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Spontaneous generation is an obsolete theory regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence. The original theory is attributed to Aristotle, and it held sway for two millennia. It is generally accepted to have been ultimately disproven in the 19th Century by the experiments of Louis Pasteur, expanding upon the experiments of other scientists before him. Ultimately, it was succeeded by germ theory and cell theory.

The disproof of ongoing spontaneous generation is no longer controversial, now that the life cycles of maggots and other pests have been well documented. However, the question of abiogenesis, how living things originally arose from non-living material, remains relevant today.

Ancient beliefs

Aristotle lay the foundations of Western natural philosophy. In his book, The History of Animals, he stated in no uncertain terms:

Now there is one property that animals are found to have in common with plants. For some plants are generated from the seed of plants, whilst other plants are self-generated through the formation of some elemental principle similar to a seed; and of these latter plants some derive their nutriment from the ground, whilst others grow inside other plants, as is mentioned, by the way, in my treatise on Botany. So with animals, some spring from parent animals according to their kind, whilst others grow spontaneously and not from kindred stock; and of these instances of spontaneous generation some come from putrefying earth or vegetable matter, as is the case with a number of insects, while others are spontaneously generated in the inside of animals out of the secretions of their several organs.

— Aristotle, History of Animals, Book V, Part 1

Examples of the original theory, put forth by Aristotle, included the generation of maggots from rotting meat, mice from dirty hay, birds from trees, and lice from sweat.

According to Aristotle's theory, living things came forth from nonliving things because the nonliving material contained pneuma, or "vital heat". The creature generated was dependent on the proportions of this pneuma and the five elements he believed comprised all matter.

Scientific method

Ancient beliefs were subjected to testing. Francesco Redi challenged the idea that maggots arose spontaneously from rotting meat. In the first major experiment to challenge spontaneous generation, he placed meat in a variety of sealed, open, and partially covered containers. Realizing that the sealed containers were deprived of air, he used "fine Naples veil", and observed no worm on the meat, but they appeared on the cloth.

In 1745, John Needham performed a series of experiments on boiled broths. Believing that boiling would kill all living things, he showed that when sealed right after boiling, the broths would cloud, allowing the belief in spontaneous generation to persist.

Lazarro Spallanzani modified the Needham experiment in 1768, attempting to exclude the possibility of introducing a contaminating factor between boiling and sealing. His technique involved boiling the broth in a sealed container with the air partially evacuated to prevent explosions. Although he did not see growth, the exclusion of air left the question of whether air was an essential factor in spontaneous generation.

In 1837, Charles Cagniard de la Tour, a physicist, and Theodor Schwann, one of the founders of cell theory published their independent discovery of yeast in alcoholic fermentation, in studies using the microscope.

Louis Pasteur's 1859 experiment put the question to rest. He boiled a meat broth in a flask that had a long neck which was bent to prevent any particles from falling in. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth became clouded, quickly.

References

1. Aristotle (1910) . "Book V". The History of Animals. translated by D'Arcy Wentworth Thompson. Oxford: Clarendon Press. Retrieved 2008-12-20. {{cite book}}: External link in |chapterurl= (help); Unknown parameter |chapterurl= ignored (|chapter-url= suggested) (help)
2. Wilkins, John S. (2004). "Spontaneous Generation and the Origin of Life" (HTML). The Talk.Origins Archive. Retrieved 3 December 2008. {{cite web}}: Unknown parameter |month= ignored (help)
3. ^ Russell Levine (1999). "The Slow Death of Spontaneous Generation (1668-1859)". Washington, D.C.: National Health Museum. Retrieved 2008-12-19. {{cite web}}: Unknown parameter |coauthors= ignored (|author= suggested) (help)
4. Francesco Redi of Arezzo (1909) . Mab Bigelow (translator) (ed.). Experiments on the Generation of Insects. Chicago: Open Court. Retrieved 2008-12-19. {{cite book}}: |editor= has generic name (help)

• Obsolete biological theories