It took humankind 1800 years to get from a global population of about 200 million to 1 billion. But it only took us 200 years to go from a billion to 7 billion.  Most students of population agree that the planet cannot support current rates of population growth for much longer. This week Sea Change Radio begins a two-week series on population. Today we spend the whole show talking with Paul R. Ehrlich, author of the environmental classic, The Population Bomb and one of the foremost scholars on the subject. Dr. Ehrlich talks with host Alex Wise about the optimism of that book, the events and policies that subdued that optimism, and the ideas that drive his most recent tome, Humanity on a Tightrope. We ask Dr. Ehrlich about what needs to happen now to ensure the sustainability of the planet and the human race and about why controlling population growth is a centerpiece of the solution he envisions. He also shares his views on economics, immigration, US politics, and his personal choice to have only one child.