Presentation on theme: "The idea that non-living objects could give rise to living things."— Presentation transcript:
The idea that non-living objects could give rise to living things.
* For centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas to determine the validity of them. * In other words, they did not use the scientific method. Their conclusions were just based on untested observations.
* For centuries it was common knowledge that simple organisms like worms, beetles, frogs, flies and salamanders could come from dust, mud, food, garbage, etc.
* Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving mud that enabled the people to grow that year’s crop of food. However, along with the mud, large numbers of frogs appeared that weren’t around in drier times. * It was obvious to the people that muddy soil gave rise to the frogs.
* In many parts of Europe, medieval farmers stored grain in barns with thatched rooves. As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course mice. * It was obvious to them that the mice came from the moldy grain.
* In early cities, there were no sewers and no garbage trucks. Garbage and the contents of chamber pots were tossed out the nearest window. Rats were rampant on the city streets and not as common in the country. * It was obvious to the people that rats were a product of garbage.
* Since there were no refrigerators, the daily trip to the butcher shop meant battling the flies around the carcasses. * 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. The picture represents the three jars and the variables he used. * Conclusion: In the uncovered jars, flies entered and laid eggs on meat. Maggots hatched and turned into adult flies. No flies could get into the sealed jars, and hence, no maggots hatched. In the gauze covered jars, flies and maggots appeared on the * aapp gauze.
* After this experiment, people were willing to acknowledge that organisms visible to the naked eye didn’t arise by spontaneous generation but had to have parents. * With the development and refinement of the microscope in the 1600s, people began seeing all sorts of new life forms such as yeast, other fungi, bacteria and various protists. Then then believed just these tiny organisms came by spontaneous generation.
* In the 1700s John Needham, a Scottish naturalist, and Spallanzani, an Italian biologist, tested soups and the growth of microorganisms. Needham claimed there was a “life force” present in the molecules in non-living matter like air and oxygen that could cause spontaneous generation to occur because he had bacteria in his soup. * Spallanzani found that one hour of boiling could sterilize the soup so that no microorganisms grew. He felt that the microorganisms were already in the broth and not from the air. * Needham was concerned that Spallanzani had destroyed the life force with his extensive boiling. * They argued over who was right.
* Louis Pasteur tested the notion about life force and sterilization to settle the debate. * He proved that only when bacteria are able to get into the soup did it result in the growth of bacteria. * Hence, bacteria also have to have a parent.
* Reproduction is now one of the characteristics of all living things.