SAPOLSKY: I just started a biography of Peter Kropotkin by George Woodcock and Ivan Avakumovi?. Kropotkin was a Russian prince who renounced his title, became an anarchist and wrote a textbook of evolutionary behavior about 80 years ahead of everyone else. I also just started this big and depressing dual biography of Hitler and Stalin by this British historian, Laurence Rees. I’m trying to figure out who’s more of a monster, Stalin or Lenin. I leapt into that after finishing his cheery book “The Holocaust: A New History.” He talked to survivors and perpetrators of the horrible atrocities committed during...