Spontaneous generation is the belief that some life forms are created from non-living things. It was an accepted theory to explain the creation of living things since the times of the ancient Romans to the early nineteenth century, when people began to become more skeptical of this idea. By the 20 th century, spontaneous generation was known to be an incorrect theory. The reason it was known to be incorrect, primarily, was because of four scientists: Francesco Redi, John Needham, Lazzaro Spallanzani, and Louis Pasteur. Francesco Redi, in 1668, started the chain of experiments that would all add up to dissolve the theory of spontaneous generation. Redi was able to do this by doing a famous experiment involving meat and flies.

He covered a jar of meat so no flies could enter it and, after a few days, there were no flies. This experiment showed that flies were not created from meat. This, in turn, showed to other scientists that "larger" organisms were not created spontaneously. Redi's experiment was monumental because it was the first time spontaneous generation had been disproved by concrete evidence. Along with that, the experiment's result was a step for other scientists to build on in the future. Without Redi's findings, the process of proving spontaneous generation was a false theory could have been delayed drastically.

The next two scientists to make significant impacts on the theory of spontaneous generation were John Needham and Lazzaro Spallanzani. John Needham was a Scottish clergyman who, from 1745 to 1748, attempted to show that there was a life force in the molecules of all inorganic matter that caused spontaneous generation to occur. He went about doing by doing experiments which showed bacteria would form in soups. Seventeen years later, Italian biologist Lazzaro Spallanzani tried to disprove Needham's belief. Spallanzani went about this by doing three experiments. The first experiment was done by boiling soup for an hour, putting it in a flask, and then sealing off the flask.

The second experiment involved boiling soup for a few minutes, putting it in a flask, and sealing it of. The third experiment was done by boiling soup for an hour, putting it in a flask, and sealing the flask with a cork that let air in. Out of the three experiments, the first experiment was the only one which led to no bacteria forming. From these experiments, Spallanzani figured that an hour of boiling could kill the bacteria and bacteria came to substances through the air.

The result of Spallanzani's experiments was a debate between him and Needham over the process of boiling (sterilization) as a way of disproving spontaneous generation. While John Needham was a proponent of spontaneous generation, he was a significant figure in dissolving the belief of spontaneous generation. This was because his experiments led to Spallanzani doing his sterilization experiments. Spallanzani and Needham's arguments between each other were even more influential than their experiments because these arguments started the major debate between all scientists on the subject of spontaneous generation.

This debate between scientists then led to the experiment that completely disproved spontaneous generation by Louis Pasteur. Louis Pasteur was lured into doing this experiment by the Paris Academy of Sciences, which offered a prize to anyone who could create an experiment which resolved the spontaneous generation conflict. His experiment was done by putting soup in a flask and then putting cotton in the flask's neck. The cotton allowed air to pass to the soup, but not bacteria. After many days, bacteria were not present in the soup. Pasteur concluded that "there is no life force in air, and organisms do not arise by spontaneous generation" from the 'life force'.

Louis Pasteur was, by far, the most significant person in the effort to disprove spontaneous generation. Pasteur's efforts were so significant because his experiment closed the door on the possibility of spontaneous generation occurring. While there were still a fair amount of scientists that believed in spontaneous generation previous to the experiment, afterwards, there were barely any. Pasteur said, "Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment" and he was correct.