"...I saw the dying, the living, and the dead, lying indiscriminately upon the same floor, without anything between them and the cold earth, save a few miserable rags upon them. To point to any particular house as a proof of this would be a waste of time, as all were in the same state; and, not a single house out of 500 could boast of being free from death and fever..."– Irish artist James Mahoney, 1847
The blight that struck the potato crops in Ireland between 1845 and 1852 was caused by Phytophthora infestans, a fungus-like microorganism that attacks through the leaves. Using specimens of leaves from that time period, found in the Botanical State Collection in Munich and Kew Gardens in London, British scientists were able to extract DNA from the plants and sequence their genomes to track the spread of the pathogen. They discovered that the strain of P. infestans which devastated Ireland had diverged from the strain that originated in Mexico and spread to the rest of the Americas. It spread to Europe in the 1800s, but – unlike some of the strains which continue to affect crops to this day – died out in the early 1900s. More than 1 million people died as a result of the Irish potato famine and another million emigrated to England, America, and Australia. That amounted to as much as 25% of the population, from which Ireland (now consisting of Northern Ireland and the Republic of Ireland) has still not recovered.