First, for those who do not know of Sir Karl Popper, we should state that his philosophical views carry considerable weight in scientific circles. He has described how science should work and how its hypotheses should be tested. In this sense, he has defined what is scientific and what isn't.
Now, back to the Medawar Lecture, as recounted by M. Perutz. Popper declared his detestation of determinism in all its guises. "Popper disputes the existence of historical laws and holds that our future is in our own hands." Zeroing in on evolution, Popper accepts Darwinism in the sense that "organisms better adapted than others are more likely to leave offspring." He then splits Darwinism into passive and active forms. His passive variety of evolution is that which is currently in vogue -- the deterministic view that random mutation combined with natural selection invariably leads to higher forms of life. But, as already stated, Popper hates determinism and believes that deterministic mechanisms are noncreative. They lead only to deadends. Instead, he prefers "active" Darwinism in which the "idiocyncracies of the individual have a greater influence on evolution than natural selection" and that "the only creative activity in evolution is the activity of the organism."
There you have it! Whose side is Popper on? Does it really matter?
(Perutz, Max; "A New View of Darwinism," New Scientist, p. 36, October 2, 1986.)
Comment. It is unclear how the acts of individuals can modify organisms. Sounds like Lamarckism.