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The belief in spontaneous generation was widespread, rooted in ancient Greek philosophy. Aristotle suggested life could arise spontaneously under specific conditions, such as decaying organic matter producing small animals. -
Person: Francesco Redi (1626–1697) An Italian physician and naturalist, Redi is considered one of the first experimental biologists. He questioned the belief in spontaneous generation for larger organisms.
Experiment: Redi placed meat in three types of jars: open, sealed, and covered with gauze. Maggots appeared only in the open jar where flies could lay eggs.
Impact:
He concluded maggots came from flies, not spontaneous generation. -
Person: John Needham (1713–1781) An English biologist and priest, Needham supported spontaneous generation and aimed to prove it scientifically.
Experiment: Needham boiled meat broth, sealed it in flasks, and observed microbial growth. He argued this proved microorganisms spontaneously generated from the broth's "vital force."
Impact:
His experiment temporarily revived belief in spontaneous generation, though his methods were later criticized. -
Lazzaro Spallanzani (1765) Conducted experiments to refute John Needham’s claim of spontaneous generation. He boiled broth for a longer time and sealed the flasks more securely. No microbial growth occurred in the sealed flasks, but when the seal was broken, microbes appeared. Spallanzani concluded that microorganisms came from the air, not the broth. Critics argued his airtight seals blocked the "vital force," leaving the debate unresolved until Pasteur's experiments. -
Pasteur (1822- 1895) used swan-neck flasks containing broth. The flasks allowed air to enter but trapped dust and microorganisms in the neck. The broth remained sterile unless the flask was tilted, exposing it to contaminants.
Impact:
Pasteur conclusively disproved spontaneous generation, proving that microorganisms originate from existing microbes in the environment.