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What Did Karl Popper Really Say About Evolution?
In a 1981 article in Science Digest, Duane Gish, the master debater among creationists, said:
The most direct rebuttal one can give to these charges is that Gish and other creationists really don't believe them! The underlying point of the above quotation is that evolution is unscientific because it is not falsifiable (testable), yet creationists are always producing arguments and "evidences" that they say refute evolution. Gish does it in the article quoted above. In spite of that obvious contradiction, the argument impresses laypeople and legislators. But it completely distorts what Popper calls the logic of scientific discovery.
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So what does Popper really say about evolution?
Furthermore, in his book, Objective Knowledge, where he uses the Darwinian paradigm as a basis for his own theory of knowledge, Popper not only discusses Darwinism at length as a scientific explanation but offers as an additional component a scientific hypothesis of his own—genetic dualism—which is intended to strengthen the orthodox neo-Darwinian framework (Popper, 1972, p. 242 ff). Popper's genetic dualism is similar to the ideas of Wilson and Stebbins (Stebbins, 1977, p. 125) and Mayr (1963, p. 604 ff.; 1970, p. 363 ff.) concerning the role of behavior in evolution.
But he did make one mistake—for which we should forgive him; some well-known biologists (who should know better) have made the same mistake. Popper takes "survival of the fittest" as the definition of natural selection (Popper, 1972, p. 241). This catchy phrase was an invention of Herbert Spencer, which Darwin, in a rare example of bad judgment, interpolated into later editions of On the Origin of Species: "This preservation of favorable individual differences and variations and the destruction of those which are injurious I have called Natural Selection or the Survival of the Fittest" (p. 64). Clearly it is an alternate name (and not a very apt one) for the process in question but not a definition.
The argument regarding "survival of the fittest" is that the only way one can usually tell who the fittest are is to see who survives. But then survival of the fittest becomes "almost a tautology" and hence untestable (Popper, 1972, p. 69; 1963a, p. 964).
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It is clear that here Darwinism means natural selection, not evolution. Popper states this explicitly earlier in the same work:
There are two points to be made here:
First, natural selection being untestable is not the same as evolution being untestable. Evolution, to the creationist, is any hypothesis about origins. Astrophysical theories about stellar evolution or the "Big Bang" cosmology or scientific geology or, for that matter, many facets of biological evolution are not based upon Darwinian natural selection.
Second, Popper later admitted that he was wrong!
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Thus the creationists were never correct in stating that Popper believed that evolution was not falsifiable (and hence not scientific), nor are they now correct in citing him as an authority for the claim that natural selection is tautological and not falsifiable!
Some might challenge my point that Popper never doubted the testability of evolution by citing the following:
But in an earlier work, he explicitly identified these "vapors" as "the Great Systems of Evolutionist philosophy, produced by Bergson, Whitehead, Smuts and others" (Popper, 1957, p. 106). He was not speaking, then, of the scientific theory of evolution but of various metaphysical theories. He made a clear distinction between the two.
And his current support for the Darwinian idea of natural selection is expressed in equally plain language.
As for the notion of design as a useful hypothesis:
There are scientists who are unfamiliar with or misinterpret Popper. For example, Colin Patterson holds that, if we accept Popper's distinction between science and nonscience, evolution is not science because it deals with unique historical events. Popper, however, doesn't agree with this.
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In an earlier work, Popper discussed the historical sciences in which the scientific method of theoretical sciences is used:
What Popper calls the historical sciences do not make predictions about long past unique events (postdictions), which obviously would not be testable. (Several recent authors—including Stephen Jay Gould in Discover, July 1982—make this mistake.) These sciences make hypotheses involving past events which must predict (that is, have logical consequences) for the present state of the system in question. Here the testing procedure takes for granted the general laws and theories and is testing the specific conditions (or initial conditions, as Popper usually calls them) that held for the system.
A scientist, on the basis of much comparative anatomy and physiology, might hypothesize that, in the distant past, mammals evolved from reptiles. This would have testable consequences for the present state of the system (earth's surface with the geological strata in it and the animal and plant species living on it) in the form of reptile-mammal transition fossils that should exist, in addition to other necessary features of the DNA, developmental systems, and so forth, of the present-day reptiles and mammals.
What about repeatability? It is the observations that must be repeatable, if only to establish their validity independently of any one person's authority. This does not mean that the hypothetical mechanism or the phenomenon concerned must be repeatable or reproducible. In the experimental laboratory where the phenomena being studied are short-lived and transient, it is usually necessary to reproduce them in order to repeat the observations. But scientists must wait for the recurrence of natural phenomena—such as eclipses, earthquakes, seasonally recurring biological phenomena, and so forth. Yet, if a phenomenon is a stable, more or less permanent long-term condition, observations may be repeated anytime. A geologist may return to a geological formation to repeat or make new observations, or an anatomist or paleontologist may reexamine a museum specimen, either corroborating or refuting someone else's previous observations. Clearly, then, a hypothesis postulating a unique past event is scientific—as long as it has observable consequences for the present that can be repeatedly verified by any observer.
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Thus we may conclude (as Popper did) that evolutionary theories or historical hypotheses about origins are no different than other scientific theories as far as their logical features are concerned and are just as falsifiable as hypotheses in the form of general laws and theories.
Asimov, I., and Gish, D. T. October 1981. "The Genesis War: A Debate." Science Digest, p. 82.
Darwin, C. (n.d.) On the Origin of Species and the Descent of Man. New York: Modern Library.
Halstead, B. 1980. "Popper: Good Philosophy, Bad Science?" New Scientist, 87: 215-217.
Mayr, E. 1970. Population, Species, and
Evolution. Cambridge, MA: The Belknap Press.
Popper, K. R. 1981. Letter.
New Scientist, 87:611.
Stebbins, G. L. 1977. Processes of Organic Evolution, third edition. Englewood Cliffs, NJ: Prentice-Hall.
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