Spontaneous Generation Definition

Spontaneous generation is an incorrect and obsolete hypothesis about the possibility of life forms being able to emerge from non-living things.

Spontaneous Generation Theory

The theory of spontaneous generation, first comprehensively posited by Aristotle in his book ”On the Generation of Animals” around 350 B.C., aims to explain the seemingly sudden emergence of organisms such as rats, flies and maggots within rotting meat and other decomposable items. The theory suggests that organisms do not descend from other organisms or from a parent, and only require that certain conditions in their environment be fulfilled in order for creation to occur.

Aristotle theorized that non-living matter contained a “vital heat” called pneuma—the concept of a “breath of life” and translated later as “anima” meaning “soul” in Latin—and a combination of the four elements believed to make up all life: earth, air, fire and water.

He suggested that animals and plants could arise from earth and liquid, because there was “vital heat” within all air, there is air in water, and there is water in earth, meaning there is “vital heat” or “soul” within everything.

His explanation of the spontaneous generation was as follows:

“… living things form quickly whenever this air and vital heat are enclosed in anything. When they are so enclosed, the corporeal liquids being heated, there arises as it were a frothy bubble. Whether what is forming is to be more or less honorable in kind depends on the embracing of the psychical principle; this again depends on the medium in which the generation takes place and the material which is included.”

Examples of Spontaneous Generation


One of the first accounts relating to spontaneous generation was by the Roman poet Virgil. He described, as a recipe, the process in which one could make synthetic bees.

The readers were instructed to beat a bovine calf to death, block up its mouth and nose, before leaving the carcass on a bed of cinnamon sticks and thyme.

He noted that creatures would magically appear “first voide of limbs, but soon awhir with wings”—presumably this is referring to maggots, which subsequently develop in to bees.

Virgil called the process described in the recipe “Bougonia”.

Spontaneous Generation of Mice

The “recipe” for making a mouse requires that sweaty underwear should be placed over an open-mouth jar containing husks of wheat inside for around 21 days.

A simple explanation: mice like to eat wheat and, with ease of entering a jar and finding a dark and safe space, would most likely to find themselves at home and have a few offspring in the new nest.


The European chemist Jean Baptiste van Helmont stated that scorpions could be manufactured by carving an indentation in to a brick, filling the hole with basil and covering the arrangement with another brick.

After leaving it in the sun for a couple of days, one could return to the brick formation and would be amazed to find that

“fumes from the basil, acting as a leavening agent, will have transformed the vegetable matter into veritable scorpions”!

Other Examples

  • Wet soil after a flood was believed to create amphibians such as frogs and toads.
  • Garbage in the streets was thought to create rats.
  • Salamanders were thought to be borne within fire (they often hide inside logs and were probably trying to escape the blaze!).
  • Oyster shells were believed to form as the earth solidified around them and the “vital heat” grew the creature within.
  • Crocodiles in Egypt were thought to have emerged from the mud with the sunshine as a catalyst.

The Disproving of Spontaneous Generation Theory

Francesco Redi, 1626-1697

Francesco Redi was an Italian physician and the first scientist to suspect that the theory of spontaneous generation may be flawed, so he set up a simple experiment. He placed fresh meat into two different jars, one with a muslin cloth over the top, and the other left open. A few days later, the open jar contained maggots, while the covered container did not. He saw this as proof that maggots had to come from fly eggs and could not spontaneously generate.

John Needham, 1731-1781

Over 100 years later, John Needham, an English naturalist and an avid supporter of spontaneous generation theory, performed an experiment in which he boiled up a broth and poured it into a covered flask—at this time, people were aware that the process of boiling removed the microorganisms that they called “animacules”. After a short while, the broth was filled with microorganisms, a revelation to Needham who claimed these had arisen through spontaneous generation. His experiment was contested for the fact he did not heat the broth for long enough and his animacules were heat resistant.

Lazzaro Spallanzani, 1729-1799

Another Italian scientist, Lazzaro Spallanzani, performed a similar experiment to Needham and found that if the broth was heated after the flask was sealed rather than before, the organisms did not generate. He decided that Needham’s broths had been contaminated between the boiling pan and the flask.

Needham’s response claimed that air was necessary for spontaneous generation and that the “vital heat” in the air had been destroyed during Spallanzani’s experiment.

Louis Pasteur, 1822 – 1895

Finally in 1859, a French scientist named Louis Pasteur designed a series of flasks with the necks bent into an S shape. The necks were fashioned so that fresh air could reach the flasks, but were bent in such a way that any air-borne microbes would be trapped at the bottom of the curves.

He boiled the broth inside the flask and did not see any microbes in the broth for many months. When he eventually removed the top from the flask and left it off, he found the liquid to be teaming with microorganisms within a few days. Therefore, he had proved that the microbes from which life arises are present within the air and are not spontaneously generated!

Experiment Pasteur
The image shows a simple diagram of Pasteur’s experiment.


1. What was wrong with John Needham’s experiment?
A. He contaminated his sample
B. His sample was too small
C. He did not leave his sample for enough time
D. He did not use the right type of broth

Answer to Question #1
A is correct. John Needham’s samples were contaminated between boiling and being poured in to the flask. Lazzaro Spallanzani was able to show this by boiling the sample in the flask.

2. Why did Louis Pasteur make an S shape neck for his flasks?
A. So that the air could escape
B. So that the microbes would be collected
C. To help the microbes reach the fluid
D. So it was easier to hold

Answer to Question #2
B is correct. The S shape tube, which faced down prevented microbes entering the liquid as they were collected by gravity along the bends.


  • Boundless. “Pasteur and Spontaneous Generation.” Boundless Microbiology Boundless. Retrieved from www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/introduction-to-microbiology-1/introduction-to-microbiology-18/pasteur-and-spontaneous-generation-205-5188/
  • Laura Moss (2014) How to make a mouse: The bizarre ‘recipes’ borne of spontaneous generation. Mother Nature Network. Retrieved from: http://www.mnn.com/green-tech/research-innovations/stories/how-to-make-a-mouse-the-bizarre-recipes-borne-of-spontaneous
  • Matt Simon (2014) Fantastically Wrong: Why people once thought that mice grew out of wheat and sweaty shirts. WIRED. Retrieved from:https://www.wired.com/2014/06/fantastically-wrong-how-to-grow-a-mouse-out-of-wheat-and-sweaty-shirts/
  • Phillip Ball (2016) Man Made: A History of Synthetic Life. Distillations. Chemical Heritage Foundation. Retrieved from:https://www.chemheritage.org/distillations/magazine/man-made-a-history-of-synthetic-life
  • Origin of Life: Spontaneous Generation (2017) Infoplease. Retrieved From: https://www.infoplease.com/science/biology/origin-life-spontaneous-generation
  • Mark Kusinitz. (2017) Spontaneous Generation. JRank. Retrieved from: http://science.jrank.org/pages/6408/Spontaneous-Generation.html