'99 Seminar, Philosophy of Biology
Popper on Darwinism
(From his "Autobiography" in The Philosophy of Karl Popper, part I, Open Court, 1974)
"I have come to the conclusion that Darwinism is not a testable scientific theory, but a metaphysical research programme---a possible framework for testable scientific theories. "(134)
Popper reformulates Darwinism as follows:
(1) The great variety of the forms of life on earth originate from very few forms, perhaps even from a single organism: there is an evolutionary tree, an evolutionary history.
(2) There is an evolutionary theory which explains this. It consists in teh main of the following hypotheses.
(a) Heredity: the offspring reproduce the parent organisms fairly faithfully.
(b) Variation: there are (perhaps among others) "small" variations. The most important of these are the "accidental" and hereditary mutations.
(c) Natural selection: there are various mechanisms by which not only the variations but the whole hereditary material is controlled by elimination. Among them are mechanisms which allow only "small" mutations to spread; "big" mutations ("hopeful monsters") are as a rule eliminated.
(d) Variability: although variations in some sense---the presence of different competitors---are for obvious reasons prior to selection, it may well be the case that variability---the scope of variation---is controlled by natural selection; for example, with respect to the frequency as well as the size of vatiations. (135-6)
Then he continues:
It is metaphysical because it is not testable. . . . For assume that we find life on Mars consisting of exactly three species of bacteria with a genetic outfit similar to that of terrestrial species. Is Darwinism refuted? By no means. We shall say that these three species were the only forms among the many mutants which were sufficiently well adjusted to survive. And we shall say the same if there is only one species (or none). Thus Darwinism does not really predict the evolution of variety. It therefore cannot really explain it. At best, it can predict the evolution of variety under "favorable conditions". But it is hardly possible to describe in general terms what favorable conditions are---except that, in their presence, a variety of forms will emerge. (136)
Take "adaptation". At first sight natural selection appears to explain it, and in a way it does, but it is hardly a scientific way. To say that a species now living is adapted to its environment is, in fact, almost tautological. Indeed we use the terms "adaptation" and "selection" in such a way that we can say that, if the species were not adapted, it would have been eliminated by natural selection. Similarly, if a species has been eliminated it must have been ill adapted to the conditions. Adaptation or fitness is defined by modern evolutionists as survival value, and can be measured by actual success in survival: there is hardly any possibility of testing a theory as feeble as this. (137)
However, these criticisms do not mean that Popper considers Darwinism as of little value. He tries to exploit an analogy between Darwinism and his own falsificationism, and he proposes a sort of evolutionary epistemology with respect to the development of scientific knowledge.
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January 28, 1999. (c) Soshichi Uchii
suchii@bun.kyoto-u.ac.jp
