NEW ORLEANS—People walking around the Sheraton Hotel here are talking about population as if it were the most natural conversation in the world. The topic interests me, so I join in. As it happens, I’ve written a book on it, just published by...

NEW ORLEANS—People walking around the Sheraton Hotel here are talking about population as if it were the most natural conversation in the world. The topic interests me, so I join in. As it happens, I’ve written a book on it, just published by...