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Theory of spontaneous generation by Aristotle 350 B.C

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Theory of spontaneous generation by Aristotle 350 B.C

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The Greek philosopher Aristotle (384–322 BC) was one of the earliest recorded scholars to articulate the theory of

Aristotle wrote about the formation of insects from the dew that fell on the leaves or from the hair, meat or animal parts

This theory persisted into the 17th century, when scientists undertook additional experimentation to support or disprove it.

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Theophrastus theory of spontaneous generation

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Theophrastus theory of spontaneous generation

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Spontaneous generation is the formation of living organisms from non-living matter. The Greek philosopher and botanist named Theophrastus claimed that a plant called silphium had emerged from the earth where it was not present before and described this phenomenon as an example of spontaneous generation.

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Theory of spontaneous generation by Paracelsus

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Theory of spontaneous generation by Paracelsus

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In the 16th century, the Swiss German botanist and astrologer Paracelsus cited observations of the spontaneous generation of mice, frogs, and eels from water, air, or decaying matter.

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In the 17th century, some biologists thought that the simplest forms of life were generated by spontaneus generation from inactive/ dead matter. This was rejected with experiments when, mice were born from mother mice after they copulated with father mice. But, there were still many doubts about these theories, for example, insects whose reproductive cycle was unknown.

To test the hypothesis, Francesco Redi placed fresh meat in open containers [left, above]. As expected, the rotting meat attracted flies, and the meat was soon swarming with maggots, which hatched into flies [left, below]. When the jars were tightly covered so that flies could not get in [middle, above], no maggots were produced [middle, below]. To answer the objection that the cover cut off fresh air necessary for spontaneous generation, Redi covered the jars with several layers of porous gauze [right, above] instead of an air-tight cover. Flies were attracted to the smell of the rotting meat, clustered on the gauze, which was soon swarming with maggots, but the meat itself remained free of maggots [right, below]. Thus flies are necessary to produce flies: they do not arise spontaneously from rotting meat.

What Francesco Redi did to test the hypothesis, was to replace fresh meat in open containers, making the flies attracted to the rooting meat. Then the meat was soon swarming with maggots, which hatched into flies. When the jars were tightly covered, making the flies not able to get in the middle, no maggots were produced. Finally, to answer the objection that the cover cut off fresh air necessary for spontaneous generation, Redi covered the jars with several layers of porous gauze instead of an air-tight cover. Flies were attracted to the smell of the rotting meat, clustered on the gauze, which was soon swarming with maggots, but the meat itself remained free of maggots. So, flies are necessary to produce flies: they do not arise spontaneously from rotting meat.

Redi went on to demonstrate that dead maggots or flies would not generate new flies when placed on rotting meat in a sealed jar, whereas live maggots or flies would. This disproved both the existence of some essential component in once-living organisms, and the necessity of fresh air to generate life.

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Lazzaro Spallanzani experiment (1765 - 1767)

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Lazzaro Spallanzani experiment (1765 - 1767)

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A few years later (1765 - 1767), Lazzaro Spallanzani, an Italian abbot and biologist, tried several variations on Needham's soup experiments. First, he boiled soup for one hour, then sealed the glass flasks that contained it by melting the mouths of the flasks shut.( Soup in those flasks stayed sterile). He then boiled another batch of soup for only a few minutes before sealing the flasks, and found that microorganisms grew in that soup. In a third batch, soup was boiled for an hour, but the flasks were sealed with real-cork corks (which, thus, were loose-fitting enough to let some air in), and microorganisms grew in that soup. Spallanzani concluded that while one hour of boiling would sterilize the soup, only a few minutes of boiling was not enough to kill any bacteria initially present, and the microorganisms in the flasks of spoiled soup had entered from the air.

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Louis Pasteur’s 1859 experiment is widely seen as having settled the question. His experiment consisted in:
1) boilng a meat broth in a flask that had a long neck that curved downward
2) When the flask was turned so that particles could fall down the bends, the broth quickly became clouded.
3)  Pasteur exposed boiled broths to air in vessels that contained a filter to prevent all particles from passing through to the growth medium, and even in vessels with no filter at all, with air being admitted via a long tortuous tube that would not allow dust particles to pass.
4) Nothing grew in the broths unless the flasks were broken open, showing that the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously generated within the broth.

This was one of the last and most important experiments disproving the theory of spontaneous generation.

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Origin of the first cell from non-living matter. Include at least four hypotheses for each step of the process (Includes experiment by S. Miller and H. Urey)

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Origin of the first cell from non-living matter. Include at least four hypotheses for each step of the process (Includes experiment by S. Miller and H. Urey)

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The Miller-Urey experiment provided the first evidence that organic molecules needed for life could be formed from inorganic components.The cell theory, which has been around since the 1880s, holds that cells can only form through the division of a previous cell. This hypothesis has been supported by solid evidence.

