Bill Clinton returned to his alma mater thirty-seven years after graduating to address the Yale class of 2010. After playfully admiring the graduates' outlandish hats and noting that if he hadn't come to Yale he never would have met Hillary, Clinton turned serious. He argued that despite living in the most interesting time in human history — with technology connecting the world and the genome revealing that all humans are 99.5% genetically identical — three fundamental problems threatened everything. Inequality (half the world living on less than two dollars a day), instability (from terrorism to financial crises spreading across borders), and unsustainability (climate change accelerating beyond what the planet can bear). He told the graduates that addressing these three interlinked challenges would be the defining work of their generation.