In recent years, psychologists, economists and neuroscientists have shed light on these questions. Their ideas have attracted popular interest, but haven’t changed the way most conservation organizations work. Only a tiny percentage of the money...

The locals said it could not be done. It was 1999, and the hardheaded ecologist J. Michael Fay was determined to tromp across 2,000 miles of the Congo Basin. In a northeastern patch, he ran into a swampy tangle so thick that he struggled to advance...