For the third time in 20 years, the United Nations has convened a global summit to discuss what many believe is the world’s most pressing problem: burgeoning population and its connection to human development. The world’s population has grown by more than a billion since the first conference in 1974, but for those attending this year’s conference in Cairo, there’s strong disagreement over what those numbers mean . . . and what should be done to create a sustainable human society. Host Steve Curwood reports.