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Spontaneous generation theory is an archaic scientific theory which stated that living organisms could arise from nonliving matter and that such a process was regular in nature. It also explained the origin of life from the nonliving subjects. According to that theory, a piece of bread and cheese wrapped and left in a corner could give rise to mice in a few weeks, or maggots could rise from dead flesh.
The hypothesis was designed by Aristotle on the basis of previous work of natural philosophers and the theory held its place for two millenniums. Francesco Redi and Lazzaro Spallanzani then challenged this theory in the 17th and 18th centuries, but it was still not discredited. It was not until the work of Louis Pasteur and John Tyndall in the 19th century that this theory was finally disproved.
The theory lines up with the theory of origin of life, which states the process of abiogenesis. Abiogenesis is the natural process of creation of simple organic compounds from nonliving matter. The term equivocal generation, also called heterogenesis, describes the theory of spontaneous generation. According to equivocal generation, one life arises from another unrelated life form.
Aristotle’s Work
According to Aristotle, every living being is made up of a compound of matter and form. In his sexual theory of reproduction, he stated that male’s semen was efficient cause that passed down characteristics to female matter (menstrual blood), and gave rise to its offspring. He believed that the male semen and female matter were refinements that were produced by bodies as a result of their proportions of heat, ingested food and were a byproduct of the elements earth and water. Yet, he believed that creatures arose from spontaneous generation and not sexual reproduction.
Analogous to his sexual reproduction theory, he said that non living matter just like seminal fluid had ‘pneuma’ or ‘vital heat’ that endowed the subtances with vital properties. He came to the conclusion that whether a life form arose from sexual reproduction or spontaneous generation, they were a result of interaction between vital heat and elemental matter.
Early Experiments
Franceso Redi
Franceso Redi was an Italian naturalist who challenged the ancient belief of spontaneous generation of maggots on decaying meat in 1668. He believed that maggots could be prevented if flies were not allowed direct contact with the meat. He designed an experiment where he put pieces of meat in six different containers. He covered two of them with gauze, two tightly sealed with corks and left the remaining two open in the air. His hypothesis came true as it was observed that there were no maggots in the covered (with gauze and cork) containers but maggots were observed in the open container. He came to the conclusion that flies were able to lay their eggs on the open piece of meat and that the maggots were their offspring who grew on flesh.
Pier Antonio Micheli
Pier Antonio Micheli, an Italian botanist, performed another experiment in 1729 where he placed fungal spores on a slice of melon and observed that the same was produced on the melon slice. He concluded that the new spores definitely did not arise from spontaneous generation.
John Needham
John Needham, an English biologist, did yet another experiment in 1745 with boiled broths. He infused a broth by mixing plant and animal matter and boiled it in the belief that it would kill all the microorganisms. He sealed the broth and left it for a few days. He observed that the broth had become cloudy and that it has microscopic organisms in it. He reiterated the spontaneous generation theory and many of his peers believed him. However, in reality, the broth was not boiled vigorously so as to kill all the microorganisms.
Lazzaro Spallanzani
Lazzaro Spallanzani, an Italian biologist, reattempted Needham’s experiment in 1768. He took animal and plant matter-infused broths and boiled them vigorously. He kept one of the jars sealed and left the other one open to the air. According to his observations, the sealed jar was clear and did not have any growth. He then concluded that air was the force that was introducing microbes into the flask.
By this time, there was increased skepticism among scientists about the spontaneous generation theory.
Disproving the Theory
Louis Pasteur
In 1859, Louis Pasteur, a French microbiologist conducted another broth experiment that settled the question of spontaneous generation once and for all. He took swan flasks that had twisted necks for the experiment and boiled meat broth in it. The design of the flask was such that it allowed exchange or air from outside to inside but prevented the entry of microorganisms. If any microbes were to enter the flask they would get caught in the twisted neck of the flask. The broth remained clear for a long amount of time as long as the flask was kept intact. Once the flask was turned, which led to entry of microbes into the broth, it became cloudy.
John Tyndall
John Tyndall, an Irish physicist, advanced the work of Louis Pasteur and finally the theory of spontaneous generation was disproved. Not much is known about Tyndall’s experiment on spontaneous generation.
In 1862, the French Academy of Sciences, announced a prize for the scientists who shed new light on the spontaneous generation controversy and appointed a jury to decide the winner. Louis pasteur was awarded the Alhumbert Prize from the Paris Academy of Sciences for his work that totally threw away the concept of spontaneous generation. 1n 1864, Pasteur was quoted saying in a lecture: “Omne vivum ex vivo” (“Life only comes from life”). Pasteur and other scientists started to use the word biogenesis for the origin of life which again meant that life comes only from another life.
This sums up the theory of spontaneous generation. Keep visiting BYJU’S Biology for more interesting topics.
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