IRELAND: An Gorta Mór ("The Great Hunger"), as the 1840s famine is known in Irish, led to the deaths of 1.5 million people and the emigration of two million more. The famine was caused by Phytophthora infestans, a microorganism that causes the plant disease known as potato late blight. Researchers have now extracted genetic data for the pathogen from ground-up, rotten potato samples from 19th-century experiments. They found that the same lineage of P. infestans was responsible for another epidemic 30 years later, and are now sequencing the whole genome to see how it changed over time. —Samir S. Patel