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400 BCE
Aristotle Establishes Belief of Spontaneous Generation
Aristotle claims that complex living organisms come from decaying substances based on his observations -
Belief Begins to be Questioned
In the 17th century Sir Thomas Browne writes a book called Pseudodoxia Epidemica, in which he attacks false beliefs and "vulgar errors". Other scientists doubt his conclusions, including Alexander Ross, who wrote: "To question [spontaneous generation] is to question reason, sense and experience". -
The Cell is Discovered
Robert Hooke discovers and names the cell while observing cork samples. He publishes the first drawings of a microorganism in 1665. -
Franceso Redi First to Disprove Spontaneous Generation
The Italian scientist Francesco Redi conducts an experiment where he proved that no maggots appeared in meat when flies were prevented from laying eggs. The alternative would be that every living thing comes from a pre-existing living thing. -
Interest in Microscopic World Sparked Again
Anthony van Leeuwenhoek uses his advanced lenses to discover microorganisms, most likely protozoa and bacteria. This stirs up curiosity in the microscopic world and eventually leads to cell theory. -
John Needham's Experiment Challenges Redi
John Needham, a British clergyman and biologist, conducts a conflicting experiment and reports living organisms inside a broth days after it had been heated to kill any life and sealed in a bottle. In reality, the broth hadn't been heated enough to kill everything inside the bottle. -
Lazzaro Spallanzani's Experiment Further Disproves Spontaneous Generation
Lazzaro Spallanzani, also an Italian scientist, looked at Redi's and Needham's findings and conducted his own experiment using two bottles, one sealed and one unsealed, that he boiled broth in. The sealed bottle had no life in it afterwards, proving that microbes came from the air and could be killed by boiling. Other scientists still insisted that spontaneous generation required air, which the sealed bottle didn't have access to. -
Louis Pasteur Disproves Spontaneous Generation
A French scientist called Louis Pasteur performed a careful experiment combining Redi and Needham's design, including a system open to air. Pasteur proved that organisms such as bacteria and fungi do not appear in nutrient-rich media of their own accord in non-living material, thus supporting cell theory.
