Natural selection has been described as an environment selectively screening for those who will have progeny. Where humans are concerned, though, this is an extremely limiting viewpoint. Reproduction by sex tends toward experiment and innovation. It raises many questions, including the ancient one about whether environment is a selective agent after the variation occurs, or whether environment plays a pre-selective role in determining the variations which it screens. Dune did not realty answer those questions: it merely raised new questions which Leto and the Sisterhood may attempt to answer over the next five hundred generations.
Attributed to: Harq al-Ada
From Chapter 44 of Children of Dune by Herbert, Frank