From Introduction:

DARWIN'S WORLD is a role-playing game set in the wild inhospitable world of mankind's ruin, decades after a series of devastating wars that brought the human race to the brink of extinction. In a world where radiation altered the very course of nature, mankind ceased to exist in its current form. Mutations and genetic variations are the edge separating a species from life and death.
In DARWIN'S WORLD, only the fit shall survive!