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The first theories for spontaneous generation was compiled and synthesized by Aristotle, who gathered many different claims from previous philosophers.
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During the 17th century, recipes to "create" life were formulated. This was done to prove that organic life could arise from inorganic matter – for example, rotting meat gave "birth" to maggots.
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Francesco Redi was the first person to publicly oppose the idea of spontaneous generation through his famous meat experiment. During this experiment, he placed meat in three seperate jars. He left the first jar uncovered, and placed gauze for one and a cork for the other. Maggots appeared in the meat of the open jar, because flies were able to enter. However, for the other two jars, which prevented flies from entering, the meat, the meat was found maggot-free.
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John Needham created another experiment to prove the existance of spontaneous generation, and he did so through the boiling of chicken broth. He began by boiling chicken broth, then placing it into a sealed flask. He reasoned that since boiling kills all micro-organisms, the broth in the flask would be inorganic. After a few days, he observed the growth of micro-organisms in the broth, and concluded that spontaneous generation was real.
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Lazzaro Spallanzani was an Italian Priest who suggested that the micro-organisms could have entered Needham's broth while it was being placed into the flask. Thus, he modified the experiment by first placing the chicken broth into a sealed flask, and then drawing out air to create a vacuum before boiling the broth. After a few days, no micro-organisms had grown; however, critics claim that he had only proved that spontaneous generation could not occur without air.
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In 1859, the French Academy of Sciences sponsered a contest to dis/prove spontaneous generation. The winner, Louis Pasteur, created an experiment based off both Needham and Spallanzani's expierments. He first boiled the broth in a flask, then heated the neck of the flask to bend it into the shape of an S. This way, air could enter the flask but not airborne micro-organisms. After a while, it was observed that no micro-organisms grew, finally ending the age-long question of spontaneous genera
