The United Nations wants more people to appreciate the potato's potential to fight world hunger. People in many parts of the world indulge in the curious practice of eating dirt, also known as geophagy, but why they do so has remained something of a mystery. Still with us: Two pre-modern ailments are making a comeback. Unintended victims of Gates Foundation generosity: Donations to fight AIDS, TB and malaria in Africa have inadvertently put many of those with other basic healthcare needs at risk. A review of Bad Samaritans: Rich Nations, Poor Policies and the Threat to the Developing World by Ha-Joon Chang. Tim Harford on measuring the effectiveness of foreign aid. Young economists show big goals such as curbing corruption can be addressed in little, randomised and quantifiable steps.