Human history is a long arc of progress. Thanks to technological innovation, we've never lived longer or healthier. But the distribution of that progress is uneven. According to the World Bank, global inequality is rising for the first time in decades, while even within developed nations, gaps between the rich and poor are expanding. So what drives progress and its unequal distribution? Economist Oded Galor's book "The Journey of Humanity" explores these questions. He joined us for Perspective.