Spontaneous generation was once believed to be the mechanism by which organisms could originate directly from non-living matter. The process is also known as abiogenesis, from the Greek roots a-, not, bio-, life, and genesis, origin.

Early examples of this theory included the generation of maggots from rotting meat, mice from dirty hay, and lice from sweat. The first of these was debunked by a simple experiment carried out by the Italian scientist Francesco Redi in 1668.