Spontaneous Generation Theory

The spontaneous generation theory is one of those theories that was once used to define the origin of life. According to this theory, life could have arisen from non-living matter, provided that the environmental conditions suited the existence of living organisms. Aristotle first put forth this theory, and people sternly believed it until the 17th century.

In this article, we will read about what spontaneous generation theory is, Aristotle and his relation to spontaneous generation theory, scientific investigations that were carried out, why spontaneous generation theory got disapproved, and misconceptions related to spontaneous generation theory.

What is Spontaneous Generation Theory?

The spontaneous generation theory is one of those theories that explains the origin of life. According to this theory, life could originate from non-living matter like decaying meat or other organic substances. Aristotle proposed this theory, and it remained one of the most widely accepted theories until the 17th century. After the scientific advancement took place, opportunities came, and many experiments were conducted that concluded against the theory and led to its disproval in the 19th century.

Aristotle and the Classical View

The ancient Greek philosopher Aristotle held beliefs that aligned with the idea of spontaneous generation. In his work “History of Animals” and other writings, Aristotle proposed that certain living organisms could arise spontaneously from non-living matter. He believed that life could originate from the interaction of the elements like soil, water, air, and fire. Aristotle did not have access to modern experimental setups hence his views were rooted in observations of the natural world, suggesting that insects and small creatures could originate from the transformation of substances such as mud or decaying matter.

Scientific Investigations and Debunking

The theory of spontaneous Generation was believed sternly till 17th Century. However, during the renaissance several scientific advancement took place that made it possible for the scientists to conduct experiments in support or against the concept of this theory. Some of these experiments on Spontaneous generation are discussed further.

Experiments of Pier Antonio Micheli (1679–1737)

Pier Antonio Micheli was an Italian botanist and mycologist. He is best known for his pioneering work in the field of mycology and for his observations on fungi and plant diseases. His works did not directly refute the spontaneous generation theory but his experiments in which he showed that fungal spores led to the growth of fungus on bread somewhere challenged the theory that stated life could originate without the existence of pre-existing life forms.

Experiments of John Needham (1713–1781)

John Needham was a naturalist and biologist who conducted experiments related to the theory of spontaneous generation in the mid-18th century. In a series of experiments, Needham investigated the idea that living organisms could arise spontaneously from non-living matter. He conducted experiments with infusions, which involved boiling various nutrient broths and then sealing them in containers.

Despite the heat treatment, Needham observed the appearance of microorganisms in the sealed containers. Needham interpreted these observations as evidence supporting spontaneous generation, suggesting that life could emerge from the boiled infusions. However, his experiments faced criticism, particularly from fellow naturalist and microbiologist Lazzaro Spallanzani.

Experiments of Lazzaro Spallanzani (1729–1799)

Lazzaro Spallanzani conducted his own experiments to challenge Needham’s findings. He argued that Needham’s sealing of the containers was not entirely effective, allowing external contaminants to enter and introduce microorganisms.

To prove this, he repeated Needham’s experiment but sealed the broth containers more securely and observed that, under proper conditions, no microbial growth occurred. He argued that the absence of growth was due to the exclusion of external contaminants rather than the absence of a vital force necessary for spontaneous generation.

Disapproval of Spontaneous Generation Theory

Although several experiments were conducted that challenged the theory of spontaneous generation, the theory was finally disapproved in the 19th Century post the experiments of Louis Pasteur that were also supported by the evidences put forward by John Tyndall.

Experiments of Francesco Redi (1626–1697)

Francesco Redi was an Italian physician and naturalist who conducted a series of experiments in the 1660s that challenged the idea of spontaneous generation of organisms like mice, insects, etc. on dead and decaying matter. In one of his most famous experiments, Redi placed meat in three different jars: one uncovered, one covered with gauze, and one completely sealed.

The jar with no coverings allowed flies to lay their eggs on the meat, leading to the development of maggots. The jar covered with gauze prevented adult flies from landing directly on the meat, and as a result, no maggots appeared on meat. The sealed jar, which was completely isolated from external factors, also showed no signs of maggot formation. Redi’s experiments demonstrated that living organisms like maggots, did not spontaneously generate from the meat but rather came from the eggs laid by flies.

Experiments of Louis Pasteur (1822–1895)

In the 19th century, Louis Pasteur conducted experiments that decisively denied the theory of spontaneous generation. In his series of experiments, he placed sterile nutrient broths in swan neck flasks. Following are its important points.

