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300 BCE
Aristotle thinks about spontaneous generation
Aristotle was one of the earliest known proponents of the theory of spontaneous generation, which held that small organisms could arise from non-living matter without the need for preexisting life. According to this theory, the appearance of these organisms was thought to be a natural process rather than the result of reproduction by living organisms. -
Redi's experiment
Redi, who was a scientist that believed that spontaneous generation is not real, conducted an experiment to challenge the concept of spontaneous generation. He placed meat into a jar and sealed it to demonstrate that flies did not appear inside. This disproved the idea that rotting meat was responsible for the appearance of flies, thus supporting Redi's belief that spontaneous generation was not a real phenomenon. -
John Needham
John Needham conducted an experiment to support spontaneous generation by boiling a broth to kill microorganisms and covering it to prevent new ones from entering. However, his results were not conclusive due to experimental issues, as microorganisms appeared. Later experiments by Spallanzani and Pasteur showed that spontaneous generation did not occur. -
Lazzaro Spallanzani
Spallanzani repeated Needham's experiment, but sealed the flask immediately after boiling. This challenged spontaneous generation as no microorganisms appeared. However, his findings were not widely accepted, and the theory persisted until Pasteur's experiments. -
Louis Pasteur (1)
Louis Pasteur played a crucial role in disproving the theory of spontaneous generation. He conducted an experiment using a flask with a uniquely designed S-shaped neck that allowed air to flow in, but prevented microorganisms from entering the broth. This design was essential in demonstrating that the idea of a "life force" creating living organisms was incorrect. When Pasteur observed that there was no bacterial growth in the broth, ... -
Louis Pasteur (2)
... he concluded that the theory of spontaneous generation was false, and that life only comes from pre-existing life. To confirm his theory, he tilted the flask, allowing the microorganisms from the air to come into contact with the broth. The broth then became contaminated, which confirmed his theory that life comes from other life. This experiment was a significant milestone in the history of science and helped establish the fundamental principle of biogenesis.