ABSTRACT
Ahundred years ago, at the dawning of the twentieth century, the world was very different from what it is now. People considered it the height of modernity to be able to travel across a continent by spending days on a coalpowered train. Life expectancy was barely half of what it is now, and diseases like diphtheria, pneumonia, and smallpox were major killers. Today, we routinely fly coast to coast in a matter of hours, and virtually the only smallpox virus left on the planet is kept under strict containment at a scientific laboratory, in case we need it to develop vaccines to combat it in the future.
