Reports of the National Center for Science Education

Popper and Evolution

Popper and Evolution
Reviewed by
Stephen G. Brush

In connection with the discussion of Karl Popper's philosophy of science (Reports 13(1) and 13(3)), it should be recalled that this philosophy played a small but significant role in the creation-evolution controversy in the early 1980s, and it is still used by anti-evolutionists a decade later.

Popper asserted that making testable (and thus potentially falsifiable) predictions of previously unobserved phenomena was a necessary condition for a theory to be called "scientific." This was known as the "falsifiability" criterion. Popper himself concluded that Darwinian evolutionary theory failed to satisfy that criterion so it was not a scientific theory but only a metaphysical research programme--a way of explaining what had already happened, not a theory that can predict what will happen in the future.

There is an obvious flaw in the criterion, at least in the extreme version originally proposed by Popper: it excludes not just evolutionary biology but also historical geology and much of astronomy, even though these are recognized sciences. A more subtle objection is that even in testing theories that obviously are scientific, such as Einstein's general theory of relativity, scientists do not give any more weight to previously unknown phenomena (such as the bending of light by the Sun) than to deductions of known phenomena (such as the advance of the perihelion of Mercury).

Popper reversed himself in 1978 and asserted that Darwinian theory is scientific. But the damage had been done; creationists used Popper's original statement to argue that evolution is not a science and hence does not deserve precedence over creationism in the classroom. For example, in 1982 a proposed "equal-time" law in Maryland argued that "evolution-science like creation-science cannot be ... logically falsified."

In a society where the word "science" implies reliable knowledge and the authority that goes with such knowledge, lots of people (especially including creationists) want to grab that label, and many of us feel a strong need for an objective test or formula to distinguish between science and nonscience. Popper's falsification criterion once seemed to be the answer, but it was too simplistic. I don't think there is a single test that can capture the multidimensional nature of real science. At the same time we can insist on several factors that should be involved in judging theories: internal coherence, compatibility with other accepted theories, agreement with empirical evidence, etc. A careful reading of Popper's works shows that he advocated such a multifactor approach when he wasn't discussing the falsifiability criterion which made him famous. (References for the statements mentioned here can be found in my article in Science, 1 December 1989.)

Ed.: C/E Issue VI, 1981, quotes Popper's "reversal" directly in "Misquoted Scientists Speak Out," by J. Cole.

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