The theory known as spontaneous generation held that complex, living organisms are generated by decaying organic substances. Mice might spontaneously appear in stored grain or maggots could spontaneously appear in meat.

According to Aristotle it was a readily observable truth that aphids arise from the dew which falls on plants, fleas from putrid matter, mice from dirty hay, crocodiles from logs rotting at the bottom of bodies of water, and so forth. In the 17th century these things started to be questioned.Sir Thomas Browne wrote a book called Pseudodoxia Epidemica. He subtitled it Enquiries into Very many Received Tenets, and Commonly Presumed Truths. He published it in 1646. He wrote it as an attack on false beliefs and "vulgar errors".  view more...