Life expectancy history: Public health and medical advances that lead to long lives. - Slate Magazine: "The vast majority of deaths before the mid-20th century were caused by microbes—bacteria, amoebas, protozoans, or viruses that ruled the Earth and to a lesser extent still do. It’s not always clear which microbes get the credit for which kills. Bills of mortality (lists of deaths by causes) were kept in London starting in the 1600s and in certain North American cities and parishes starting in the 1700s. At the time, people thought fevers were spread by miasmas (bad air) and the treatment of choice for pretty much everything was blood-letting."