Abstract
The origin of life has been of enduring interest. Aristotle strongly advocated "spontaneous generation" arguing that it was observed fact that some animals spring from putrid water, that plant lice arise from the dew that falls on plants, that fleas emerge from decaying matter, etc. With the invention of the microscope previously invisible life forms became further candidates to emerge from nonlife. Skeptics had little on which to base their claims until Italian physician Francesco Redi experimentally demonstrated (1668) that maggots did not appear in meat in which flies were prevented from laying their eggs by wire screens. Later workers gradually demonstrated that the higher animals were not spontaneously generated from the nonliving; microorganisms--the monads and bacteria--were another matter.