestability. To answer this, it will be necessary to show that there is a criterion other than survival for something being the "fittest" or better adapted. Is there an independent criterion?
Gould tells us that there is. He says that the survival and spread of certain traits in individuals throughout populations is a result of the fitness (adaptability) of those traits, not a definition of fitness (p. 143). Certain traits are superior or better adapted before they survive and spread. I quote Gould:
Now, the key point: certain morphological, physiological, and behavioral traits should be superior a priori as designs for living in new environments. These traits confer fitness by an engineer's criterion of good design, not by the empirical fact of their survival and spread. [p. 143]
A trait is better adapted, then, if it meets an engineer's criterion of good design. Although the word design may prompt some to think of a popular argument for God's existence, the criterion Gould invokes is naturalistic. It is a matter of comparing an engineer's design of something with what one finds in nature. The better adapted or "fitter" organisms are those which would meet an engineer's criterion for good design if an engineer were to apply one. If one then predicts that organisms which meet an engineer's criterion would be those that survive and, in the long run, spread their traits throughout populations, then such a prediction in terms of natural selection is testable.
The criterion Gould cites is general and designed to cover all cases. But it is not clear how this criterion plays a role in evolutionary explanation. Let us turn, then, to a specific example in order to clarify the testable and contingent character of possible explanations in terms of natural selection.
The example I shall cite is one that the creationists deny is an instance of evolution "in the true sense." An evolutionary process is a change in gene frequency that, in the long run, results in the appearance of a new species. The example I shall cite is not one in which a new species appeared. Those changes take so long that it is impossible for an individual to point to one having occurred in his or her personal experience. But the creationists' denial that it is an instance of evolution "in the true sense" is irrelevant here, for the issue has to do with the testability of explanations in terms of natural selection. And the example I shall cite is undoubtedly an instance of natural selection.
My example is a standard one about the peppered moths in England. Before 1845, every observed moth of this kind was gray (at least every recorded observation). In 1845, however, a single black moth of that biological type was observed and recorded in Manchester, an industrialized area. Presumably, there were more black moths. Now the gray color of most of the moths was better adapted to their environment, since the moths tended to stay on trees that were covered with gray lichens. Thus, the gray color constituted a good camouflage against their predators (primarily birds). On the other hand, the darker moths were less well camouflaged and even tended to stand out against the background of the trees on which they lived. They were therefore less well adapted. Now, since the darker moths were easier for the birds to see, they would, as a group, more likely be eaten before they matured and reproduced. Since physical characteristics are inherited, it could, at this point, be predicted that, if the environment remained the same in the relevant respects, the black moths would constitute a smaller percentage of the population, whereas the gray ones would comprise a larger one. If you were to design a moth for living in such an environment, you would give it good camouflage against its predators. The gray moths in that environment meet the engineer's criterion of good design.
But the environment did not remain the same. Industrialization in England blackened the trees, making the gray moths more easily visible to their predators, whereas the black ones had thus become less easily visible. It could then be predicted that the percentage of black moths would increase, whereas the gray ones would decrease (Northington and Goodin, 1984). In this new environment, the dark moths meet the engineer's criterion of good design.
Now it is a logically contingent fact that the better camouflaged moths survive and, in the long run, spread their better-adapted characteristic throughout the population. I would not place my bet on the survival and spread (or even stability) of the black moths when the trees are gray, nor on the gray ones when the trees are black. However, it is not true by definition that the better-adapted (in this instance, better camouflaged) individuals will survive and spread. Their greater adaptation relative to environmental conditions is identifiable independently of and prior to their survival, as shown by the predictions those identifications license. If those predictions were disconfirmed by subsequent observations, that would be evidence against natural selection as an explanation of the evolutionary change. The possibility of such disconfirming evidence constitutes testability.
This example is not atypical. Basically, it is a matter of being able to identify those characteristics that, in a given environment, would be more likely to produce survival and spread. But survival, once again, is not a definition of adaptability but a probable result of it. Creationists have not, therefore, proven the untestability of explanations in terms of natural selection, much less the untestability of the theory of evolution.
One harmless concession should be made. Gould does note that some of the literature in evolutionary theory does involve the use of a circular criterion of fitness or adaptability (p. 143). Gould, and I think rightly, attributes this to an unwillingness among some scientists to "explore seriously the logical structure of arguments" (p. 141). Some scientists need, in short, to be more philosophical. But this does not mean that the theory of evolution or Darwin's formulation is untestable, since good explanations and predictions in terms of natural selection can be specified in a noncircular way, and frequently are.
Ehrlich and Birch
The argument I have refuted is not, however, the only argument for the untestability of the theory of evolution in Scientific Creationism. Consider this argument from page nine:
It is clear that neither evolution nor creation is, in the proper sense, either a scientific theory or a scientific hypothesis. Though people might speak of the "theory of evolution" or of the "theory of creation," such terminology is imprecise. This is because neither can be tested. A valid scientific hypothesis must be capable of being formulated experimentally, such that the experimental results either confirm or reject its validity.
As noted in the statement by Ehrlich and Birch cited previously, however, there is no conceivable way to do this.
The claim that the theory of evolution is untestable is based upon the assertion that evolution is not a valid scientific hypothesis that is capable of being formulated experimentally, such that the experimental results either confirm or reject its validity. Ehrlich and Birch's authority is cited as grounds for asserting this.
