What are the motifs in The Beak of the Finch by Jonathan Weiner?

With any field of science, it is best to find the proof in nature rather than in a laboratory, but many people did not believe they could watch evolution any where but a laboratory with human intervention causing the changes. The thought was that humans could bring about changes in the laboratory that would be accelerated from those conditions in the wild. Although this does work, it does not prove anything would happen in the natural setting without the intervention of humans.