Three billion people on earth live on less than two dollars a day. A relative handful of us fare astronomically better. How do economists account for global “haves” and “have-nots”? Roberto Rigobon attributes a vast income inequality across countries to four connecting factors: luck, geography, quality of institutions, and quality of policies. If a country lies close to the 50th parallel, its citizens’ average income is six times greater than that of an equatorial country. Heat takes a toll on nation-building. Take Caribbean and Latin American countries, which experienced a wave of malaria in the 1500’s. Spanish colonists preferred to extract resources and send them home, rather than risk death by staying. Those nations developed impoverished economies and institutions that continue today. Colonists moved to cooler climes settled down, invested in the new world, and created enduring social structures. Rigobon can’t recommend a single, economic, or political doctrine to help a struggling nation achieve prosperity. “The set of rules depends on a country’s culture, history and religion…. In the end the only sustainable regime is democracy, freedom of speech, and the rule of law, but how we get there isn’t irrelevant.” Rigobon encourages developing nations to embrace social and political conflict as “an opportunity to improve.”