Origin of Life. Aristotle (384 –322 BC). Proposed the theory of spontaneous generation Idea that living things can arise from nonliving matter Idea lasted almost 2000 years. Spontaneous Generation.
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Origin of Life
Proposed the theory of spontaneous generation
Observation:Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times
Conclusion:It was perfectly obvious to people back then that muddy soil gave rise to the frogs
Observation:In many parts of Europe, medieval farmers stored grain in barns with thatched roofs. As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around.
Conclusion:It was obvious to them that the mice came from the moldy grain.
Observation:In the cities centuries ago, there were no sewers, no garbage trucks, no electricity, and no refrigeration. Sewage flowed down the streets. Chamber pots and left-over food were thrown out into the streets each morning. Many cities also had major rat problems and a disease called Bubonic plague.
Conclusion:Obviously, all the sewage and garbage turned into the rats.
Observation:Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses (dead animals). Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them.
Conclusion:Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies.
In 1668, Francesco Redi, an Italian physician, did an experiment with flies and wide-mouth jars containing meat
Evidence against spontaneous generation:1. Unsealed – maggots on meat2. Sealed – no maggots on meat3. Gauze – few maggots on gauze, none on meat
The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way.
If rotting meat is exposed to flies, then flies will lay eggs in rotting meat, because baby maggots will need the rotting meat for food.
Only flies can make more flies. In the uncovered jars, flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggots from them dropped through the gauze onto the meat. In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms.
1668: Francisco Redi
1745: John Needham
1861: Louis Pasteur