Controversy over Spontaneous Generation, Francesco Redi, Origin of Life, Simple Experiments, Abiogenesis

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Home >> Microbiology >>Controversy over Spontaneous Generation

	Controversy over Spontaneous Generation Actually, it was the discovery of microorganisms and improvements in microscopy that enabled scientists to think seriously about the origin of life. Francesco Redi (1626-1679), an Italian physician, demonstrated during mid 17th century by simple experiments that spontaneous generation (abiogenesis) does not exist. He took rotting meat pieces and placed them in jars. He sealed some of these jars tightly and left others open. In a few days, maggots appeared in open jars in which the flies went freely in and out and laid their eggs on meat. Contrary to it, the sealed jars in which the flies could not enter did not show any maggots.
From these observations Redi concluded that the maggots arise from the eggs laid down by the parent flies and that the maggots can not appear spontaneously. Still, the supporters of abiogenesis did not agree with Redi and argued that the free air, which was considered as "vital force" necessary for spontaneous origin of life, was not allowed to reach the meat placed in sealed jars. So Redi set up new set of experiment in which he covered jars with fine muslin cloth or gauze instead of sealing them tightly and thus allowed free air to go in and out of the jars. Even after doing so the maggots appeared only in those jars in which flies were allowed free to go in and lay their eggs on the meat.
Even after Redi's convincing demonstration, abiogenesis versus biogenesis controversy continued. John Needham (1745) advocated that even after he heated chicken broth and corn infusions (nutrient fluids) before pouring them into covered flasks, the cooled solutions showed existence of tiny organisms in them and thus he claimed that the organisms originated spontaneously from the nutrient fluids. We shall see later that this result was due to insufficient heating which failed to kill heat resistant forms of bacteria containing endospores. But nothing was known about endospores at that time.
In the year 1765, twenty years later Lazzaro Spallanzani demonstrated that nutrient fluids of Needham did not contain microorganisms when they were subjected to prolong heating after being sealed in flasks. He explained that the microorganisms from air probably had entered Needham's solutions after they were boiled. Needham responded to it and said that the free air, the "vital force", present inside Spallanzani's sealed flasks had been destroyed by heating and, therefore, microorganisms did not appear in nutrient fluids in absence of the "vital force".

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