The first wave of the second plague, which lasted from 1347 to 1353, is what we think of as the Black Death, although that term was not used at the time. During this first wave, driven by a favorable environment of densely packed towns and cities and substantial poverty, as much as half of the population of Europe was wiped out. This force was so powerful that it even acted as a selection pressure, changing the course of human evolution. As we will see in chapter 8, many people may have genetic features today that reflect the fact that their ancestors were the ones who survived.
