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.

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.