Silk—prized for its lightness, luminosity, and beauty—is also one of the strongest biological materials ever known. More than a century ago, it was used to make the first bulletproof vest, and yet science has barely even begun to tap its potential. As the technologies it has inspired—from sutures to pharmaceuticals, replacement body parts to holograms—continue to be developed in laboratories around the world, they are now also beginning to offer an alternative to such modern materials as plastics. But it’s history goes much further back, Starting with 1,000 years ago, as caravans crossed Eurasia to transport silk from China to Europe; and at least as far back as 6,000 years, when silk was first used in funeral rituals. Today’s guest is Aarathi Prasad, author of “Silk: A World History.” She wrote a cultural and biological history from the origins and ancient routes of silk to the biologists who learned the secrets of silk-producing animals, manipulating the habitats and physiologies of moths, spiders, and mollusks. Because there is more than one silk, there is more than one story of silk. More than one road, more than one people who discovered it, and wove its threads.