David Callahan, founder and editor of the website Inside Philanthropy, and co-founder of Demos, investigates how a new generation of billionaire philanthropists rallying behind causes like the environment and education are influencing government policy. Writer and director James Gray discusses his new film, “The Lost City of Z.” The film tells the true story of an early 20th-century British explorer named Percy Fawcett, whose search for an ancient lost city in the Amazon consumed him. Actors Harvey Fierstein, Gabriel Ebert and Christopher Sears discuss “Gently Down the Stream." Fierstein stars as Beau, an expat living in London, who meets a young lawyer named Rufus at the dawn of online dating. Alvin and Lawrence Ubell, our Gurus of How-To, return just in time for spring to answer our listener questions about home repairs and projects.