Throughout Prodigal Summer, characters debate whether humans have the right to control the natural world, or whether people instead have a responsibility to maintain the intrinsic balance of nature. For Garnett Walker and Nannie Rawley, the debate becomes a matter of religion, as well; for other characters, these questions influence relationships and their overall outlook on life.

Garnett and Nannie play out their disagreements most explicitly, through a series of letters that begin as an argument about Nannie’s dislike for herbicides and her insistence on saving living creatures and evolve into greater questions of philosophy. Garnett’s initial letter insists that according to the Biblical story of Genesis, men are the “keepers and guardians of the earth” and have the right to use God’s other creations “for our own purposes,” even if doing so causes some species “to go extinct after a while” (186-87). In her response, Nannie also refers to Genesis, but claims that Garnett has misunderstood the Biblical passage. She argues that if “God gave us” all the wonders of the natural world, then even the smallest of these wonders—the “weeds and pond algae”—are sacred (217).

Garnett and Nannie’s exchange evolves from letters into spoken arguments, pitting Nannie’s faith in evolution against Garnett’s Creationism.