If one reads only the creationists' quotation from Ehrlich and Birch's article, one would think that Ehrlich and Birch believe that the theory of evolution as a whole is untestable. That impression, however, would be far from the truth, since the creationists have, by quoting Ehrlich and Birch out of context, distorted their views. This is the quotation in Scientific Creationism:
Our theory of evolution has become . . . one which cannot be refuted by any possible observations. It is thus "outside of empirical science," but not necessarily false. No one can think of ways in which to test it. . . . (Evolutionary ideas) have become part of an evolutionary dogma accepted by most of us as part of our training. [pp. 6-7]
The creationists did not cite the very next sentence: "The cure seems to us not to be a discarding of the modern synthesis of evolutionary theory, but more skepticism about many of its tenets" (Ehrlich and Birch, p. 352). If Ehrlich and Birch think that the theory of evolution as a whole is untestable, why do they say, in the very next sentence, that evolutionary theory should not be scrapped? The answer is that they do not regard the theory of evolution as a whole to be untestable, as even a cursory reading of the article shows. At the beginning of Ehrlich and Birch's article, offset and in boldface, is a good precis:
While accepting evolutionary theory, should ecologists be more skeptical about hypotheses derived solely from untestable assumptions about the past? The authors put forward the view that many ecologists underestimate the efficacy of natural selection and fail to distinguish between phylogenetic and ecological questions. [p. 349]
These two biologists are not at all dissatisfied with the theory of evolution as such.
They are dissatisfied, however, with how some scientists make use of some hypotheses about the evolutionary past. The article is about how some ecologists investigate matters poorly by turning too readily to untestable assumptions about the past to answer their questions rather than first turning to explanations that are falsifiable. Ehrlich and Birch write, for example:
It is clear that considerably more thorough investigations of the present day population biology of these birds, with the emphasis on the genetics of clutch size, magnitude of selection pressure on clutch size, and rates of gene flow, will be necessary before we fall back on an untestable historical hypothesis. [p. 350]
In brief, those ecologists who investigate poorly have used untestable historical hypotheses to circumvent the need for more empirical investigation, which is objectionable. [This is not to imply that historical hypotheses are automatically untestable; see the next article, page nine.]
Ehrlich and Birch also say that the tendency of some ecologists to turn too quickly to untestable historical hypotheses has been accompanied by a failure to address logically prior questions and confusions about what constitutes a proper scientific explanation (pp. 350-351).
What are these untestable historical hypotheses? They are very specific assertions about specific animals in specific locations. One example is about the ancestral habitat of the British great tit, Parus major. Another is about competition in the past between two species of birds on the Canary Islands, Fringella coelebs and Fringella coerulea (p. 350). The point is that these hypotheses are about specific details of evolutionary history. These hypotheses are quite peripheral. They are not fundamental propositions in the theory of evolution. They are not even relatively important to the theory as a whole but represent only some sloppy work on the part of some ecologists. The untestability of these speculations about very specific details, therefore, does not imply that fundamental or relatively important propositions of evolutionary theory are untestable. In fact, such propositions as "More complex lifeforms have developed out of simpler ones" and "Dinosaurs existed and became extinct long before modern humans came into existence" are testable. The evidence could disconfirm them, but it simply does not. No doubt Ehrlich and Birch recognize this, which is why they recommend that evolutionary theory be retained.
Furthermore, Ehrlich and Birch not only favor retaining evolutionary theory but also criticize their colleagues for failing to appreciate "the efficacy of natural selection." As I pointed out earlier, creationists believe that explanations in terms of natural selection are untestable. To say the least, it is not in their best interest to cite as authoritative such strong advocates of the explanatory power of natural selection.
We have examined two arguments in Scientific Creationism for the untestability of evolutionary theory. The first, concerning the alleged circularity of natural selection, rested upon an unproven presupposition and included the false premise that survival is the test of adaptability. The second involved an appeal to the authority of Ehrlich and Birch. Examining what they had to say, however, showed that their article did not advance the creationist's case. If the creationists believe that the theory of evolution stands of falls with a peripheral hypothesis about the great British tit, they must be guilty of a confusion to which I alluded at the beginning of this article—that of thinking of evolutionary theory as a single proposition whose evidential status is all-of-a-kind.
Furthermore, the evidence could have corroborated (but does not) the hypothesis that all lifeforms appeared at virtually the same time. As a result, it is not only true that creationists have failed to prove the untestability of the fundamental tenet of evolutionary theory, it is also true that the fundamental tenet is testable.
The same cannot be said of the fundamental axiom of creationism, that God wrote Genesis.
According to the Biblical record, God Himself wrote with His own hand these words: "For in six days the Lord made heaven and earth, the sea, and all that in them is. . . ." That being true, it follows that real understanding of man and his world can only be acquired in a thorough-going creationist frame of reference. [Morris, p. iii]
I should like to show the untestability of that creationist axiom and others. That, however, is a different topic.
Ehrlich, P. R., and Birch, L. C. April 22, 1967. "Evolutionary History and Population Biology." Nature, volume 214.
Gould, S. J. 1983. "Darwin's Untimely Burial—Again!" in L. R. Godfrey (editor), Scientists Confront Creationism. New York: W. W. Norton and Co.
Lewontin, R. C. September 1981. "Evolution/Creation Debate: A Time for Truth." Bioscience, 31:8.
Morris, H. M. (editor). 1974. Scientific Creationism (general edition). San Diego: Creation-Life Publishers.
Northington, D. K., and Goodin, J. R. 1984. The Botanical World. St. Louis: Times Mirror/Mosby; pp. 408-409.