At the turn of the century and the millennium, Science carried a series of essays titled Pathways of Discovery. An extremely readable and characteristically eloquent essay on Infectious History still holds a place, albeit indistinct and receding, in my memory. The author, Joshua Lederberg, was one of the most influential figures of 20th century biology and a writer of rare scholarship. In his essay, Lederberg traces the history of the relationships between men and microbes; a long history of