• The flasks were designed in such a way that their curved necks allowed only air to enter but prevented dust and microorganisms from reaching the broth. Under this condition, the broth remained clear for long time supporting the fact that no microbial growth occurred in these flasks.
• When these flasks were turned to allow the contaminants to enter, the broth turned cloudy after few hours. This proved that the growth of microbes in the flask occured when microbes entered the flask from outside and not spontaneously.

Experiments of John Tyndall (1820–1893)

John Tyndall was and Irish physicist whose experiments were particularly focused on demonstrating the presence of microorganisms in the air and their role in contaminating sterile solutions. He designed experiments to show that, even when seemingly pure air was used, microorganisms could still be introduced and lead to the development of life in a nutrient-rich environment. Following are its important points:

• In one of his notable experiments, Tyndall devised a setup involving a sealed tube with a nutrient broth. He exposed the nutrient broth to air that had been filtered through cotton, effectively removing solid particles.
• Tyndall found that, under these conditions, no microbial growth occurred. This demonstrated that the absence of particulate matter in the air prevented the introduction of microorganisms into the nutrient broth.
• Tyndall also experimented with heat to sterilize air. He used a device known as the “Tyndall box,” which had a tube containing a heated copper coil.
• As air passed through the coil, it was effectively sterilized by the heat. And when this air was introduced into the nutrient media, no microbial growth occurred.

Misconceptions and Popular Culture

The spontaneous generation theory was backed by various general observations, and since no proper scientific methods were available in those times, it was not possible to provide experimental proofs to support the origin of life. There were some popular beliefs and observations that led to the popularity of this theory. Some of them are discussed below.

• The Idea of Magical Mud: In ancient times, the occurrence of frogs and insects near some muddy water bodies made people believe that the pools contained magical mud, and in the presence of moisture, the non-living matter of the magical mud combined to give rise to living organisms.
• Spontaneous appearance of maggots on rotting meat: It was observed that if a piece of meat was left open, in a few hours, maggots appeared on it. This was believed to be spontaneous generation because no experiments were conducted then to prove the laying of eggs by the flies that visited the meat.
• Concept of vital heat that could lead to the generation of life: When a container with decaying organic material was heated and then sealed, colonies of microorganisms grew inside it. This observation made people believe that the heating process created suitable conditions that led to the spontaneous generation of life.
• Natural forces triggering the generation of life: Early civilizations considered air, water, soil, fire, and sunlight to be supreme forces of nature, and they together forced the origin of life on Earth without any precursor.
• Recipe for Making Mice: According to this belief, worn underwear, if left in an open jar containing wheat husk for 21 days, will give rise to mice.
• Recipe for producing scorpions: Jean-Baptiste van Helmont, a European chemist, believed that he could manufacture scorpions by filling crevices of bricks with basil and leaving them under sunlight for a couple of days.

There were many more beliefs, like garbage acting as a precursor for rats, fire being the progenitor of salamanders, vital heat leading to the generation of organisms inside oyster shells that were thought to be solidified earth, the emergence of crocodiles from mud catalysed by sunlight, etc.

Conclusion: Sponataneous Generation Theory

Pasteur’s experiments conclusively established the principle of biogenesis, stating that living organisms only arise from pre-existing living organisms. His work not only disproved the spontaneous generation theory but also solidified the recognition of the biogenic origin of life by the scientific community. At last in 1862, the French Academy of Sciences decided to award the scientists who were involved in this debate and put forth effective conclusions to identify the origin of life. Louis Pasteur received Alhumbert Prize for his works and since then the concept of biogenesis replaced the long existing theory of sponatneous generation.

FAQs – Spontaneous Generation Theory

Who is the Father of Spontaneous Generation Theory?

Aristotle is the father of spontaneous generation theory. He was the first person to put forward substantial observation in support of the spontaneous generation theory.

What is the Main argument of the Spontaneous Generation Theory?

The main argument of spontaneous generation theory was that life could generate from non-living or decaying organic matter.

Who Disproved the Theory of Spontaneous Generation ?

Louis Pasteur, a French microbiologist, is credited for disproving the theory of spontaneous generation in the mid-19th century.

Can Life Spontaneously Generate?

No, life cannot generate spontaneously. The concept of spontaneous generation has been debunked by scientific understanding, and living organisms arise from pre-existing living organisms through the process of biogenesis.

What is the Difference between Spontaneous Generation and Biogenesis?

Spontaneous generation means that living organisms could arise spontaneously from non-living matter whereas biogenesis means that new living organisms can arise from pre-existing living organisms only.