Spontaneous Generation

Spontaneous Generation, or abiogenesis, ancient theory holding that certain lower forms of life, especially the insects, reproduce by physicochemical agencies from inorganic substances. This view went uncontradicted until after the middle of the 17th century, when the Italian physician and poet Francesco Redi disproved (1668) the prevailing notion that the maggots of flies were generated in putrefying meat exposed to air. In 1768, the Italian naturalist Lazzaro Spallanzani further showed that microorganism-containing solutions that were boiled and then sealed off would remain free of microorganisms thereafter; and in 1836 the German naturalist Theodor Schwann provided additional proof with still more meticulous experiments of this nature.

The next step was taken by the French chemist and microbiologist Louis Pasteur, who summarized his findings in On the Organized Particles Existing in the Air (1862). On sowing these particles in suitable sterilized nutrient broths, he found that after a day or two the broth teemed with living microorganisms. Organisms such as these were shown by the German botanist Ferdinand Julius Cohn to be plants (a classification that held until the 19th century), and he named them bacteria. Finally, the British physicist John Tyndall showed (1869), by passing a beam of light through the air in a box, that whenever dust was present putrefaction eventually occurred; when dust was absent, putrefaction did not occur. These experiments resulted in the demise of the theory of spontaneous generation.

See also Evolution; Exobiology; Life.