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Francesco Redi
In 1668, Francesco Redi, an Italian, poet and physician, made the first scientific experiment to deny the spontaneous generation.
To prove he was telling the truth, made an experiment to test the spontaneous generation of maggots by placing fresh meat in each of two different hars. -
Redi's Experiment
Redi's Experiment was the first attack on spontaneous generation.
At that time, maggots appear spontaneously in rotting meat, so Redi believed that maggots developed from eggs laid by flies.
To test his hypothesis, he put meat in a variety of flasks. Some of them open to the air, some sealed, and the rest covered with gauze.
Maggots appeared only in open flasks because the flies could reach to the meat and lay their eggs there. He concluded that spontaneous generation didn't exist. -
Needham’s rebuttal
The hypotheses of spontaneous generation continued. In 1745, John Needham, proposed an experiment that he considered the definitive.
Boiling killed microorganisms, so he proposed to test whether or not microorganisms appeared spontaneously after boiling broth.
He boiled chicken broth, put it into a flask and waited until microorganisms grew.
He observed living microorganisms in the broth, concluding spontaneous generation was a fact. -
John Needham
In 1745, an English clergyman called John Needham claimed that spontaneous generation could occur and made an experiment that he considered the definitive.
After the experiment, Needham claimed victory for spontaneous generation. -
Criticism from Spallanzani
Lazzaro Spallanzani did an experiment that proved Needham's conclusions wrong.
First, he sealed flasks with chicken broth inside. Then, he boiled them for a long time. Later, he observe that the broth did not have any trace of life, but when he unsealed the flask, microorganisms fastly appear in the broth.
He concluded that spontaneous generation was false and microbes came from contaminated air. -
Lazzaro Spallanzani
Lazzaro Spallanzani, an Italian priest, did not agree with Needham’s
conclusions, so he performed hundreds of carefully executed experiments using heated broth, like Needham. -
Louis Pasteur
Spontaneous generation's theory was finally laid to rest in 1859 by the young French chemist, Louis Pasteur.
The French Academy of Sciences sponsored a contest for the best experiment either proving or disproving spontaneous generation. Pasteur's winning experiment was a variation of the methods of Needham and Spallanzani. -
Spontaneous generation to rest
Louis Pasteur re-create the experiment.
He boiled meat broth in a flask, heated the neck of the flask in a flame until it became pliable, and bent it into the shape of an S.
Air could enter the flask, but airborne microorganisms could not.
Any microorganisms grew, as Pasteur has expected but when he tilted the flask, the broth rapidly became cloudy with life.
Pasteur had both refuted the theory of spontaneous generation and demonstrated that microorganisms are everywhere.