spontaneous generation Redi, Needham, Spallanzani, and Pasteur Spontaneous Generation • For much of history, people believed that animals could come from non-living sources. They thought: – Frogs developed from falling drops of rain – mice arose from sweaty underwear – and flies arose from decaying meat. • This is called abiogenesis • Also known as spontaneous generation • These ideas were followed because people simply accepted what they were told