Synthesis document 3 - Spontaneous generation

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  • 1668 – Francesco Redi’s Experiment

    1668 – Francesco Redi’s Experiment
    “If flies can’t reach the meat, no larvae will appear because they come from fly eggs, not the meat itself.”
    Experiment: Redi placed meat in three jars: one open (flies could access), one sealed, and one covered with gauze.
    Conclusion: Maggots appeared only in the jars where flies could access the meat, supporting the idea that life (maggots) comes from other life (flies), not spontaneously from meat.
    Limitations: Redi didn’t have tools like microscopes, so he couldn't address microorganisms.

  • 1745 – John Needham’s Experiment

    1745 – John Needham’s Experiment
    Experiment: Needham boiled broth to kill microorganisms, then sealed it in flasks. After a while, he observed microbial growth.
    Conclusion: Needham concluded that spontaneous generation occurred because microorganisms appeared in the sealed broth.
    Flaws: The broth may not have been heated enough to kill all microorganisms, or the sealing might have been imperfect, allowing new microorganisms to enter.

  • 1768 – Lazzaro Spallanzani’s Experiment

    1768 – Lazzaro Spallanzani’s Experiment
    Experiment: Spallanzani did the same experiment as Needham, but the difference is that he boiled the broth in the flasks while they were already properly sealed, to prevent from contamination. After a while, no life appeared in the sealed flasks.
    Conclusion: Life in the broth came from air contamination, not from spontaneous generation.
    Criticism: Supporters of spontaneous generation argued that Spallanzani’s boiling process removed a "life force" in the air, preventing spontaneous generation.

  • 1859 – Louis Pasteur’s Experiment

    1859 – Louis Pasteur’s Experiment
    Hypothesis: “Life comes from other life, not from non-living matter.”
    Experiment: Pasteur used flasks with S-shaped necks. He boiled broth inside the flask and kept it exposed to air, but microorganisms couldn’t reach the broth due to the design of the neck. When he broke the neck or tilted the flask, microorganisms appeared.
    Conclusion: Pasteur proved that microorganisms came from the air, not from spontaneous generation. His experiment is a key demonstration that life comes only from life.