Whales can weigh up to 300,000 pounds and live for 200 years or more. Nick Pyenson is the curator of fossil marine mammals at the Smithsonian Institution’s National Museum of Natural History in Washington. He joins us to talk about how whales evolved from land-roaming creatures – and about their prospects for survival in a warming world. His new book is called “Spying On Whales: The Past, Present, And Future of Earth’s Most Awesome Creatures” (Viking).