Spontaneous generation was the idea that living things could be produced by non-living things.
Those who promoted this idea based it on observations, but they did not experiment to test their ideas.
Following are examples of observations leading to the idea of spontaneous generation.
1. Observation: Farmers found mice in moldy grain.
Conclusion: Moldy grain produces mice.
Observation: Before refrigeration, butchers hung meat and sliced off pieces for customers. In the summer, flies swarmed around the hanging meat.
Conclusion: Warm hanging meat produced flies.
In 1668, Francesco Redi, an Italian physician, was convinced that life could only come from life. He was even more specific, flies could only come from flies just like humans come from other humans.
Redi carried the observations further and experimented.
Observation: There are flies around meat carcasses at the butcher shop.
Question: What affect does rotting meat have on the production of flies?
Hypothesis: Rotten meat does not turn into flies. Only flies can make more flies.
Prediction: If meat cannot turn into flies, rotting meat in a sealed (fly-proof) container should not produce flies or maggots.
1. The jars and the meat used for each experimental jar are as identical as possible.
2. Three groups of jars are prepared. The more jars used in each group the more reliable will be the results.
control group — These jars of meat have no lid.
experimental group 1 — The jars in this group are sealed with lids.
experimental group 2- The jars in this group have their mouths covered with a single layer of cheese cloth (a gauze pad works).
3. Observe the contents of the jars one or more times each day. Make note of the presence or absence of flies and maggots in each jar.
Data: Photos of the jars during the investigation can be used to record data.
Control Group: Flies were seen entering the jars. Maggots appeared within one day and at the end of 7 days there were maggots and flies in the jar.
Experimental Group 1: These closed jars had no maggots or flies.
Experimental Group 2: In these gauze-covered jars, no flies were seen entering the jars. Like all the jars, flies were seen around the jars and for this group they were observed on the gauze covering. Later maggots were seen on the gauze covering and on the meat inside the jar. After maggots were seen inside the jars the pupae stage of the fly were seen and then flies. meat.
Conclusion: So What Happened?
Only flies can make more flies.
Control Group: In the uncovered jars of this group, flies entered and laid eggs on the meat. Maggots hatched from these eggs and formed pupae from which flies emerged.
Experimental Group 1: In these sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars.
Experimental Group 2: Adult flies laid eggs on the gauze covering the openings of these jars. These eggs or the maggots from them fell through the opening in the gauze. The eggs and maggots inside these jars developed in the same way as those in the control jars.m
Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for flies.
FYI: Redi’s experiment did not end the idea of spontaneous generation, instead it was altered some. The new idea was that only very small living things were produced by spontaneous generation.
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