Who disproved the theory of spontaneous generation?

Louis Pasteur disproved the theory of spontaneous generation. The theory claimed that living organisms could regularly arise from nonliving material, such as maggots appearing in decaying meat or microorganisms emerging in broth. Earlier experiments by Francesco Redi and Lazzaro Spallanzani had challenged parts of the idea, but the debate continued into the nineteenth century.

In the late 1850s and early 1860s, Pasteur boiled nutrient broth in glass flasks with long, curved “swan necks.” Air could enter, but dust and microorganisms became trapped in the bends, so the broth remained clear. When a flask was tilted or its neck was broken, contaminated particles reached the broth and microbial growth appeared. This showed that the organisms came from the environment rather than forming spontaneously inside the liquid.

John Tyndall later supplied important additional evidence by studying heat-resistant microbial spores, so he is sometimes mentioned in detailed historical accounts. Nevertheless, Pasteur is the standard canonical answer because his swan-neck-flask experiments decisively changed scientific opinion and helped establish the principle of biogenesis.