Spontaneous Generation Theory – Concept and refutation

We explain what the Spontaneous Generation Theory is, what thinkers supported it and how it was refuted.

spontaneous generation theory
According to this theory, living things could arise from decomposing matter.

What is the theory of spontaneous generation?

The Theory of Spontaneous Generation was the name given to the belief that certain forms of plant and animal life arose automatically, spontaneous, from organic matter, inorganic matter or some combination of both.

This theory was in force for many centuries, since Antiquity. Although it is a hypothesis that could never be scientifically proven, many believed to verify it by direct observation.

Aristotle, the Greek philosopher, believed in this theory. It was also accepted and supported by 17th and 18th century thinkers such as Sir Francis Bacon, René Descartes, and Isaac Newton, who were unaware of the world of microbiology. It applied to small creatures kept by pests or parasites, such as flies, lice, ticks, and even mice.

The belief was that if the correct items (say: sweaty underwear and wheat) were left in a container, after some time some kind of animals (say: mice) would be found in their place.

This theory about the origin of life did not contradict conventional reproduction, since the creatures obtained by spontaneous generation were as perfect and identical as those born from sexual reproduction.

In this way, it could be sustained that in the decomposed meat, the excrement or the very entrails of the human being, various forms of life were given by spontaneous generation, instead of thinking that they had somehow gotten there.

Refutation of the Theory

theory spontaneous generation experiment pasteur science
Louis Pasteur designed an experiment to prevent the entry of microorganisms.

The theory of spontaneous generation was refuted through three specific experiments:

  • Redi’s experiment (1668). Carried out by Francesco Redi, an Italian doctor, who doubted that insects could arise spontaneously from putrefaction, and assumed that at some point some adult insect must lay eggs or larvae on decomposing matter. To verify this, he placed three pieces of meat in three different containers: one of them open and the other two sealed with gauze that allowed air to enter the jar but not the adult flies. After time, there were worms in the exposed meat and not in the sealed ones, although they did find fly eggs on the gauze.
  • Spallanzani’s experiment (1769). Later developed by the Catholic priest and naturalist Lázaro Spallanzani, it was a kind of prelude to pasteurization. The Italian placed meat broth in two containers, after having heated them to a temperature that would kill the existing microorganisms and having sealed it hermetically in the container. Thus he showed that microorganisms are not born spontaneously from matter, but come from other microorganisms.
  • Pasteur’s experiment (1861). Developed by the Frenchman Louis Pasteur, father of the food preservation technique known as pasteurization, it consisted in the introduction of meat broth into two long, curved-mouth distillation bottles (in the shape of an “S), which gradually became finer as it rises. The shape of the tube allowed air to enter, but made the microorganisms stay in the lower part of the container, without accessing the meat. Thus, he heated the broth until it was sterilized and simply waited: after several days, there were no signs of decomposition, after which Pasteur proceeded to cut the mouth of the container and there, after a short time, decomposition did occur, thus demonstrating that the microorganisms they came from other microorganisms and that, in general, all life forms come from another life form that precedes it.

It may interest you: Decomposing organisms