The implication of this hypothesis is remarkable, as every cell in our body was formed through the division of a previous cell, with the complete copy of the genetic material from the nucleus for each cell. The origin of the cells of our body goes back to the zygote, which is the first cell that begins our life when a sperm and an egg fuse. Sperm and eggs, in turn, were produced by cell division in our parents.The first artificial cell, created in 2010, was synthesized from the base sequence of the DNA of an existing bacterium, with some intentional changes, and transferred to cells of a different and previously existing type of bacteria.
Talking about hypothesis, the first hypothesis regarding the origin of life is Abiogenesis. This hypothesis suggests that life originated from non-living matter through natural processes without the need for a supernatural creator. The Miller-Urey experiment demonstrated in 1952 showed how complex organic molecules, such as amino acids, could be synthesized from simple inorganic compounds, including methane, ammonia, water, and hydrogen, under conditions that mimicked the early Earth's atmosphere. Through other similar experiments using different starting materials under varied conditions, various biomolecules were synthesized, including sugars and lipids.

The next hypothesis is Panspermia, which suggests that life on Earth originated from microorganisms that arrived here from other planets or moons. These microorganisms were ejected from their home world by asteroid impact or other cosmic events, and life did not arise on Earth itself, but rather was transported here.

The RNA world hypothesis proposes that RNA was the first information-carrying molecule and played a crucial role in the origin of life. According to this hypothesis, RNA molecules with catalytic properties could have emerged spontaneously from prebiotic conditions and acted as the first enzymes, replicating themselves and evolving into more complex structures.

Chemoautotrophy hypothesis suggests that life originated in deep-sea hydrothermal vents, where mineral-rich water and gases spewed from Earth's interior. In this scenario, primitive bacteria used energy from chemical reactions, rather than sunlight, to generate metabolic energy and build complex organic molecules.

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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 place of origin of the first

Carbon compounds are the vents in the

ocean floor. These vents are cracks in

the superficies of the Earth and they are characterized by

hot water with chemical compounds

and reduced inorganics, for example the sulfide.

These chemical compounds represent a

accessible power source for the assembly of

These carbon compounds in polymers

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Endosymbiotic theory including evidence that sustains it.

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Endosymbiotic theory including evidence that sustains it.

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The endosymbiosis theory is useful in explaining the evolution of eukaryotic cells, in this case of the origin of mitochondria and chloroplasts. According to this theory, mitochondria were once independent prokaryotic organisms that had developed the process of aerobic cellular respiration. Larger prokaryotes that could only carry out anaerobic respiration absorbed the smaller aerobic prokaryotes through endocytosis, but instead of digesting them, it allowed them to survive in their cytoplasm. The smaller prokaryotes could exist indefinitely within the larger cells as long as they grew and divided at the same rate. This symbiotic relationship was mutualistic, as both organisms benefited: the smaller prokaryotes were fed by the larger cell, while they in turn carried out efficient aerobic respiration to supply energy to the larger cell. This relationship was selected for by natural selection, leading to the development of the mitochondria in current eukaryotic cells.

The endosymbiosis theory also explains the origin of chloroplasts. If a prokaryote that had developed photosynthesis had been absorbed by a larger cell that allowed it to survive, grow and divide, it could have developed into the chloroplasts of photosynthetic eukaryotes. Again, both organisms would have benefited from this endosymbiotic relationship.

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Biology book-28/04/23
Hypotheses about the origins of life (article) | Khan Academy. (s. f.). Khan Academy. https://www.khanacademy.org/science/ap-biology/natural-selection/origins-of-life-on-earth/a/hypotheses-about-the-origins-of-life

Rogers, K. (2011b, agosto 29). Abiogenesis | Definition & Theory. Encyclopedia Britannica. https://www.britannica.com/science/abiogenesis

J, P. P., & Merino, M. (2022). Panspermia - Qué es, definición y concepto. Definición.de. https://definicion.de/panspermia/#:~:text=La%20panspermia%20es%20una%20teor%C3%ADa%20que%20afirma%20que,que%20podr%C3%ADa%20proceder%20de%20otros%20sectores%20del%20universo.

Ácido ribonucleico (ARN). (s. f.). Genome.gov. https://www.genome.gov/es/genetics-glossary/ARN

Button, E. S., Pett-Ridge, J., Murphy, D., Kuzyakov, Y., Chadwick, D. R., & Jones, D. R. (2022). Deep-C storage: Biological, chemical and physical strategies to enhance carbon stocks in agricultural subsoils. Soil Biology & Biochemistry, 170, 108697. https://doi.org/10.1016/j.soilbio.2022.108697