Smithsonian paleobiologist Nick Pyenson says about 40 to 50 million years ago whales had four legs and walked on land. Pyenson notes that the largest whales alive today are the biggest that have ever existed: “They are absolutely the largest vertebrate animals to have ever evolved in the history of life on Earth. No dinosaur was heavier.” He’ll explain how echolocation works, how they hold their breath for hours, and why we’re in the “golden age” of whale science. Pyenson’s new book is ‘Spying on Whales.’

Also, book critic Maureen Corrigan reviews ‘The Incendiaries: A Novel’ by R.O. Kwon.