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Aristotle around 350 B.C.

According to that theory, pieces of cheese and bread wrapped in rags and left in a dark corner, for example, were thus thought to produce mice, because after several weeks there were mice in the rags. Many believed in spontaneous generation because it explained such occurrences as the appearance of maggots on decaying meat.

By the 18th century it had become obvious that higher organisms could not be produced by nonliving material. The origin of microorganisms such as bacteria, however, was not fully determined until Louis Pasteur proved in the 19th century that microorganisms reproduce.

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Italian physician Francesco Redi (1626–1697), performed an experiment in 1668 that was one of the first to refute the idea that maggots (the larvae of flies) spontaneously generate on meat left out in the open air. He predicted that preventing flies from having direct contact with the meat would also prevent the appearance of maggots. Redi left meat in each of six containers. Two were open to the air, two were covered with gauze, and two were tightly sealed. His hypothesis was supported when maggots developed in the uncovered jars, but no maggots appeared in either the gauze-covered or the tightly sealed jars. He concluded that maggots could only form when flies were allowed to lay eggs in the meat, and that the maggots were the offspring of flies, not the product of spontaneous generation.

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In 1745, John Needham (1713–1781) published a report of his own experiments, in which he briefly boiled broth infused with plant or animal matter, hoping to kill all preexisting microbes. He then sealed the flasks. After a few days, Needham observed that the broth had become cloudy and a single drop contained numerous microscopic creatures. He argued that the new microbes must have arisen spontaneously. In reality, however, he likely did not boil the broth enough to kill all preexisting microbes.

Lazzaro Spallanzani (1729–1799) did not agree with Needham’s conclusions, however, and performed hundreds of carefully executed experiments using heated broth. As in Needham’s experiment, broth in sealed jars and unsealed jars was infused with plant and animal matter. Spallanzani’s results contradicted the findings of Needham: Heated but sealed flasks remained clear, without any signs of spontaneous growth, unless the flasks were subsequently opened to the air. This suggested that microbes were introduced into these flasks from the air. In response to Spallanzani’s findings, Needham argued that life originates from a “life force” that was destroyed during Spallanzani’s extended boiling. Any subsequent sealing of the flasks then prevented new life force from entering and causing spontaneous generation

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The debate over spontaneous generation continued well into the 19th century, with scientists serving as proponents of both sides. To settle the debate, the Paris Academy of Sciences offered a prize for resolution of the problem. Louis Pasteur, a prominent French chemist who had been studying microbial fermentation and the causes of wine spoilage, accepted the challenge. In 1858, Pasteur filtered air through a gun-cotton filter and, upon microscopic examination of the cotton, found it full of microorganisms, suggesting that the exposure of a broth to air was not introducing a “life force” to the broth but rather airborne microorganisms.

Later, Pasteur made a series of flasks with long, twisted necks (“swan-neck” flasks), in which he boiled broth to sterilize it. His design allowed air inside the flasks to be exchanged with air from the outside, but prevented the introduction of any airborne microorganisms, which would get caught in the twists and bends of the flasks’ necks. If a life force besides the airborne microorganisms were responsible for microbial growth within the sterilized flasks, it would have access to the broth, whereas the microorganisms would not. He correctly predicted that sterilized broth in his swan-neck flasks would remain sterile as long as the swan necks remained intact. However, should the necks be broken, microorganisms would be introduced, contaminating the flasks and allowing microbial growth within the broth.

Pasteur’s set of experiments irrefutably disproved the theory of spontaneous generation and earned him the prestigious Alhumbert Prize from the Paris Academy of Sciences in 1862. In a subsequent lecture in 1864, Pasteur articulated “Omne vivum ex vivo” (“Life only comes from life”). In this lecture, Pasteur recounted his famous swan-neck flask experiment, stating that “…life is a germ and a germ is life. Never will the doctrine of spontaneous generation recover from the mortal blow of this simple experiment.” To Pasteur’s credit, it never has

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Origin of the first cell from non-living matter

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Origin of the first cell from non-living matter

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Scientists passed vapor through a mix of     Methane (CH4), Hydrogen (H2), and Ammonia (NH3), to represent atmospheric gases from the beginning of the earth.  They used electric discharges as a source of energy. Amino acids were formed and other carbon compounds necessary for life. Amino acids are the basic units of proteins.

The Oparin-Haldane hypothesis suggests that life arose gradually from inorganic molecules, with “building blocks” like amino acids forming first and then combining to make complex polymers.
The Miller-Urey experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components.
Some scientists support the RNA world hypothesis, which suggests that the first life was self-replicating RNA. Others favor the metabolism-first hypothesis, placing metabolic networks before DNA or RNA.

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In 1953, Stanley Miller and Harold Urey did an experiment to test Oparin and Haldane’s ideas. They found that organic molecules could be spontaneously produced under reducing conditions thought to resemble those of early Earth.

Miller and Urey built a closed system containing a heated pool of water and a mixture of gases that were thought to be abundant in the atmosphere of early earth.To simulate the lightning that might have provided energy for chemical reactions in Earth’s early atmosphere, Miller and Urey sent sparks of electricity through their experimental system.

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Assembly of carbon compounds into polymers.

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Assembly of carbon compounds into polymers.

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A possible site for the origin of the first carbon compounds is around deep-sea vents. These are cracks in the Earth's surface, characterized by gushing hot water carrying reduced inorganic chemicals such as iron sulphide. These chemicals represent readily accessible supplies of energy.

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The mitochondrion  was a free prokaryote that developed the respiration process.
The mitochondrion where “eaten” by prokaryotes thru the process of endocytosis and instead of digesting them, they live inside their hostage cytoplasm.
The mitochondrion and the prokaryote organism had a symbiotic relationship helped by each other (mutualism).
The natural selection favored this kind of cells.
This theory also explains the formation of chloroplasts.

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Allot, A & Mindorff, D. (2014). Biology Course Companion. United Kingdom: Oxford University press.

Editions SM.SM .(2012) .

Spontaneous generation | Examples & Experiments | Britannica. (2023). In Encyclopædia Britannica. https://www.britannica.com/science/spontaneous-generation

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Keenleyside, W. (2019, July 23). 3.1 Spontaneous Generation. Pressbooks.pub; Pressbooks. https://ecampusontario.pressbooks.pub/microbio/chapter/spontaneous-generation/

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Khan Academy. (2023). Khanacademy.org. https://www.khanacademy.org/science/ap-biology/natural-selection/origins-of-life-on-earth/a/hypotheses-about-the-origins-of-life

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