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Redi’s experiment
Francesco Redi demonstrated that maggots in meat did not arise spontaneously, but from eggs laid by flies. In his experiment: Open jars: Maggots appeared in the meat.
Sealed jars: No maggots.
Jars covered with gauze: No maggots in the meat, but maggots in the gauze. These results confirmed Redi’s hypothesis and provided strong evidence against spontaneous generation, demonstrating that maggots come from flies, not from the meat itself. -
Needham’s rebuttal
Although Redi had shown that worms don't arise spontaneously, many still believed in spontaneous generation, especially for microorganisms. In 1745, Needham attempted to prove this by doing this experiment. He briefly heated the broth, cooled it, and sealed it in jars. Finding microorganisms in the sealed broth, he claimed that life could be generated without the need for previous organisms. After a while, he observed microorganisms in the broth and concluded that they could arise spontaneously. -
Criticism from Spallanzani
Lazzaro Spallanzani, in the 18th century, refuted spontaneous generation by boiling broth longer than Needham and sealing the jars tightly before cooling. He observed no microorganisms in the sealed jars, concluding that they only appeared if introduced from the external environment. This supported the idea that life originates from pre-existing organisms. Spallanzani argued that Needham's heating was insufficient to eliminate all microorganisms. -
Pasteur puts spontaneous generation to rest
Louis Pasteur disproved spontaneous generation using swan-neck flasks. He boiled nutrient-rich broth in flasks with S-shaped necks, which allowed air but trapped particles. For a year, no microorganisms appeared. When he broke the neck or tilted the flask to expose the broth to airborne particles, microorganisms grew within days. Pasteur concluded that life arises from existing organisms in the air, not from a "life force," solidifying the concept of biogenesis.