 Popper later changed his view, concluding that the theory of natural selection is falsifiable and that Darwin's own example of the peacock's tail had disproved one extreme variation of it, that "all" evolution is driven by natural selection.Although in 1978 Popper wrote that his earlier objection had been specifically to the theory of natural selection, in lectures and articles from 1949 to 1974 he had stated that "Darwinism" or "Darwin's theory of evolution" was a "metaphysical research programme" because it was not falsifiable.In fact he continued to express dissatisfaction with contemporary statements of the theory of evolution which focused on population genetics, the study of the relative frequencies of alleles (different forms of the same gene).