Ever since man took to the battlefield, biology has played a significant role-both unintentionally and intentionally-in conflict. Prior to the discovery of the germ theory of disease, most combat deaths were the result of infections. And even before that understanding, biology was used in an offensive role. An early example was the Tatars' hurling of plague victims' bodies over the wall of the Crimean city of Kaffa in 1346, which probably helped spread the Black Death. Despite various treaties and protocols, offensive biological weapons use has continued to this day, with the anthrax attacks...