What are the motifs in The Metaphysical Club: A Story of Ideas in America by Louis Menand?

Evolution is a recurring idea in the book. Theories of evolution began before Darwin, but Darwin put the ideas out to the public. He was not truly an evolutionist, but he did believe in the natural selection. Nature decided what was best for each species and mutated the species to have what was needed. He used his finding of flora and finches to come up with this theory.