In this scholarly paper the author demonstrates how Freud's neo-Lamarckian statements were based on Darwin's own Lamarckian statements following the first edition of On the Origin of Species. Following his great discovery of natural selection Darwin was more and more compelled to acknowledge neo-Lamarckian mechanisms because his theory had posed serious problems and was being assailed by leading biologists and physicists of that period. It was only in the thirties, the last decade of Freud's life, that accumulated evidence from genetics and ecology strongly substantiated Darwin's thesis and ended the controversy.