In Popper Selections, A selection of Karl Popper’s writings, edited by David Miller, chapter 19 is titled “Natural Selection and Its Scientific Status.” In section II of this chapter Popper says that Darwin’s theory of natural selection is “difficult to test.” He talks about the tautological nature of the theory.
Then he says “I have changed my mind about the testability and the logical status of the theory of natural selection; and I am glad to have an opportunity to make a recantation.”
Later he says, “The theory of natural selection may be so formulated that it is far from tautological. In this case it is not only testable, but it turns out to be not strictly universally true.”
So what did Popper believe? Is natural selection scientific? Or is falsifiability stiil the only criterion for scientific validity?