Biological immunity as we know it does not exist until the late nineteenth century. Nor does the premise that organisms defend themselves at the cellular or molecular levels. For nearly two thousand years "immunity," a legal concept invented in ancient Rome, serves almost exclusively political and juridical ends. "Self-defense" also originates in a juridico-political context; it emerges in the mid-seventeenth century, during the English Civil War, when Thomas Hobbes defines it as the first "natural right." In the 1880s and 1890s, biomedicine fuses these two political precepts into one,...