The fact that so many animals migrate — sometimes thousands of miles — has puzzled people over the ages. Why do they take such risky journeys? Conservation biologist David Wilcove studies migration, and he says the scale of migration is staggering.

Valmont Layne grew up under apartheid in South Africa. Music, along with protest movements, radicalized him. He tells Anne and Steve that South African jazz became a musical current that’s traveled across oceans, spreading ideas about freedom.

Political repression and censorship forced a generation of Black jazz musicians out of South Africa and into clubs in Europe and the US. But jazz critic Gwen Ansell says some musicians remained, and they left a legacy of unforgettable music.