Biology

Ancient Beliefs (Pre-1600s)

1600

People believed in spontaneous generation based on observations of life forms (e.g., maggots in rotting meat). Philosophical and religious ideas supported this belief.

francesco redi

1668

Francesco Redi, an Italian physician, questioned the idea of spontaneous generation. Redi believed that maggots came from the eggs that were laid by flies so he put meat in various jars and sealed a few and left a few open. As he expected, only the jars that were open to air had maggots in it. This proved his theory because when the jars are sealed, flies were unable to lay eggs on the meat so there were no maggots.

John Needham

Jan 1, 1744

John Needham conducted an experiment to boil chicken broth to prove spontaneous generation. When he boiled chicken broth and put it in a sealed jar and microorganisms grew. He claimed this supported spontaneous generation, though his methods were flawed, as the heating might not have been sufficient to eliminate all microorganisms.

Lazzaro Spallanzani

Apr 1, 1745

Lazzaro Spallanzani, an Italian priest, improved on Needham’s experiment. He boiled broth for a longer time and sealed the flasks completely. No microorganisms appeared unless the seal was broken, proving contamination came from the air. Critics argued that air’s “vital force” had been removed in the process.

Louis Pasteur

1849

A French chemist Pasteur proved the spontaneous generation theory wrong. He performed a combined experiment of Needham’s and Spallazani’s. He boiled meat in a flask and heated the neck of the flask and bent it to an S shape. This allowed air to go into the flask but does not allow air borne microorganisms because they will settle on the S. Since no microorganisms grew, Pasteur proved the spontaneous generation theory wrong and also demonstrated microorganisms are everywhere.