What is the theme in God Emperor of Dune by Frank Herbert?

Survival of the fittest is a major theme. God Emperor of Dune is about the institution of the "Golden Path," Leto II's radical program for ensuring the survival of the human race. This is signaled by the first action scene, in which rebels race through the Forbidden Forest, pursued by D-wolves, and only the athletic Siona survives. Notably, she carries a sealed packet they have stolen from the fortress, which they hope will reveal where Leto hides his hoard of melange-spice, but also she is an Atreides, the product of selective breeding over millennia.