The idea of the tree of life appears in many of the world's religions, and it appears, famously, in science, with Darwin's famous tree of life, where species evolve over millions of years from a common ancestor in the trunk to new species in the branches. But while Darwin's tree of life endures in textbooks, t-shirts and tattoos, science has moved on. And the tree of life has become more of a tangle. We will speak with David Quammen about his new book "The Tangled Tree: A Radical New History of Life", and with Julie Dunning Hotopp, who studies how...