History of Spontaneous Generation Summarized: Videos & Practice Problems

Francesco Redi, an Italian scientist in the 1600s, was the first to challenge spontaneous generation. He conducted experiments showing that maggots on decaying meat came from fly eggs, not from the meat itself. By covering some jars of meat with gauze and leaving others open, he demonstrated that maggots only appeared in the open jars where flies could lay eggs. This experiment was crucial in disproving the idea that life could spontaneously arise from non-living matter, supporting the concept of biogenesis instead.

John Needham, an English scientist in the 1700s, conducted experiments that he believed supported spontaneous generation. He boiled broth, sealed it in flasks, and observed microbial growth, concluding that life could spontaneously arise. However, his experimental setup was flawed; he did not boil the broth long enough to kill all microbes, and his sealing method allowed contamination. These flaws led to incorrect conclusions, which were later corrected by other scientists like Lazaro Spallanzani.

Lazaro Spallanzani, an Italian scientist, improved upon John Needham's experiments by addressing their flaws. He boiled the broth for a longer time to ensure all microbes were killed and sealed the flasks by melting the glass, preventing contamination. Spallanzani's experiments showed no microbial growth, providing strong evidence against spontaneous generation and supporting biogenesis. However, some scientists argued that he excluded a vital air component necessary for spontaneous generation.

Louis Pasteur's swan neck flask experiment was pivotal in disproving spontaneous generation. He designed flasks with long, curved necks that allowed air to enter but trapped dust and microbes in the bend. When he boiled the broth in these flasks, no microbial growth occurred, demonstrating that microbes did not spontaneously generate but came from external contamination. This experiment provided strong evidence for biogenesis, showing that life arises from existing life, not from non-living matter.

John Tyndall, an English physicist, played a crucial role in the history of spontaneous generation by explaining why some scientists could not replicate Louis Pasteur's results. Tyndall discovered that certain microbes, such as endospores, are heat-resistant and can survive boiling. This explained why some broths still showed microbial growth despite boiling. Tyndall's findings supported Pasteur's conclusions and further disproved spontaneous generation, reinforcing the concept of biogenesis.