Weiner opens with an anecdote of Peter and Rosemary Grant at work in 1991, on the island of Daphne Major in the Galápagos archipelago. They catch a finch that has long eluded them, measure its dimensions, and band its leg. The scene depicts the pair as passionate and adventurous experts on the birds. Weiner invokes religion to describe their devotion to their work, which they have been doing for nearly two decades: “like sentries […] like shepherds, or like Bible scholars” (3). On Daphne, the Grants continue the work of Charles Darwin, the founder of evolutionary theory, in the place where he discovered the finches a century earlier.

In his 1859 work On the Origin of Species by Means of Natural Selection, Darwin outlined a groundbreaking theory of continuous change in living organisms, in which “natural selection is daily and hourly scrutinizing, throughout the world, the slightest variations; rejecting those that are bad, preserving and adding up all that are good […]” (6). He compiled compelling suggestive evidence that evolution happens, but he never documented the process in action, thus leaving his theory vulnerable to refutation and intense debate.