No matter how many walls are constructed and checkpoints set up, migration is an ancient response to the need to find new sources for shelter, safety and food. And climate change has often been at the root of these mass movements. Science journalist Sonia Shah joins host Krys Boyd to talk about why global movement is actually a hopeful signal, bringing with it diversity and help for ecosystems. Her new book is called “The Next Great Migration: The Beauty and Terror of Life on the Move.”