You can chart the course of human progress in terms of how clean our clothing is. In early times people used animal skins, had no change of clothing, and had no soap. By Adam Smith's day soap had improved in quality, was produced industrially, and was becoming available to the common man. In fact, the Industrial Revolution, which is usually discussed in terms of iron, steam, and factories, was actually all about bringing products like soap and underwear — previously only available to the rich — to the common peasants. Only after WWII did electric automatic clothes washers displace hand-cranked...